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