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