1config ARCH 2 string 3 option env="ARCH" 4 5config KERNELVERSION 6 string 7 option env="KERNELVERSION" 8 9config DEFCONFIG_LIST 10 string 11 depends on !UML 12 option defconfig_list 13 default "/lib/modules/$UNAME_RELEASE/.config" 14 default "/etc/kernel-config" 15 default "/boot/config-$UNAME_RELEASE" 16 default "$ARCH_DEFCONFIG" 17 default "arch/$ARCH/defconfig" 18 19config CONSTRUCTORS 20 bool 21 depends on !UML 22 23config IRQ_WORK 24 bool 25 26config BUILDTIME_EXTABLE_SORT 27 bool 28 29config THREAD_INFO_IN_TASK 30 bool 31 help 32 Select this to move thread_info off the stack into task_struct. To 33 make this work, an arch will need to remove all thread_info fields 34 except flags and fix any runtime bugs. 35 36 One subtle change that will be needed is to use try_get_task_stack() 37 and put_task_stack() in save_thread_stack_tsk() and get_wchan(). 38 39menu "General setup" 40 41config BROKEN 42 bool 43 44config BROKEN_ON_SMP 45 bool 46 depends on BROKEN || !SMP 47 default y 48 49config INIT_ENV_ARG_LIMIT 50 int 51 default 32 if !UML 52 default 128 if UML 53 help 54 Maximum of each of the number of arguments and environment 55 variables passed to init from the kernel command line. 56 57 58config CROSS_COMPILE 59 string "Cross-compiler tool prefix" 60 help 61 Same as running 'make CROSS_COMPILE=prefix-' but stored for 62 default make runs in this kernel build directory. You don't 63 need to set this unless you want the configured kernel build 64 directory to select the cross-compiler automatically. 65 66config COMPILE_TEST 67 bool "Compile also drivers which will not load" 68 depends on !UML 69 default n 70 help 71 Some drivers can be compiled on a different platform than they are 72 intended to be run on. Despite they cannot be loaded there (or even 73 when they load they cannot be used due to missing HW support), 74 developers still, opposing to distributors, might want to build such 75 drivers to compile-test them. 76 77 If you are a developer and want to build everything available, say Y 78 here. If you are a user/distributor, say N here to exclude useless 79 drivers to be distributed. 80 81config LOCALVERSION 82 string "Local version - append to kernel release" 83 help 84 Append an extra string to the end of your kernel version. 85 This will show up when you type uname, for example. 86 The string you set here will be appended after the contents of 87 any files with a filename matching localversion* in your 88 object and source tree, in that order. Your total string can 89 be a maximum of 64 characters. 90 91config LOCALVERSION_AUTO 92 bool "Automatically append version information to the version string" 93 default y 94 depends on !COMPILE_TEST 95 help 96 This will try to automatically determine if the current tree is a 97 release tree by looking for git tags that belong to the current 98 top of tree revision. 99 100 A string of the format -gxxxxxxxx will be added to the localversion 101 if a git-based tree is found. The string generated by this will be 102 appended after any matching localversion* files, and after the value 103 set in CONFIG_LOCALVERSION. 104 105 (The actual string used here is the first eight characters produced 106 by running the command: 107 108 $ git rev-parse --verify HEAD 109 110 which is done within the script "scripts/setlocalversion".) 111 112config HAVE_KERNEL_GZIP 113 bool 114 115config HAVE_KERNEL_BZIP2 116 bool 117 118config HAVE_KERNEL_LZMA 119 bool 120 121config HAVE_KERNEL_XZ 122 bool 123 124config HAVE_KERNEL_LZO 125 bool 126 127config HAVE_KERNEL_LZ4 128 bool 129 130choice 131 prompt "Kernel compression mode" 132 default KERNEL_GZIP 133 depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4 134 help 135 The linux kernel is a kind of self-extracting executable. 136 Several compression algorithms are available, which differ 137 in efficiency, compression and decompression speed. 138 Compression speed is only relevant when building a kernel. 139 Decompression speed is relevant at each boot. 140 141 If you have any problems with bzip2 or lzma compressed 142 kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older 143 version of this functionality (bzip2 only), for 2.4, was 144 supplied by Christian Ludwig) 145 146 High compression options are mostly useful for users, who 147 are low on disk space (embedded systems), but for whom ram 148 size matters less. 149 150 If in doubt, select 'gzip' 151 152config KERNEL_GZIP 153 bool "Gzip" 154 depends on HAVE_KERNEL_GZIP 155 help 156 The old and tried gzip compression. It provides a good balance 157 between compression ratio and decompression speed. 158 159config KERNEL_BZIP2 160 bool "Bzip2" 161 depends on HAVE_KERNEL_BZIP2 162 help 163 Its compression ratio and speed is intermediate. 164 Decompression speed is slowest among the choices. The kernel 165 size is about 10% smaller with bzip2, in comparison to gzip. 166 Bzip2 uses a large amount of memory. For modern kernels you 167 will need at least 8MB RAM or more for booting. 168 169config KERNEL_LZMA 170 bool "LZMA" 171 depends on HAVE_KERNEL_LZMA 172 help 173 This compression algorithm's ratio is best. Decompression speed 174 is between gzip and bzip2. Compression is slowest. 175 The kernel size is about 33% smaller with LZMA in comparison to gzip. 176 177config KERNEL_XZ 178 bool "XZ" 179 depends on HAVE_KERNEL_XZ 180 help 181 XZ uses the LZMA2 algorithm and instruction set specific 182 BCJ filters which can improve compression ratio of executable 183 code. The size of the kernel is about 30% smaller with XZ in 184 comparison to gzip. On architectures for which there is a BCJ 185 filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ 186 will create a few percent smaller kernel than plain LZMA. 187 188 The speed is about the same as with LZMA: The decompression 189 speed of XZ is better than that of bzip2 but worse than gzip 190 and LZO. Compression is slow. 191 192config KERNEL_LZO 193 bool "LZO" 194 depends on HAVE_KERNEL_LZO 195 help 196 Its compression ratio is the poorest among the choices. The kernel 197 size is about 10% bigger than gzip; however its speed 198 (both compression and decompression) is the fastest. 199 200config KERNEL_LZ4 201 bool "LZ4" 202 depends on HAVE_KERNEL_LZ4 203 help 204 LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding. 205 A preliminary version of LZ4 de/compression tool is available at 206 <https://code.google.com/p/lz4/>. 207 208 Its compression ratio is worse than LZO. The size of the kernel 209 is about 8% bigger than LZO. But the decompression speed is 210 faster than LZO. 211 212endchoice 213 214config DEFAULT_HOSTNAME 215 string "Default hostname" 216 default "(none)" 217 help 218 This option determines the default system hostname before userspace 219 calls sethostname(2). The kernel traditionally uses "(none)" here, 220 but you may wish to use a different default here to make a minimal 221 system more usable with less configuration. 222 223config SWAP 224 bool "Support for paging of anonymous memory (swap)" 225 depends on MMU && BLOCK 226 default y 227 help 228 This option allows you to choose whether you want to have support 229 for so called swap devices or swap files in your kernel that are 230 used to provide more virtual memory than the actual RAM present 231 in your computer. If unsure say Y. 232 233config SYSVIPC 234 bool "System V IPC" 235 ---help--- 236 Inter Process Communication is a suite of library functions and 237 system calls which let processes (running programs) synchronize and 238 exchange information. It is generally considered to be a good thing, 239 and some programs won't run unless you say Y here. In particular, if 240 you want to run the DOS emulator dosemu under Linux (read the 241 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>), 242 you'll need to say Y here. 243 244 You can find documentation about IPC with "info ipc" and also in 245 section 6.4 of the Linux Programmer's Guide, available from 246 <http://www.tldp.org/guides.html>. 247 248config SYSVIPC_SYSCTL 249 bool 250 depends on SYSVIPC 251 depends on SYSCTL 252 default y 253 254config POSIX_MQUEUE 255 bool "POSIX Message Queues" 256 depends on NET 257 ---help--- 258 POSIX variant of message queues is a part of IPC. In POSIX message 259 queues every message has a priority which decides about succession 260 of receiving it by a process. If you want to compile and run 261 programs written e.g. for Solaris with use of its POSIX message 262 queues (functions mq_*) say Y here. 263 264 POSIX message queues are visible as a filesystem called 'mqueue' 265 and can be mounted somewhere if you want to do filesystem 266 operations on message queues. 267 268 If unsure, say Y. 269 270config POSIX_MQUEUE_SYSCTL 271 bool 272 depends on POSIX_MQUEUE 273 depends on SYSCTL 274 default y 275 276config CROSS_MEMORY_ATTACH 277 bool "Enable process_vm_readv/writev syscalls" 278 depends on MMU 279 default y 280 help 281 Enabling this option adds the system calls process_vm_readv and 282 process_vm_writev which allow a process with the correct privileges 283 to directly read from or write to another process' address space. 284 See the man page for more details. 285 286config FHANDLE 287 bool "open by fhandle syscalls" if EXPERT 288 select EXPORTFS 289 default y 290 help 291 If you say Y here, a user level program will be able to map 292 file names to handle and then later use the handle for 293 different file system operations. This is useful in implementing 294 userspace file servers, which now track files using handles instead 295 of names. The handle would remain the same even if file names 296 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2) 297 syscalls. 298 299config USELIB 300 bool "uselib syscall" 301 def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION 302 help 303 This option enables the uselib syscall, a system call used in the 304 dynamic linker from libc5 and earlier. glibc does not use this 305 system call. If you intend to run programs built on libc5 or 306 earlier, you may need to enable this syscall. Current systems 307 running glibc can safely disable this. 308 309config AUDIT 310 bool "Auditing support" 311 depends on NET 312 help 313 Enable auditing infrastructure that can be used with another 314 kernel subsystem, such as SELinux (which requires this for 315 logging of avc messages output). System call auditing is included 316 on architectures which support it. 317 318config HAVE_ARCH_AUDITSYSCALL 319 bool 320 321config AUDITSYSCALL 322 def_bool y 323 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL 324 325config AUDIT_WATCH 326 def_bool y 327 depends on AUDITSYSCALL 328 select FSNOTIFY 329 330config AUDIT_TREE 331 def_bool y 332 depends on AUDITSYSCALL 333 select FSNOTIFY 334 335source "kernel/irq/Kconfig" 336source "kernel/time/Kconfig" 337 338menu "CPU/Task time and stats accounting" 339 340config VIRT_CPU_ACCOUNTING 341 bool 342 343choice 344 prompt "Cputime accounting" 345 default TICK_CPU_ACCOUNTING if !PPC64 346 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64 347 348# Kind of a stub config for the pure tick based cputime accounting 349config TICK_CPU_ACCOUNTING 350 bool "Simple tick based cputime accounting" 351 depends on !S390 && !NO_HZ_FULL 352 help 353 This is the basic tick based cputime accounting that maintains 354 statistics about user, system and idle time spent on per jiffies 355 granularity. 356 357 If unsure, say Y. 358 359config VIRT_CPU_ACCOUNTING_NATIVE 360 bool "Deterministic task and CPU time accounting" 361 depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL 362 select VIRT_CPU_ACCOUNTING 363 help 364 Select this option to enable more accurate task and CPU time 365 accounting. This is done by reading a CPU counter on each 366 kernel entry and exit and on transitions within the kernel 367 between system, softirq and hardirq state, so there is a 368 small performance impact. In the case of s390 or IBM POWER > 5, 369 this also enables accounting of stolen time on logically-partitioned 370 systems. 371 372config VIRT_CPU_ACCOUNTING_GEN 373 bool "Full dynticks CPU time accounting" 374 depends on HAVE_CONTEXT_TRACKING 375 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN 376 select VIRT_CPU_ACCOUNTING 377 select CONTEXT_TRACKING 378 help 379 Select this option to enable task and CPU time accounting on full 380 dynticks systems. This accounting is implemented by watching every 381 kernel-user boundaries using the context tracking subsystem. 382 The accounting is thus performed at the expense of some significant 383 overhead. 384 385 For now this is only useful if you are working on the full 386 dynticks subsystem development. 387 388 If unsure, say N. 389 390endchoice 391 392config IRQ_TIME_ACCOUNTING 393 bool "Fine granularity task level IRQ time accounting" 394 depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE 395 help 396 Select this option to enable fine granularity task irq time 397 accounting. This is done by reading a timestamp on each 398 transitions between softirq and hardirq state, so there can be a 399 small performance impact. 400 401 If in doubt, say N here. 402 403config BSD_PROCESS_ACCT 404 bool "BSD Process Accounting" 405 depends on MULTIUSER 406 help 407 If you say Y here, a user level program will be able to instruct the 408 kernel (via a special system call) to write process accounting 409 information to a file: whenever a process exits, information about 410 that process will be appended to the file by the kernel. The 411 information includes things such as creation time, owning user, 412 command name, memory usage, controlling terminal etc. (the complete 413 list is in the struct acct in <file:include/linux/acct.h>). It is 414 up to the user level program to do useful things with this 415 information. This is generally a good idea, so say Y. 416 417config BSD_PROCESS_ACCT_V3 418 bool "BSD Process Accounting version 3 file format" 419 depends on BSD_PROCESS_ACCT 420 default n 421 help 422 If you say Y here, the process accounting information is written 423 in a new file format that also logs the process IDs of each 424 process and it's parent. Note that this file format is incompatible 425 with previous v0/v1/v2 file formats, so you will need updated tools 426 for processing it. A preliminary version of these tools is available 427 at <http://www.gnu.org/software/acct/>. 428 429config TASKSTATS 430 bool "Export task/process statistics through netlink" 431 depends on NET 432 depends on MULTIUSER 433 default n 434 help 435 Export selected statistics for tasks/processes through the 436 generic netlink interface. Unlike BSD process accounting, the 437 statistics are available during the lifetime of tasks/processes as 438 responses to commands. Like BSD accounting, they are sent to user 439 space on task exit. 440 441 Say N if unsure. 442 443config TASK_DELAY_ACCT 444 bool "Enable per-task delay accounting" 445 depends on TASKSTATS 446 select SCHED_INFO 447 help 448 Collect information on time spent by a task waiting for system 449 resources like cpu, synchronous block I/O completion and swapping 450 in pages. Such statistics can help in setting a task's priorities 451 relative to other tasks for cpu, io, rss limits etc. 452 453 Say N if unsure. 454 455config TASK_XACCT 456 bool "Enable extended accounting over taskstats" 457 depends on TASKSTATS 458 help 459 Collect extended task accounting data and send the data 460 to userland for processing over the taskstats interface. 461 462 Say N if unsure. 463 464config TASK_IO_ACCOUNTING 465 bool "Enable per-task storage I/O accounting" 466 depends on TASK_XACCT 467 help 468 Collect information on the number of bytes of storage I/O which this 469 task has caused. 470 471 Say N if unsure. 472 473endmenu # "CPU/Task time and stats accounting" 474 475menu "RCU Subsystem" 476 477config TREE_RCU 478 bool 479 default y if !PREEMPT && SMP 480 help 481 This option selects the RCU implementation that is 482 designed for very large SMP system with hundreds or 483 thousands of CPUs. It also scales down nicely to 484 smaller systems. 485 486config PREEMPT_RCU 487 bool 488 default y if PREEMPT 489 help 490 This option selects the RCU implementation that is 491 designed for very large SMP systems with hundreds or 492 thousands of CPUs, but for which real-time response 493 is also required. It also scales down nicely to 494 smaller systems. 495 496 Select this option if you are unsure. 497 498config TINY_RCU 499 bool 500 default y if !PREEMPT && !SMP 501 help 502 This option selects the RCU implementation that is 503 designed for UP systems from which real-time response 504 is not required. This option greatly reduces the 505 memory footprint of RCU. 506 507config RCU_EXPERT 508 bool "Make expert-level adjustments to RCU configuration" 509 default n 510 help 511 This option needs to be enabled if you wish to make 512 expert-level adjustments to RCU configuration. By default, 513 no such adjustments can be made, which has the often-beneficial 514 side-effect of preventing "make oldconfig" from asking you all 515 sorts of detailed questions about how you would like numerous 516 obscure RCU options to be set up. 517 518 Say Y if you need to make expert-level adjustments to RCU. 519 520 Say N if you are unsure. 521 522config SRCU 523 bool 524 help 525 This option selects the sleepable version of RCU. This version 526 permits arbitrary sleeping or blocking within RCU read-side critical 527 sections. 528 529config TASKS_RCU 530 bool 531 default n 532 depends on !UML 533 select SRCU 534 help 535 This option enables a task-based RCU implementation that uses 536 only voluntary context switch (not preemption!), idle, and 537 user-mode execution as quiescent states. 538 539config RCU_STALL_COMMON 540 def_bool ( TREE_RCU || PREEMPT_RCU || RCU_TRACE ) 541 help 542 This option enables RCU CPU stall code that is common between 543 the TINY and TREE variants of RCU. The purpose is to allow 544 the tiny variants to disable RCU CPU stall warnings, while 545 making these warnings mandatory for the tree variants. 546 547config CONTEXT_TRACKING 548 bool 549 550config CONTEXT_TRACKING_FORCE 551 bool "Force context tracking" 552 depends on CONTEXT_TRACKING 553 default y if !NO_HZ_FULL 554 help 555 The major pre-requirement for full dynticks to work is to 556 support the context tracking subsystem. But there are also 557 other dependencies to provide in order to make the full 558 dynticks working. 559 560 This option stands for testing when an arch implements the 561 context tracking backend but doesn't yet fullfill all the 562 requirements to make the full dynticks feature working. 563 Without the full dynticks, there is no way to test the support 564 for context tracking and the subsystems that rely on it: RCU 565 userspace extended quiescent state and tickless cputime 566 accounting. This option copes with the absence of the full 567 dynticks subsystem by forcing the context tracking on all 568 CPUs in the system. 569 570 Say Y only if you're working on the development of an 571 architecture backend for the context tracking. 572 573 Say N otherwise, this option brings an overhead that you 574 don't want in production. 575 576 577config RCU_FANOUT 578 int "Tree-based hierarchical RCU fanout value" 579 range 2 64 if 64BIT 580 range 2 32 if !64BIT 581 depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT 582 default 64 if 64BIT 583 default 32 if !64BIT 584 help 585 This option controls the fanout of hierarchical implementations 586 of RCU, allowing RCU to work efficiently on machines with 587 large numbers of CPUs. This value must be at least the fourth 588 root of NR_CPUS, which allows NR_CPUS to be insanely large. 589 The default value of RCU_FANOUT should be used for production 590 systems, but if you are stress-testing the RCU implementation 591 itself, small RCU_FANOUT values allow you to test large-system 592 code paths on small(er) systems. 593 594 Select a specific number if testing RCU itself. 595 Take the default if unsure. 596 597config RCU_FANOUT_LEAF 598 int "Tree-based hierarchical RCU leaf-level fanout value" 599 range 2 64 if 64BIT 600 range 2 32 if !64BIT 601 depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT 602 default 16 603 help 604 This option controls the leaf-level fanout of hierarchical 605 implementations of RCU, and allows trading off cache misses 606 against lock contention. Systems that synchronize their 607 scheduling-clock interrupts for energy-efficiency reasons will 608 want the default because the smaller leaf-level fanout keeps 609 lock contention levels acceptably low. Very large systems 610 (hundreds or thousands of CPUs) will instead want to set this 611 value to the maximum value possible in order to reduce the 612 number of cache misses incurred during RCU's grace-period 613 initialization. These systems tend to run CPU-bound, and thus 614 are not helped by synchronized interrupts, and thus tend to 615 skew them, which reduces lock contention enough that large 616 leaf-level fanouts work well. 617 618 Select a specific number if testing RCU itself. 619 620 Select the maximum permissible value for large systems. 621 622 Take the default if unsure. 623 624config RCU_FAST_NO_HZ 625 bool "Accelerate last non-dyntick-idle CPU's grace periods" 626 depends on NO_HZ_COMMON && SMP && RCU_EXPERT 627 default n 628 help 629 This option permits CPUs to enter dynticks-idle state even if 630 they have RCU callbacks queued, and prevents RCU from waking 631 these CPUs up more than roughly once every four jiffies (by 632 default, you can adjust this using the rcutree.rcu_idle_gp_delay 633 parameter), thus improving energy efficiency. On the other 634 hand, this option increases the duration of RCU grace periods, 635 for example, slowing down synchronize_rcu(). 636 637 Say Y if energy efficiency is critically important, and you 638 don't care about increased grace-period durations. 639 640 Say N if you are unsure. 641 642config TREE_RCU_TRACE 643 def_bool RCU_TRACE && ( TREE_RCU || PREEMPT_RCU ) 644 select DEBUG_FS 645 help 646 This option provides tracing for the TREE_RCU and 647 PREEMPT_RCU implementations, permitting Makefile to 648 trivially select kernel/rcutree_trace.c. 649 650config RCU_BOOST 651 bool "Enable RCU priority boosting" 652 depends on RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT 653 default n 654 help 655 This option boosts the priority of preempted RCU readers that 656 block the current preemptible RCU grace period for too long. 657 This option also prevents heavy loads from blocking RCU 658 callback invocation for all flavors of RCU. 659 660 Say Y here if you are working with real-time apps or heavy loads 661 Say N here if you are unsure. 662 663config RCU_KTHREAD_PRIO 664 int "Real-time priority to use for RCU worker threads" 665 range 1 99 if RCU_BOOST 666 range 0 99 if !RCU_BOOST 667 default 1 if RCU_BOOST 668 default 0 if !RCU_BOOST 669 depends on RCU_EXPERT 670 help 671 This option specifies the SCHED_FIFO priority value that will be 672 assigned to the rcuc/n and rcub/n threads and is also the value 673 used for RCU_BOOST (if enabled). If you are working with a 674 real-time application that has one or more CPU-bound threads 675 running at a real-time priority level, you should set 676 RCU_KTHREAD_PRIO to a priority higher than the highest-priority 677 real-time CPU-bound application thread. The default RCU_KTHREAD_PRIO 678 value of 1 is appropriate in the common case, which is real-time 679 applications that do not have any CPU-bound threads. 680 681 Some real-time applications might not have a single real-time 682 thread that saturates a given CPU, but instead might have 683 multiple real-time threads that, taken together, fully utilize 684 that CPU. In this case, you should set RCU_KTHREAD_PRIO to 685 a priority higher than the lowest-priority thread that is 686 conspiring to prevent the CPU from running any non-real-time 687 tasks. For example, if one thread at priority 10 and another 688 thread at priority 5 are between themselves fully consuming 689 the CPU time on a given CPU, then RCU_KTHREAD_PRIO should be 690 set to priority 6 or higher. 691 692 Specify the real-time priority, or take the default if unsure. 693 694config RCU_BOOST_DELAY 695 int "Milliseconds to delay boosting after RCU grace-period start" 696 range 0 3000 697 depends on RCU_BOOST 698 default 500 699 help 700 This option specifies the time to wait after the beginning of 701 a given grace period before priority-boosting preempted RCU 702 readers blocking that grace period. Note that any RCU reader 703 blocking an expedited RCU grace period is boosted immediately. 704 705 Accept the default if unsure. 706 707config RCU_NOCB_CPU 708 bool "Offload RCU callback processing from boot-selected CPUs" 709 depends on TREE_RCU || PREEMPT_RCU 710 depends on RCU_EXPERT || NO_HZ_FULL 711 default n 712 help 713 Use this option to reduce OS jitter for aggressive HPC or 714 real-time workloads. It can also be used to offload RCU 715 callback invocation to energy-efficient CPUs in battery-powered 716 asymmetric multiprocessors. 717 718 This option offloads callback invocation from the set of 719 CPUs specified at boot time by the rcu_nocbs parameter. 720 For each such CPU, a kthread ("rcuox/N") will be created to 721 invoke callbacks, where the "N" is the CPU being offloaded, 722 and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and 723 "s" for RCU-sched. Nothing prevents this kthread from running 724 on the specified CPUs, but (1) the kthreads may be preempted 725 between each callback, and (2) affinity or cgroups can be used 726 to force the kthreads to run on whatever set of CPUs is desired. 727 728 Say Y here if you want to help to debug reduced OS jitter. 729 Say N here if you are unsure. 730 731choice 732 prompt "Build-forced no-CBs CPUs" 733 default RCU_NOCB_CPU_NONE 734 depends on RCU_NOCB_CPU 735 help 736 This option allows no-CBs CPUs (whose RCU callbacks are invoked 737 from kthreads rather than from softirq context) to be specified 738 at build time. Additional no-CBs CPUs may be specified by 739 the rcu_nocbs= boot parameter. 740 741config RCU_NOCB_CPU_NONE 742 bool "No build_forced no-CBs CPUs" 743 help 744 This option does not force any of the CPUs to be no-CBs CPUs. 745 Only CPUs designated by the rcu_nocbs= boot parameter will be 746 no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU 747 kthreads whose names begin with "rcuo". All other CPUs will 748 invoke their own RCU callbacks in softirq context. 749 750 Select this option if you want to choose no-CBs CPUs at 751 boot time, for example, to allow testing of different no-CBs 752 configurations without having to rebuild the kernel each time. 753 754config RCU_NOCB_CPU_ZERO 755 bool "CPU 0 is a build_forced no-CBs CPU" 756 help 757 This option forces CPU 0 to be a no-CBs CPU, so that its RCU 758 callbacks are invoked by a per-CPU kthread whose name begins 759 with "rcuo". Additional CPUs may be designated as no-CBs 760 CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs. 761 All other CPUs will invoke their own RCU callbacks in softirq 762 context. 763 764 Select this if CPU 0 needs to be a no-CBs CPU for real-time 765 or energy-efficiency reasons, but the real reason it exists 766 is to ensure that randconfig testing covers mixed systems. 767 768config RCU_NOCB_CPU_ALL 769 bool "All CPUs are build_forced no-CBs CPUs" 770 help 771 This option forces all CPUs to be no-CBs CPUs. The rcu_nocbs= 772 boot parameter will be ignored. All CPUs' RCU callbacks will 773 be executed in the context of per-CPU rcuo kthreads created for 774 this purpose. Assuming that the kthreads whose names start with 775 "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter 776 on the remaining CPUs, but might decrease memory locality during 777 RCU-callback invocation, thus potentially degrading throughput. 778 779 Select this if all CPUs need to be no-CBs CPUs for real-time 780 or energy-efficiency reasons. 781 782endchoice 783 784config RCU_EXPEDITE_BOOT 785 bool 786 default n 787 help 788 This option enables expedited grace periods at boot time, 789 as if rcu_expedite_gp() had been invoked early in boot. 790 The corresponding rcu_unexpedite_gp() is invoked from 791 rcu_end_inkernel_boot(), which is intended to be invoked 792 at the end of the kernel-only boot sequence, just before 793 init is exec'ed. 794 795 Accept the default if unsure. 796 797endmenu # "RCU Subsystem" 798 799config BUILD_BIN2C 800 bool 801 default n 802 803config IKCONFIG 804 tristate "Kernel .config support" 805 select BUILD_BIN2C 806 ---help--- 807 This option enables the complete Linux kernel ".config" file 808 contents to be saved in the kernel. It provides documentation 809 of which kernel options are used in a running kernel or in an 810 on-disk kernel. This information can be extracted from the kernel 811 image file with the script scripts/extract-ikconfig and used as 812 input to rebuild the current kernel or to build another kernel. 813 It can also be extracted from a running kernel by reading 814 /proc/config.gz if enabled (below). 815 816config IKCONFIG_PROC 817 bool "Enable access to .config through /proc/config.gz" 818 depends on IKCONFIG && PROC_FS 819 ---help--- 820 This option enables access to the kernel configuration file 821 through /proc/config.gz. 822 823config LOG_BUF_SHIFT 824 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)" 825 range 12 25 826 default 17 827 depends on PRINTK 828 help 829 Select the minimal kernel log buffer size as a power of 2. 830 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config 831 parameter, see below. Any higher size also might be forced 832 by "log_buf_len" boot parameter. 833 834 Examples: 835 17 => 128 KB 836 16 => 64 KB 837 15 => 32 KB 838 14 => 16 KB 839 13 => 8 KB 840 12 => 4 KB 841 842config LOG_CPU_MAX_BUF_SHIFT 843 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)" 844 depends on SMP 845 range 0 21 846 default 12 if !BASE_SMALL 847 default 0 if BASE_SMALL 848 depends on PRINTK 849 help 850 This option allows to increase the default ring buffer size 851 according to the number of CPUs. The value defines the contribution 852 of each CPU as a power of 2. The used space is typically only few 853 lines however it might be much more when problems are reported, 854 e.g. backtraces. 855 856 The increased size means that a new buffer has to be allocated and 857 the original static one is unused. It makes sense only on systems 858 with more CPUs. Therefore this value is used only when the sum of 859 contributions is greater than the half of the default kernel ring 860 buffer as defined by LOG_BUF_SHIFT. The default values are set 861 so that more than 64 CPUs are needed to trigger the allocation. 862 863 Also this option is ignored when "log_buf_len" kernel parameter is 864 used as it forces an exact (power of two) size of the ring buffer. 865 866 The number of possible CPUs is used for this computation ignoring 867 hotplugging making the computation optimal for the worst case 868 scenario while allowing a simple algorithm to be used from bootup. 869 870 Examples shift values and their meaning: 871 17 => 128 KB for each CPU 872 16 => 64 KB for each CPU 873 15 => 32 KB for each CPU 874 14 => 16 KB for each CPU 875 13 => 8 KB for each CPU 876 12 => 4 KB for each CPU 877 878config NMI_LOG_BUF_SHIFT 879 int "Temporary per-CPU NMI log buffer size (12 => 4KB, 13 => 8KB)" 880 range 10 21 881 default 13 882 depends on PRINTK_NMI 883 help 884 Select the size of a per-CPU buffer where NMI messages are temporary 885 stored. They are copied to the main log buffer in a safe context 886 to avoid a deadlock. The value defines the size as a power of 2. 887 888 NMI messages are rare and limited. The largest one is when 889 a backtrace is printed. It usually fits into 4KB. Select 890 8KB if you want to be on the safe side. 891 892 Examples: 893 17 => 128 KB for each CPU 894 16 => 64 KB for each CPU 895 15 => 32 KB for each CPU 896 14 => 16 KB for each CPU 897 13 => 8 KB for each CPU 898 12 => 4 KB for each CPU 899 900# 901# Architectures with an unreliable sched_clock() should select this: 902# 903config HAVE_UNSTABLE_SCHED_CLOCK 904 bool 905 906config GENERIC_SCHED_CLOCK 907 bool 908 909# 910# For architectures that want to enable the support for NUMA-affine scheduler 911# balancing logic: 912# 913config ARCH_SUPPORTS_NUMA_BALANCING 914 bool 915 916# 917# For architectures that prefer to flush all TLBs after a number of pages 918# are unmapped instead of sending one IPI per page to flush. The architecture 919# must provide guarantees on what happens if a clean TLB cache entry is 920# written after the unmap. Details are in mm/rmap.c near the check for 921# should_defer_flush. The architecture should also consider if the full flush 922# and the refill costs are offset by the savings of sending fewer IPIs. 923config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH 924 bool 925 926# 927# For architectures that know their GCC __int128 support is sound 928# 929config ARCH_SUPPORTS_INT128 930 bool 931 932# For architectures that (ab)use NUMA to represent different memory regions 933# all cpu-local but of different latencies, such as SuperH. 934# 935config ARCH_WANT_NUMA_VARIABLE_LOCALITY 936 bool 937 938config NUMA_BALANCING 939 bool "Memory placement aware NUMA scheduler" 940 depends on ARCH_SUPPORTS_NUMA_BALANCING 941 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY 942 depends on SMP && NUMA && MIGRATION 943 help 944 This option adds support for automatic NUMA aware memory/task placement. 945 The mechanism is quite primitive and is based on migrating memory when 946 it has references to the node the task is running on. 947 948 This system will be inactive on UMA systems. 949 950config NUMA_BALANCING_DEFAULT_ENABLED 951 bool "Automatically enable NUMA aware memory/task placement" 952 default y 953 depends on NUMA_BALANCING 954 help 955 If set, automatic NUMA balancing will be enabled if running on a NUMA 956 machine. 957 958menuconfig CGROUPS 959 bool "Control Group support" 960 select KERNFS 961 help 962 This option adds support for grouping sets of processes together, for 963 use with process control subsystems such as Cpusets, CFS, memory 964 controls or device isolation. 965 See 966 - Documentation/scheduler/sched-design-CFS.txt (CFS) 967 - Documentation/cgroup-v1/ (features for grouping, isolation 968 and resource control) 969 970 Say N if unsure. 971 972if CGROUPS 973 974config PAGE_COUNTER 975 bool 976 977config MEMCG 978 bool "Memory controller" 979 select PAGE_COUNTER 980 select EVENTFD 981 help 982 Provides control over the memory footprint of tasks in a cgroup. 983 984config MEMCG_SWAP 985 bool "Swap controller" 986 depends on MEMCG && SWAP 987 help 988 Provides control over the swap space consumed by tasks in a cgroup. 989 990config MEMCG_SWAP_ENABLED 991 bool "Swap controller enabled by default" 992 depends on MEMCG_SWAP 993 default y 994 help 995 Memory Resource Controller Swap Extension comes with its price in 996 a bigger memory consumption. General purpose distribution kernels 997 which want to enable the feature but keep it disabled by default 998 and let the user enable it by swapaccount=1 boot command line 999 parameter should have this option unselected. 1000 For those who want to have the feature enabled by default should 1001 select this option (if, for some reason, they need to disable it 1002 then swapaccount=0 does the trick). 1003 1004config BLK_CGROUP 1005 bool "IO controller" 1006 depends on BLOCK 1007 default n 1008 ---help--- 1009 Generic block IO controller cgroup interface. This is the common 1010 cgroup interface which should be used by various IO controlling 1011 policies. 1012 1013 Currently, CFQ IO scheduler uses it to recognize task groups and 1014 control disk bandwidth allocation (proportional time slice allocation) 1015 to such task groups. It is also used by bio throttling logic in 1016 block layer to implement upper limit in IO rates on a device. 1017 1018 This option only enables generic Block IO controller infrastructure. 1019 One needs to also enable actual IO controlling logic/policy. For 1020 enabling proportional weight division of disk bandwidth in CFQ, set 1021 CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set 1022 CONFIG_BLK_DEV_THROTTLING=y. 1023 1024 See Documentation/cgroup-v1/blkio-controller.txt for more information. 1025 1026config DEBUG_BLK_CGROUP 1027 bool "IO controller debugging" 1028 depends on BLK_CGROUP 1029 default n 1030 ---help--- 1031 Enable some debugging help. Currently it exports additional stat 1032 files in a cgroup which can be useful for debugging. 1033 1034config CGROUP_WRITEBACK 1035 bool 1036 depends on MEMCG && BLK_CGROUP 1037 default y 1038 1039menuconfig CGROUP_SCHED 1040 bool "CPU controller" 1041 default n 1042 help 1043 This feature lets CPU scheduler recognize task groups and control CPU 1044 bandwidth allocation to such task groups. It uses cgroups to group 1045 tasks. 1046 1047if CGROUP_SCHED 1048config FAIR_GROUP_SCHED 1049 bool "Group scheduling for SCHED_OTHER" 1050 depends on CGROUP_SCHED 1051 default CGROUP_SCHED 1052 1053config CFS_BANDWIDTH 1054 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED" 1055 depends on FAIR_GROUP_SCHED 1056 default n 1057 help 1058 This option allows users to define CPU bandwidth rates (limits) for 1059 tasks running within the fair group scheduler. Groups with no limit 1060 set are considered to be unconstrained and will run with no 1061 restriction. 1062 See tip/Documentation/scheduler/sched-bwc.txt for more information. 1063 1064config RT_GROUP_SCHED 1065 bool "Group scheduling for SCHED_RR/FIFO" 1066 depends on CGROUP_SCHED 1067 default n 1068 help 1069 This feature lets you explicitly allocate real CPU bandwidth 1070 to task groups. If enabled, it will also make it impossible to 1071 schedule realtime tasks for non-root users until you allocate 1072 realtime bandwidth for them. 1073 See Documentation/scheduler/sched-rt-group.txt for more information. 1074 1075endif #CGROUP_SCHED 1076 1077config CGROUP_PIDS 1078 bool "PIDs controller" 1079 help 1080 Provides enforcement of process number limits in the scope of a 1081 cgroup. Any attempt to fork more processes than is allowed in the 1082 cgroup will fail. PIDs are fundamentally a global resource because it 1083 is fairly trivial to reach PID exhaustion before you reach even a 1084 conservative kmemcg limit. As a result, it is possible to grind a 1085 system to halt without being limited by other cgroup policies. The 1086 PIDs controller is designed to stop this from happening. 1087 1088 It should be noted that organisational operations (such as attaching 1089 to a cgroup hierarchy will *not* be blocked by the PIDs controller), 1090 since the PIDs limit only affects a process's ability to fork, not to 1091 attach to a cgroup. 1092 1093config CGROUP_FREEZER 1094 bool "Freezer controller" 1095 help 1096 Provides a way to freeze and unfreeze all tasks in a 1097 cgroup. 1098 1099 This option affects the ORIGINAL cgroup interface. The cgroup2 memory 1100 controller includes important in-kernel memory consumers per default. 1101 1102 If you're using cgroup2, say N. 1103 1104config CGROUP_HUGETLB 1105 bool "HugeTLB controller" 1106 depends on HUGETLB_PAGE 1107 select PAGE_COUNTER 1108 default n 1109 help 1110 Provides a cgroup controller for HugeTLB pages. 1111 When you enable this, you can put a per cgroup limit on HugeTLB usage. 1112 The limit is enforced during page fault. Since HugeTLB doesn't 1113 support page reclaim, enforcing the limit at page fault time implies 1114 that, the application will get SIGBUS signal if it tries to access 1115 HugeTLB pages beyond its limit. This requires the application to know 1116 beforehand how much HugeTLB pages it would require for its use. The 1117 control group is tracked in the third page lru pointer. This means 1118 that we cannot use the controller with huge page less than 3 pages. 1119 1120config CPUSETS 1121 bool "Cpuset controller" 1122 help 1123 This option will let you create and manage CPUSETs which 1124 allow dynamically partitioning a system into sets of CPUs and 1125 Memory Nodes and assigning tasks to run only within those sets. 1126 This is primarily useful on large SMP or NUMA systems. 1127 1128 Say N if unsure. 1129 1130config PROC_PID_CPUSET 1131 bool "Include legacy /proc/<pid>/cpuset file" 1132 depends on CPUSETS 1133 default y 1134 1135config CGROUP_DEVICE 1136 bool "Device controller" 1137 help 1138 Provides a cgroup controller implementing whitelists for 1139 devices which a process in the cgroup can mknod or open. 1140 1141config CGROUP_CPUACCT 1142 bool "Simple CPU accounting controller" 1143 help 1144 Provides a simple controller for monitoring the 1145 total CPU consumed by the tasks in a cgroup. 1146 1147config CGROUP_PERF 1148 bool "Perf controller" 1149 depends on PERF_EVENTS 1150 help 1151 This option extends the perf per-cpu mode to restrict monitoring 1152 to threads which belong to the cgroup specified and run on the 1153 designated cpu. 1154 1155 Say N if unsure. 1156 1157config CGROUP_BPF 1158 bool "Support for eBPF programs attached to cgroups" 1159 depends on BPF_SYSCALL 1160 select SOCK_CGROUP_DATA 1161 help 1162 Allow attaching eBPF programs to a cgroup using the bpf(2) 1163 syscall command BPF_PROG_ATTACH. 1164 1165 In which context these programs are accessed depends on the type 1166 of attachment. For instance, programs that are attached using 1167 BPF_CGROUP_INET_INGRESS will be executed on the ingress path of 1168 inet sockets. 1169 1170config CGROUP_DEBUG 1171 bool "Example controller" 1172 default n 1173 help 1174 This option enables a simple controller that exports 1175 debugging information about the cgroups framework. 1176 1177 Say N. 1178 1179config SOCK_CGROUP_DATA 1180 bool 1181 default n 1182 1183endif # CGROUPS 1184 1185config CHECKPOINT_RESTORE 1186 bool "Checkpoint/restore support" if EXPERT 1187 select PROC_CHILDREN 1188 default n 1189 help 1190 Enables additional kernel features in a sake of checkpoint/restore. 1191 In particular it adds auxiliary prctl codes to setup process text, 1192 data and heap segment sizes, and a few additional /proc filesystem 1193 entries. 1194 1195 If unsure, say N here. 1196 1197menuconfig NAMESPACES 1198 bool "Namespaces support" if EXPERT 1199 depends on MULTIUSER 1200 default !EXPERT 1201 help 1202 Provides the way to make tasks work with different objects using 1203 the same id. For example same IPC id may refer to different objects 1204 or same user id or pid may refer to different tasks when used in 1205 different namespaces. 1206 1207if NAMESPACES 1208 1209config UTS_NS 1210 bool "UTS namespace" 1211 default y 1212 help 1213 In this namespace tasks see different info provided with the 1214 uname() system call 1215 1216config IPC_NS 1217 bool "IPC namespace" 1218 depends on (SYSVIPC || POSIX_MQUEUE) 1219 default y 1220 help 1221 In this namespace tasks work with IPC ids which correspond to 1222 different IPC objects in different namespaces. 1223 1224config USER_NS 1225 bool "User namespace" 1226 default n 1227 help 1228 This allows containers, i.e. vservers, to use user namespaces 1229 to provide different user info for different servers. 1230 1231 When user namespaces are enabled in the kernel it is 1232 recommended that the MEMCG option also be enabled and that 1233 user-space use the memory control groups to limit the amount 1234 of memory a memory unprivileged users can use. 1235 1236 If unsure, say N. 1237 1238config PID_NS 1239 bool "PID Namespaces" 1240 default y 1241 help 1242 Support process id namespaces. This allows having multiple 1243 processes with the same pid as long as they are in different 1244 pid namespaces. This is a building block of containers. 1245 1246config NET_NS 1247 bool "Network namespace" 1248 depends on NET 1249 default y 1250 help 1251 Allow user space to create what appear to be multiple instances 1252 of the network stack. 1253 1254endif # NAMESPACES 1255 1256config SCHED_AUTOGROUP 1257 bool "Automatic process group scheduling" 1258 select CGROUPS 1259 select CGROUP_SCHED 1260 select FAIR_GROUP_SCHED 1261 help 1262 This option optimizes the scheduler for common desktop workloads by 1263 automatically creating and populating task groups. This separation 1264 of workloads isolates aggressive CPU burners (like build jobs) from 1265 desktop applications. Task group autogeneration is currently based 1266 upon task session. 1267 1268config SYSFS_DEPRECATED 1269 bool "Enable deprecated sysfs features to support old userspace tools" 1270 depends on SYSFS 1271 default n 1272 help 1273 This option adds code that switches the layout of the "block" class 1274 devices, to not show up in /sys/class/block/, but only in 1275 /sys/block/. 1276 1277 This switch is only active when the sysfs.deprecated=1 boot option is 1278 passed or the SYSFS_DEPRECATED_V2 option is set. 1279 1280 This option allows new kernels to run on old distributions and tools, 1281 which might get confused by /sys/class/block/. Since 2007/2008 all 1282 major distributions and tools handle this just fine. 1283 1284 Recent distributions and userspace tools after 2009/2010 depend on 1285 the existence of /sys/class/block/, and will not work with this 1286 option enabled. 1287 1288 Only if you are using a new kernel on an old distribution, you might 1289 need to say Y here. 1290 1291config SYSFS_DEPRECATED_V2 1292 bool "Enable deprecated sysfs features by default" 1293 default n 1294 depends on SYSFS 1295 depends on SYSFS_DEPRECATED 1296 help 1297 Enable deprecated sysfs by default. 1298 1299 See the CONFIG_SYSFS_DEPRECATED option for more details about this 1300 option. 1301 1302 Only if you are using a new kernel on an old distribution, you might 1303 need to say Y here. Even then, odds are you would not need it 1304 enabled, you can always pass the boot option if absolutely necessary. 1305 1306config RELAY 1307 bool "Kernel->user space relay support (formerly relayfs)" 1308 select IRQ_WORK 1309 help 1310 This option enables support for relay interface support in 1311 certain file systems (such as debugfs). 1312 It is designed to provide an efficient mechanism for tools and 1313 facilities to relay large amounts of data from kernel space to 1314 user space. 1315 1316 If unsure, say N. 1317 1318config BLK_DEV_INITRD 1319 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support" 1320 depends on BROKEN || !FRV 1321 help 1322 The initial RAM filesystem is a ramfs which is loaded by the 1323 boot loader (loadlin or lilo) and that is mounted as root 1324 before the normal boot procedure. It is typically used to 1325 load modules needed to mount the "real" root file system, 1326 etc. See <file:Documentation/admin-guide/initrd.rst> for details. 1327 1328 If RAM disk support (BLK_DEV_RAM) is also included, this 1329 also enables initial RAM disk (initrd) support and adds 1330 15 Kbytes (more on some other architectures) to the kernel size. 1331 1332 If unsure say Y. 1333 1334if BLK_DEV_INITRD 1335 1336source "usr/Kconfig" 1337 1338endif 1339 1340choice 1341 prompt "Compiler optimization level" 1342 default CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE 1343 1344config CC_OPTIMIZE_FOR_PERFORMANCE 1345 bool "Optimize for performance" 1346 help 1347 This is the default optimization level for the kernel, building 1348 with the "-O2" compiler flag for best performance and most 1349 helpful compile-time warnings. 1350 1351config CC_OPTIMIZE_FOR_SIZE 1352 bool "Optimize for size" 1353 help 1354 Enabling this option will pass "-Os" instead of "-O2" to 1355 your compiler resulting in a smaller kernel. 1356 1357 If unsure, say N. 1358 1359endchoice 1360 1361config SYSCTL 1362 bool 1363 1364config ANON_INODES 1365 bool 1366 1367config HAVE_UID16 1368 bool 1369 1370config SYSCTL_EXCEPTION_TRACE 1371 bool 1372 help 1373 Enable support for /proc/sys/debug/exception-trace. 1374 1375config SYSCTL_ARCH_UNALIGN_NO_WARN 1376 bool 1377 help 1378 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap 1379 Allows arch to define/use @no_unaligned_warning to possibly warn 1380 about unaligned access emulation going on under the hood. 1381 1382config SYSCTL_ARCH_UNALIGN_ALLOW 1383 bool 1384 help 1385 Enable support for /proc/sys/kernel/unaligned-trap 1386 Allows arches to define/use @unaligned_enabled to runtime toggle 1387 the unaligned access emulation. 1388 see arch/parisc/kernel/unaligned.c for reference 1389 1390config HAVE_PCSPKR_PLATFORM 1391 bool 1392 1393# interpreter that classic socket filters depend on 1394config BPF 1395 bool 1396 1397menuconfig EXPERT 1398 bool "Configure standard kernel features (expert users)" 1399 # Unhide debug options, to make the on-by-default options visible 1400 select DEBUG_KERNEL 1401 help 1402 This option allows certain base kernel options and settings 1403 to be disabled or tweaked. This is for specialized 1404 environments which can tolerate a "non-standard" kernel. 1405 Only use this if you really know what you are doing. 1406 1407config UID16 1408 bool "Enable 16-bit UID system calls" if EXPERT 1409 depends on HAVE_UID16 && MULTIUSER 1410 default y 1411 help 1412 This enables the legacy 16-bit UID syscall wrappers. 1413 1414config MULTIUSER 1415 bool "Multiple users, groups and capabilities support" if EXPERT 1416 default y 1417 help 1418 This option enables support for non-root users, groups and 1419 capabilities. 1420 1421 If you say N here, all processes will run with UID 0, GID 0, and all 1422 possible capabilities. Saying N here also compiles out support for 1423 system calls related to UIDs, GIDs, and capabilities, such as setuid, 1424 setgid, and capset. 1425 1426 If unsure, say Y here. 1427 1428config SGETMASK_SYSCALL 1429 bool "sgetmask/ssetmask syscalls support" if EXPERT 1430 def_bool PARISC || MN10300 || BLACKFIN || M68K || PPC || MIPS || X86 || SPARC || CRIS || MICROBLAZE || SUPERH 1431 ---help--- 1432 sys_sgetmask and sys_ssetmask are obsolete system calls 1433 no longer supported in libc but still enabled by default in some 1434 architectures. 1435 1436 If unsure, leave the default option here. 1437 1438config SYSFS_SYSCALL 1439 bool "Sysfs syscall support" if EXPERT 1440 default y 1441 ---help--- 1442 sys_sysfs is an obsolete system call no longer supported in libc. 1443 Note that disabling this option is more secure but might break 1444 compatibility with some systems. 1445 1446 If unsure say Y here. 1447 1448config SYSCTL_SYSCALL 1449 bool "Sysctl syscall support" if EXPERT 1450 depends on PROC_SYSCTL 1451 default n 1452 select SYSCTL 1453 ---help--- 1454 sys_sysctl uses binary paths that have been found challenging 1455 to properly maintain and use. The interface in /proc/sys 1456 using paths with ascii names is now the primary path to this 1457 information. 1458 1459 Almost nothing using the binary sysctl interface so if you are 1460 trying to save some space it is probably safe to disable this, 1461 making your kernel marginally smaller. 1462 1463 If unsure say N here. 1464 1465config POSIX_TIMERS 1466 bool "Posix Clocks & timers" if EXPERT 1467 default y 1468 help 1469 This includes native support for POSIX timers to the kernel. 1470 Some embedded systems have no use for them and therefore they 1471 can be configured out to reduce the size of the kernel image. 1472 1473 When this option is disabled, the following syscalls won't be 1474 available: timer_create, timer_gettime: timer_getoverrun, 1475 timer_settime, timer_delete, clock_adjtime, getitimer, 1476 setitimer, alarm. Furthermore, the clock_settime, clock_gettime, 1477 clock_getres and clock_nanosleep syscalls will be limited to 1478 CLOCK_REALTIME, CLOCK_MONOTONIC and CLOCK_BOOTTIME only. 1479 1480 If unsure say y. 1481 1482config KALLSYMS 1483 bool "Load all symbols for debugging/ksymoops" if EXPERT 1484 default y 1485 help 1486 Say Y here to let the kernel print out symbolic crash information and 1487 symbolic stack backtraces. This increases the size of the kernel 1488 somewhat, as all symbols have to be loaded into the kernel image. 1489 1490config KALLSYMS_ALL 1491 bool "Include all symbols in kallsyms" 1492 depends on DEBUG_KERNEL && KALLSYMS 1493 help 1494 Normally kallsyms only contains the symbols of functions for nicer 1495 OOPS messages and backtraces (i.e., symbols from the text and inittext 1496 sections). This is sufficient for most cases. And only in very rare 1497 cases (e.g., when a debugger is used) all symbols are required (e.g., 1498 names of variables from the data sections, etc). 1499 1500 This option makes sure that all symbols are loaded into the kernel 1501 image (i.e., symbols from all sections) in cost of increased kernel 1502 size (depending on the kernel configuration, it may be 300KiB or 1503 something like this). 1504 1505 Say N unless you really need all symbols. 1506 1507config KALLSYMS_ABSOLUTE_PERCPU 1508 bool 1509 depends on KALLSYMS 1510 default X86_64 && SMP 1511 1512config KALLSYMS_BASE_RELATIVE 1513 bool 1514 depends on KALLSYMS 1515 default !IA64 && !(TILE && 64BIT) 1516 help 1517 Instead of emitting them as absolute values in the native word size, 1518 emit the symbol references in the kallsyms table as 32-bit entries, 1519 each containing a relative value in the range [base, base + U32_MAX] 1520 or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either 1521 an absolute value in the range [0, S32_MAX] or a relative value in the 1522 range [base, base + S32_MAX], where base is the lowest relative symbol 1523 address encountered in the image. 1524 1525 On 64-bit builds, this reduces the size of the address table by 50%, 1526 but more importantly, it results in entries whose values are build 1527 time constants, and no relocation pass is required at runtime to fix 1528 up the entries based on the runtime load address of the kernel. 1529 1530config PRINTK 1531 default y 1532 bool "Enable support for printk" if EXPERT 1533 select IRQ_WORK 1534 help 1535 This option enables normal printk support. Removing it 1536 eliminates most of the message strings from the kernel image 1537 and makes the kernel more or less silent. As this makes it 1538 very difficult to diagnose system problems, saying N here is 1539 strongly discouraged. 1540 1541config PRINTK_NMI 1542 def_bool y 1543 depends on PRINTK 1544 depends on HAVE_NMI 1545 1546config BUG 1547 bool "BUG() support" if EXPERT 1548 default y 1549 help 1550 Disabling this option eliminates support for BUG and WARN, reducing 1551 the size of your kernel image and potentially quietly ignoring 1552 numerous fatal conditions. You should only consider disabling this 1553 option for embedded systems with no facilities for reporting errors. 1554 Just say Y. 1555 1556config ELF_CORE 1557 depends on COREDUMP 1558 default y 1559 bool "Enable ELF core dumps" if EXPERT 1560 help 1561 Enable support for generating core dumps. Disabling saves about 4k. 1562 1563 1564config PCSPKR_PLATFORM 1565 bool "Enable PC-Speaker support" if EXPERT 1566 depends on HAVE_PCSPKR_PLATFORM 1567 select I8253_LOCK 1568 default y 1569 help 1570 This option allows to disable the internal PC-Speaker 1571 support, saving some memory. 1572 1573config BASE_FULL 1574 default y 1575 bool "Enable full-sized data structures for core" if EXPERT 1576 help 1577 Disabling this option reduces the size of miscellaneous core 1578 kernel data structures. This saves memory on small machines, 1579 but may reduce performance. 1580 1581config FUTEX 1582 bool "Enable futex support" if EXPERT 1583 default y 1584 select RT_MUTEXES 1585 help 1586 Disabling this option will cause the kernel to be built without 1587 support for "fast userspace mutexes". The resulting kernel may not 1588 run glibc-based applications correctly. 1589 1590config HAVE_FUTEX_CMPXCHG 1591 bool 1592 depends on FUTEX 1593 help 1594 Architectures should select this if futex_atomic_cmpxchg_inatomic() 1595 is implemented and always working. This removes a couple of runtime 1596 checks. 1597 1598config EPOLL 1599 bool "Enable eventpoll support" if EXPERT 1600 default y 1601 select ANON_INODES 1602 help 1603 Disabling this option will cause the kernel to be built without 1604 support for epoll family of system calls. 1605 1606config SIGNALFD 1607 bool "Enable signalfd() system call" if EXPERT 1608 select ANON_INODES 1609 default y 1610 help 1611 Enable the signalfd() system call that allows to receive signals 1612 on a file descriptor. 1613 1614 If unsure, say Y. 1615 1616config TIMERFD 1617 bool "Enable timerfd() system call" if EXPERT 1618 select ANON_INODES 1619 default y 1620 help 1621 Enable the timerfd() system call that allows to receive timer 1622 events on a file descriptor. 1623 1624 If unsure, say Y. 1625 1626config EVENTFD 1627 bool "Enable eventfd() system call" if EXPERT 1628 select ANON_INODES 1629 default y 1630 help 1631 Enable the eventfd() system call that allows to receive both 1632 kernel notification (ie. KAIO) or userspace notifications. 1633 1634 If unsure, say Y. 1635 1636# syscall, maps, verifier 1637config BPF_SYSCALL 1638 bool "Enable bpf() system call" 1639 select ANON_INODES 1640 select BPF 1641 default n 1642 help 1643 Enable the bpf() system call that allows to manipulate eBPF 1644 programs and maps via file descriptors. 1645 1646config SHMEM 1647 bool "Use full shmem filesystem" if EXPERT 1648 default y 1649 depends on MMU 1650 help 1651 The shmem is an internal filesystem used to manage shared memory. 1652 It is backed by swap and manages resource limits. It is also exported 1653 to userspace as tmpfs if TMPFS is enabled. Disabling this 1654 option replaces shmem and tmpfs with the much simpler ramfs code, 1655 which may be appropriate on small systems without swap. 1656 1657config AIO 1658 bool "Enable AIO support" if EXPERT 1659 default y 1660 help 1661 This option enables POSIX asynchronous I/O which may by used 1662 by some high performance threaded applications. Disabling 1663 this option saves about 7k. 1664 1665config ADVISE_SYSCALLS 1666 bool "Enable madvise/fadvise syscalls" if EXPERT 1667 default y 1668 help 1669 This option enables the madvise and fadvise syscalls, used by 1670 applications to advise the kernel about their future memory or file 1671 usage, improving performance. If building an embedded system where no 1672 applications use these syscalls, you can disable this option to save 1673 space. 1674 1675config USERFAULTFD 1676 bool "Enable userfaultfd() system call" 1677 select ANON_INODES 1678 depends on MMU 1679 help 1680 Enable the userfaultfd() system call that allows to intercept and 1681 handle page faults in userland. 1682 1683config PCI_QUIRKS 1684 default y 1685 bool "Enable PCI quirk workarounds" if EXPERT 1686 depends on PCI 1687 help 1688 This enables workarounds for various PCI chipset 1689 bugs/quirks. Disable this only if your target machine is 1690 unaffected by PCI quirks. 1691 1692config MEMBARRIER 1693 bool "Enable membarrier() system call" if EXPERT 1694 default y 1695 help 1696 Enable the membarrier() system call that allows issuing memory 1697 barriers across all running threads, which can be used to distribute 1698 the cost of user-space memory barriers asymmetrically by transforming 1699 pairs of memory barriers into pairs consisting of membarrier() and a 1700 compiler barrier. 1701 1702 If unsure, say Y. 1703 1704config EMBEDDED 1705 bool "Embedded system" 1706 option allnoconfig_y 1707 select EXPERT 1708 help 1709 This option should be enabled if compiling the kernel for 1710 an embedded system so certain expert options are available 1711 for configuration. 1712 1713config HAVE_PERF_EVENTS 1714 bool 1715 help 1716 See tools/perf/design.txt for details. 1717 1718config PERF_USE_VMALLOC 1719 bool 1720 help 1721 See tools/perf/design.txt for details 1722 1723menu "Kernel Performance Events And Counters" 1724 1725config PERF_EVENTS 1726 bool "Kernel performance events and counters" 1727 default y if PROFILING 1728 depends on HAVE_PERF_EVENTS 1729 select ANON_INODES 1730 select IRQ_WORK 1731 select SRCU 1732 help 1733 Enable kernel support for various performance events provided 1734 by software and hardware. 1735 1736 Software events are supported either built-in or via the 1737 use of generic tracepoints. 1738 1739 Most modern CPUs support performance events via performance 1740 counter registers. These registers count the number of certain 1741 types of hw events: such as instructions executed, cachemisses 1742 suffered, or branches mis-predicted - without slowing down the 1743 kernel or applications. These registers can also trigger interrupts 1744 when a threshold number of events have passed - and can thus be 1745 used to profile the code that runs on that CPU. 1746 1747 The Linux Performance Event subsystem provides an abstraction of 1748 these software and hardware event capabilities, available via a 1749 system call and used by the "perf" utility in tools/perf/. It 1750 provides per task and per CPU counters, and it provides event 1751 capabilities on top of those. 1752 1753 Say Y if unsure. 1754 1755config DEBUG_PERF_USE_VMALLOC 1756 default n 1757 bool "Debug: use vmalloc to back perf mmap() buffers" 1758 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC 1759 select PERF_USE_VMALLOC 1760 help 1761 Use vmalloc memory to back perf mmap() buffers. 1762 1763 Mostly useful for debugging the vmalloc code on platforms 1764 that don't require it. 1765 1766 Say N if unsure. 1767 1768endmenu 1769 1770config VM_EVENT_COUNTERS 1771 default y 1772 bool "Enable VM event counters for /proc/vmstat" if EXPERT 1773 help 1774 VM event counters are needed for event counts to be shown. 1775 This option allows the disabling of the VM event counters 1776 on EXPERT systems. /proc/vmstat will only show page counts 1777 if VM event counters are disabled. 1778 1779config SLUB_DEBUG 1780 default y 1781 bool "Enable SLUB debugging support" if EXPERT 1782 depends on SLUB && SYSFS 1783 help 1784 SLUB has extensive debug support features. Disabling these can 1785 result in significant savings in code size. This also disables 1786 SLUB sysfs support. /sys/slab will not exist and there will be 1787 no support for cache validation etc. 1788 1789config COMPAT_BRK 1790 bool "Disable heap randomization" 1791 default y 1792 help 1793 Randomizing heap placement makes heap exploits harder, but it 1794 also breaks ancient binaries (including anything libc5 based). 1795 This option changes the bootup default to heap randomization 1796 disabled, and can be overridden at runtime by setting 1797 /proc/sys/kernel/randomize_va_space to 2. 1798 1799 On non-ancient distros (post-2000 ones) N is usually a safe choice. 1800 1801choice 1802 prompt "Choose SLAB allocator" 1803 default SLUB 1804 help 1805 This option allows to select a slab allocator. 1806 1807config SLAB 1808 bool "SLAB" 1809 select HAVE_HARDENED_USERCOPY_ALLOCATOR 1810 help 1811 The regular slab allocator that is established and known to work 1812 well in all environments. It organizes cache hot objects in 1813 per cpu and per node queues. 1814 1815config SLUB 1816 bool "SLUB (Unqueued Allocator)" 1817 select HAVE_HARDENED_USERCOPY_ALLOCATOR 1818 help 1819 SLUB is a slab allocator that minimizes cache line usage 1820 instead of managing queues of cached objects (SLAB approach). 1821 Per cpu caching is realized using slabs of objects instead 1822 of queues of objects. SLUB can use memory efficiently 1823 and has enhanced diagnostics. SLUB is the default choice for 1824 a slab allocator. 1825 1826config SLOB 1827 depends on EXPERT 1828 bool "SLOB (Simple Allocator)" 1829 help 1830 SLOB replaces the stock allocator with a drastically simpler 1831 allocator. SLOB is generally more space efficient but 1832 does not perform as well on large systems. 1833 1834endchoice 1835 1836config SLAB_FREELIST_RANDOM 1837 default n 1838 depends on SLAB || SLUB 1839 bool "SLAB freelist randomization" 1840 help 1841 Randomizes the freelist order used on creating new pages. This 1842 security feature reduces the predictability of the kernel slab 1843 allocator against heap overflows. 1844 1845config SLUB_CPU_PARTIAL 1846 default y 1847 depends on SLUB && SMP 1848 bool "SLUB per cpu partial cache" 1849 help 1850 Per cpu partial caches accellerate objects allocation and freeing 1851 that is local to a processor at the price of more indeterminism 1852 in the latency of the free. On overflow these caches will be cleared 1853 which requires the taking of locks that may cause latency spikes. 1854 Typically one would choose no for a realtime system. 1855 1856config MMAP_ALLOW_UNINITIALIZED 1857 bool "Allow mmapped anonymous memory to be uninitialized" 1858 depends on EXPERT && !MMU 1859 default n 1860 help 1861 Normally, and according to the Linux spec, anonymous memory obtained 1862 from mmap() has it's contents cleared before it is passed to 1863 userspace. Enabling this config option allows you to request that 1864 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus 1865 providing a huge performance boost. If this option is not enabled, 1866 then the flag will be ignored. 1867 1868 This is taken advantage of by uClibc's malloc(), and also by 1869 ELF-FDPIC binfmt's brk and stack allocator. 1870 1871 Because of the obvious security issues, this option should only be 1872 enabled on embedded devices where you control what is run in 1873 userspace. Since that isn't generally a problem on no-MMU systems, 1874 it is normally safe to say Y here. 1875 1876 See Documentation/nommu-mmap.txt for more information. 1877 1878config SYSTEM_DATA_VERIFICATION 1879 def_bool n 1880 select SYSTEM_TRUSTED_KEYRING 1881 select KEYS 1882 select CRYPTO 1883 select CRYPTO_RSA 1884 select ASYMMETRIC_KEY_TYPE 1885 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE 1886 select ASN1 1887 select OID_REGISTRY 1888 select X509_CERTIFICATE_PARSER 1889 select PKCS7_MESSAGE_PARSER 1890 help 1891 Provide PKCS#7 message verification using the contents of the system 1892 trusted keyring to provide public keys. This then can be used for 1893 module verification, kexec image verification and firmware blob 1894 verification. 1895 1896config PROFILING 1897 bool "Profiling support" 1898 help 1899 Say Y here to enable the extended profiling support mechanisms used 1900 by profilers such as OProfile. 1901 1902# 1903# Place an empty function call at each tracepoint site. Can be 1904# dynamically changed for a probe function. 1905# 1906config TRACEPOINTS 1907 bool 1908 1909source "arch/Kconfig" 1910 1911endmenu # General setup 1912 1913config HAVE_GENERIC_DMA_COHERENT 1914 bool 1915 default n 1916 1917config SLABINFO 1918 bool 1919 depends on PROC_FS 1920 depends on SLAB || SLUB_DEBUG 1921 default y 1922 1923config RT_MUTEXES 1924 bool 1925 1926config BASE_SMALL 1927 int 1928 default 0 if BASE_FULL 1929 default 1 if !BASE_FULL 1930 1931menuconfig MODULES 1932 bool "Enable loadable module support" 1933 option modules 1934 help 1935 Kernel modules are small pieces of compiled code which can 1936 be inserted in the running kernel, rather than being 1937 permanently built into the kernel. You use the "modprobe" 1938 tool to add (and sometimes remove) them. If you say Y here, 1939 many parts of the kernel can be built as modules (by 1940 answering M instead of Y where indicated): this is most 1941 useful for infrequently used options which are not required 1942 for booting. For more information, see the man pages for 1943 modprobe, lsmod, modinfo, insmod and rmmod. 1944 1945 If you say Y here, you will need to run "make 1946 modules_install" to put the modules under /lib/modules/ 1947 where modprobe can find them (you may need to be root to do 1948 this). 1949 1950 If unsure, say Y. 1951 1952if MODULES 1953 1954config MODULE_FORCE_LOAD 1955 bool "Forced module loading" 1956 default n 1957 help 1958 Allow loading of modules without version information (ie. modprobe 1959 --force). Forced module loading sets the 'F' (forced) taint flag and 1960 is usually a really bad idea. 1961 1962config MODULE_UNLOAD 1963 bool "Module unloading" 1964 help 1965 Without this option you will not be able to unload any 1966 modules (note that some modules may not be unloadable 1967 anyway), which makes your kernel smaller, faster 1968 and simpler. If unsure, say Y. 1969 1970config MODULE_FORCE_UNLOAD 1971 bool "Forced module unloading" 1972 depends on MODULE_UNLOAD 1973 help 1974 This option allows you to force a module to unload, even if the 1975 kernel believes it is unsafe: the kernel will remove the module 1976 without waiting for anyone to stop using it (using the -f option to 1977 rmmod). This is mainly for kernel developers and desperate users. 1978 If unsure, say N. 1979 1980config MODVERSIONS 1981 bool "Module versioning support" 1982 help 1983 Usually, you have to use modules compiled with your kernel. 1984 Saying Y here makes it sometimes possible to use modules 1985 compiled for different kernels, by adding enough information 1986 to the modules to (hopefully) spot any changes which would 1987 make them incompatible with the kernel you are running. If 1988 unsure, say N. 1989 1990config MODULE_SRCVERSION_ALL 1991 bool "Source checksum for all modules" 1992 help 1993 Modules which contain a MODULE_VERSION get an extra "srcversion" 1994 field inserted into their modinfo section, which contains a 1995 sum of the source files which made it. This helps maintainers 1996 see exactly which source was used to build a module (since 1997 others sometimes change the module source without updating 1998 the version). With this option, such a "srcversion" field 1999 will be created for all modules. If unsure, say N. 2000 2001config MODULE_SIG 2002 bool "Module signature verification" 2003 depends on MODULES 2004 select SYSTEM_DATA_VERIFICATION 2005 help 2006 Check modules for valid signatures upon load: the signature 2007 is simply appended to the module. For more information see 2008 Documentation/module-signing.txt. 2009 2010 Note that this option adds the OpenSSL development packages as a 2011 kernel build dependency so that the signing tool can use its crypto 2012 library. 2013 2014 !!!WARNING!!! If you enable this option, you MUST make sure that the 2015 module DOES NOT get stripped after being signed. This includes the 2016 debuginfo strip done by some packagers (such as rpmbuild) and 2017 inclusion into an initramfs that wants the module size reduced. 2018 2019config MODULE_SIG_FORCE 2020 bool "Require modules to be validly signed" 2021 depends on MODULE_SIG 2022 help 2023 Reject unsigned modules or signed modules for which we don't have a 2024 key. Without this, such modules will simply taint the kernel. 2025 2026config MODULE_SIG_ALL 2027 bool "Automatically sign all modules" 2028 default y 2029 depends on MODULE_SIG 2030 help 2031 Sign all modules during make modules_install. Without this option, 2032 modules must be signed manually, using the scripts/sign-file tool. 2033 2034comment "Do not forget to sign required modules with scripts/sign-file" 2035 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL 2036 2037choice 2038 prompt "Which hash algorithm should modules be signed with?" 2039 depends on MODULE_SIG 2040 help 2041 This determines which sort of hashing algorithm will be used during 2042 signature generation. This algorithm _must_ be built into the kernel 2043 directly so that signature verification can take place. It is not 2044 possible to load a signed module containing the algorithm to check 2045 the signature on that module. 2046 2047config MODULE_SIG_SHA1 2048 bool "Sign modules with SHA-1" 2049 select CRYPTO_SHA1 2050 2051config MODULE_SIG_SHA224 2052 bool "Sign modules with SHA-224" 2053 select CRYPTO_SHA256 2054 2055config MODULE_SIG_SHA256 2056 bool "Sign modules with SHA-256" 2057 select CRYPTO_SHA256 2058 2059config MODULE_SIG_SHA384 2060 bool "Sign modules with SHA-384" 2061 select CRYPTO_SHA512 2062 2063config MODULE_SIG_SHA512 2064 bool "Sign modules with SHA-512" 2065 select CRYPTO_SHA512 2066 2067endchoice 2068 2069config MODULE_SIG_HASH 2070 string 2071 depends on MODULE_SIG 2072 default "sha1" if MODULE_SIG_SHA1 2073 default "sha224" if MODULE_SIG_SHA224 2074 default "sha256" if MODULE_SIG_SHA256 2075 default "sha384" if MODULE_SIG_SHA384 2076 default "sha512" if MODULE_SIG_SHA512 2077 2078config MODULE_COMPRESS 2079 bool "Compress modules on installation" 2080 depends on MODULES 2081 help 2082 2083 Compresses kernel modules when 'make modules_install' is run; gzip or 2084 xz depending on "Compression algorithm" below. 2085 2086 module-init-tools MAY support gzip, and kmod MAY support gzip and xz. 2087 2088 Out-of-tree kernel modules installed using Kbuild will also be 2089 compressed upon installation. 2090 2091 Note: for modules inside an initrd or initramfs, it's more efficient 2092 to compress the whole initrd or initramfs instead. 2093 2094 Note: This is fully compatible with signed modules. 2095 2096 If in doubt, say N. 2097 2098choice 2099 prompt "Compression algorithm" 2100 depends on MODULE_COMPRESS 2101 default MODULE_COMPRESS_GZIP 2102 help 2103 This determines which sort of compression will be used during 2104 'make modules_install'. 2105 2106 GZIP (default) and XZ are supported. 2107 2108config MODULE_COMPRESS_GZIP 2109 bool "GZIP" 2110 2111config MODULE_COMPRESS_XZ 2112 bool "XZ" 2113 2114endchoice 2115 2116config TRIM_UNUSED_KSYMS 2117 bool "Trim unused exported kernel symbols" 2118 depends on MODULES && !UNUSED_SYMBOLS 2119 help 2120 The kernel and some modules make many symbols available for 2121 other modules to use via EXPORT_SYMBOL() and variants. Depending 2122 on the set of modules being selected in your kernel configuration, 2123 many of those exported symbols might never be used. 2124 2125 This option allows for unused exported symbols to be dropped from 2126 the build. In turn, this provides the compiler more opportunities 2127 (especially when using LTO) for optimizing the code and reducing 2128 binary size. This might have some security advantages as well. 2129 2130 If unsure, or if you need to build out-of-tree modules, say N. 2131 2132endif # MODULES 2133 2134config MODULES_TREE_LOOKUP 2135 def_bool y 2136 depends on PERF_EVENTS || TRACING 2137 2138config INIT_ALL_POSSIBLE 2139 bool 2140 help 2141 Back when each arch used to define their own cpu_online_mask and 2142 cpu_possible_mask, some of them chose to initialize cpu_possible_mask 2143 with all 1s, and others with all 0s. When they were centralised, 2144 it was better to provide this option than to break all the archs 2145 and have several arch maintainers pursuing me down dark alleys. 2146 2147source "block/Kconfig" 2148 2149config PREEMPT_NOTIFIERS 2150 bool 2151 2152config PADATA 2153 depends on SMP 2154 bool 2155 2156config ASN1 2157 tristate 2158 help 2159 Build a simple ASN.1 grammar compiler that produces a bytecode output 2160 that can be interpreted by the ASN.1 stream decoder and used to 2161 inform it as to what tags are to be expected in a stream and what 2162 functions to call on what tags. 2163 2164source "kernel/Kconfig.locks" 2165