linux/kernel/sched/features.h

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License cleanup: add SPDX GPL-2.0 license identifier to files with no license Many source files in the tree are missing licensing information, which makes it harder for compliance tools to determine the correct license. By default all files without license information are under the default license of the kernel, which is GPL version 2. Update the files which contain no license information with the 'GPL-2.0' SPDX license identifier. The SPDX identifier is a legally binding shorthand, which can be used instead of the full boiler plate text. This patch is based on work done by Thomas Gleixner and Kate Stewart and Philippe Ombredanne. How this work was done: Patches were generated and checked against linux-4.14-rc6 for a subset of the use cases: - file had no licensing information it it. - file was a */uapi/* one with no licensing information in it, - file was a */uapi/* one with existing licensing information, Further patches will be generated in subsequent months to fix up cases where non-standard license headers were used, and references to license had to be inferred by heuristics based on keywords. The analysis to determine which SPDX License Identifier to be applied to a file was done in a spreadsheet of side by side results from of the output of two independent scanners (ScanCode & Windriver) producing SPDX tag:value files created by Philippe Ombredanne. Philippe prepared the base worksheet, and did an initial spot review of a few 1000 files. The 4.13 kernel was the starting point of the analysis with 60,537 files assessed. Kate Stewart did a file by file comparison of the scanner results in the spreadsheet to determine which SPDX license identifier(s) to be applied to the file. She confirmed any determination that was not immediately clear with lawyers working with the Linux Foundation. Criteria used to select files for SPDX license identifier tagging was: - Files considered eligible had to be source code files. - Make and config files were included as candidates if they contained >5 lines of source - File already had some variant of a license header in it (even if <5 lines). All documentation files were explicitly excluded. The following heuristics were used to determine which SPDX license identifiers to apply. - when both scanners couldn't find any license traces, file was considered to have no license information in it, and the top level COPYING file license applied. For non */uapi/* files that summary was: SPDX license identifier # files ---------------------------------------------------|------- GPL-2.0 11139 and resulted in the first patch in this series. If that file was a */uapi/* path one, it was "GPL-2.0 WITH Linux-syscall-note" otherwise it was "GPL-2.0". Results of that was: SPDX license identifier # files ---------------------------------------------------|------- GPL-2.0 WITH Linux-syscall-note 930 and resulted in the second patch in this series. - if a file had some form of licensing information in it, and was one of the */uapi/* ones, it was denoted with the Linux-syscall-note if any GPL family license was found in the file or had no licensing in it (per prior point). Results summary: SPDX license identifier # files ---------------------------------------------------|------ GPL-2.0 WITH Linux-syscall-note 270 GPL-2.0+ WITH Linux-syscall-note 169 ((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause) 21 ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) 17 LGPL-2.1+ WITH Linux-syscall-note 15 GPL-1.0+ WITH Linux-syscall-note 14 ((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause) 5 LGPL-2.0+ WITH Linux-syscall-note 4 LGPL-2.1 WITH Linux-syscall-note 3 ((GPL-2.0 WITH Linux-syscall-note) OR MIT) 3 ((GPL-2.0 WITH Linux-syscall-note) AND MIT) 1 and that resulted in the third patch in this series. - when the two scanners agreed on the detected license(s), that became the concluded license(s). - when there was disagreement between the two scanners (one detected a license but the other didn't, or they both detected different licenses) a manual inspection of the file occurred. - In most cases a manual inspection of the information in the file resulted in a clear resolution of the license that should apply (and which scanner probably needed to revisit its heuristics). - When it was not immediately clear, the license identifier was confirmed with lawyers working with the Linux Foundation. - If there was any question as to the appropriate license identifier, the file was flagged for further research and to be revisited later in time. In total, over 70 hours of logged manual review was done on the spreadsheet to determine the SPDX license identifiers to apply to the source files by Kate, Philippe, Thomas and, in some cases, confirmation by lawyers working with the Linux Foundation. Kate also obtained a third independent scan of the 4.13 code base from FOSSology, and compared selected files where the other two scanners disagreed against that SPDX file, to see if there was new insights. The Windriver scanner is based on an older version of FOSSology in part, so they are related. Thomas did random spot checks in about 500 files from the spreadsheets for the uapi headers and agreed with SPDX license identifier in the files he inspected. For the non-uapi files Thomas did random spot checks in about 15000 files. In initial set of patches against 4.14-rc6, 3 files were found to have copy/paste license identifier errors, and have been fixed to reflect the correct identifier. Additionally Philippe spent 10 hours this week doing a detailed manual inspection and review of the 12,461 patched files from the initial patch version early this week with: - a full scancode scan run, collecting the matched texts, detected license ids and scores - reviewing anything where there was a license detected (about 500+ files) to ensure that the applied SPDX license was correct - reviewing anything where there was no detection but the patch license was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied SPDX license was correct This produced a worksheet with 20 files needing minor correction. This worksheet was then exported into 3 different .csv files for the different types of files to be modified. These .csv files were then reviewed by Greg. Thomas wrote a script to parse the csv files and add the proper SPDX tag to the file, in the format that the file expected. This script was further refined by Greg based on the output to detect more types of files automatically and to distinguish between header and source .c files (which need different comment types.) Finally Greg ran the script using the .csv files to generate the patches. Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org> Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2017-11-01 15:07:57 +01:00
/* SPDX-License-Identifier: GPL-2.0 */
/*
* Only give sleepers 50% of their service deficit. This allows
* them to run sooner, but does not allow tons of sleepers to
* rip the spread apart.
*/
SCHED_FEAT(GENTLE_FAIR_SLEEPERS, true)
/*
* Place new tasks ahead so that they do not starve already running
* tasks
*/
SCHED_FEAT(START_DEBIT, true)
/*
* Prefer to schedule the task we woke last (assuming it failed
* wakeup-preemption), since its likely going to consume data we
* touched, increases cache locality.
*/
SCHED_FEAT(NEXT_BUDDY, false)
/*
* Prefer to schedule the task that ran last (when we did
* wake-preempt) as that likely will touch the same data, increases
* cache locality.
*/
SCHED_FEAT(LAST_BUDDY, true)
/*
* Consider buddies to be cache hot, decreases the likelyness of a
* cache buddy being migrated away, increases cache locality.
*/
SCHED_FEAT(CACHE_HOT_BUDDY, true)
/*
* Allow wakeup-time preemption of the current task:
*/
SCHED_FEAT(WAKEUP_PREEMPTION, true)
SCHED_FEAT(HRTICK, false)
SCHED_FEAT(DOUBLE_TICK, false)
sched/fair: Disable LB_BIAS by default LB_BIAS allows the adjustment on how conservative load should be balanced. The rq->cpu_load[idx] array is used for this functionality. It contains weighted CPU load decayed average values over different intervals (idx = 1..4). Idx = 0 is the weighted CPU load itself. The values are updated during scheduler_tick, before idle balance and at nohz exit. There are 5 different types of idx's per sched domain (sd). Each of them is used to index into the rq->cpu_load[idx] array in a specific scenario (busy, idle and newidle for load balancing, forkexec for wake-up slow-path load balancing and wake for affine wakeup based on weight). Only the sd idx's for busy and idle load balancing are set to 2,3 or 1,2 respectively. All the other sd idx's are set to 0. Conservative load balancing is achieved for sd idx's >= 1 by using the min/max (source_load()/target_load()) value between the current weighted CPU load and the rq->cpu_load[sd idx -1] for the busiest(idlest)/local CPU load in load balancing or vice versa in the wake-up slow-path load balancing. There is no conservative balancing for sd idx = 0 since only current weighted CPU load is used in this case. It is very likely that LB_BIAS' influence on load balancing can be neglected (see test results below). This is further supported by: (1) Weighted CPU load today is by itself a decayed average value (PELT) (cfs_rq->avg->runnable_load_avg) and not the instantaneous load (rq->load.weight) it was when LB_BIAS was introduced. (2) Sd imbalance_pct is used for CPU_NEWLY_IDLE and CPU_NOT_IDLE (relate to sd's newidle and busy idx) in find_busiest_group() when comparing busiest and local avg load to make load balancing even more conservative. (3) The sd forkexec and newidle idx are always set to 0 so there is no adjustment on how conservatively load balancing is done here. (4) Affine wakeup based on weight (wake_affine_weight()) will not be impacted since the sd wake idx is always set to 0. Let's disable LB_BIAS by default for a few kernel releases to make sure that no workload and no scheduler topology is affected. The benefit of being able to remove the LB_BIAS dependency from source_load() and target_load() is that the entire rq->cpu_load[idx] code could be removed in this case. It is really hard to say if there is no regression w/o testing this with a lot of different workloads on a lot of different platforms, especially NUMA machines. The following 104 LKP (Linux Kernel Performance) tests were run by the 0-Day guys mostly on multi-socket hosts with a larger number of logical cpus (88, 192). The base for the test was commit b3dae109fa89 ("sched/swait: Rename to exclusive") (tip/sched/core v4.18-rc1). Only 2 out of the 104 tests had a significant change in one of the metrics (fsmark/1x-1t-1HDD-btrfs-nfsv4-4M-60G-NoSync-performance +7% files_per_sec, unixbench/300s-100%-syscall-performance -11% score). Tests which showed a change in one of the metrics are marked with a '*' and this change is listed as well. (a) lkp-bdw-ep3: 88 threads Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz 64G dd-write/10m-1HDD-cfq-btrfs-100dd-performance fsmark/1x-1t-1HDD-xfs-nfsv4-4M-60G-NoSync-performance * fsmark/1x-1t-1HDD-btrfs-nfsv4-4M-60G-NoSync-performance 7.50 7% 8.00 ± 6% fsmark.files_per_sec fsmark/1x-1t-1HDD-btrfs-nfsv4-4M-60G-fsyncBeforeClose-performance fsmark/1x-1t-1HDD-btrfs-4M-60G-NoSync-performance fsmark/1x-1t-1HDD-btrfs-4M-60G-fsyncBeforeClose-performance kbuild/300s-50%-vmlinux_prereq-performance kbuild/300s-200%-vmlinux_prereq-performance kbuild/300s-50%-vmlinux_prereq-performance-1HDD-ext4 kbuild/300s-200%-vmlinux_prereq-performance-1HDD-ext4 (b) lkp-skl-4sp1: 192 threads Intel(R) Xeon(R) Platinum 8160 768G dbench/100%-performance ebizzy/200%-100x-10s-performance hackbench/1600%-process-pipe-performance iperf/300s-cs-localhost-tcp-performance iperf/300s-cs-localhost-udp-performance perf-bench-numa-mem/2t-300M-performance perf-bench-sched-pipe/10000000ops-process-performance perf-bench-sched-pipe/10000000ops-threads-performance schbench/2-16-300-30000-30000-performance tbench/100%-cs-localhost-performance (c) lkp-bdw-ep6: 88 threads Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz 128G stress-ng/100%-60s-pipe-performance unixbench/300s-1-whetstone-double-performance unixbench/300s-1-shell1-performance unixbench/300s-1-shell8-performance unixbench/300s-1-pipe-performance * unixbench/300s-1-context1-performance 312 315 unixbench.score unixbench/300s-1-spawn-performance unixbench/300s-1-syscall-performance unixbench/300s-1-dhry2reg-performance unixbench/300s-1-fstime-performance unixbench/300s-1-fsbuffer-performance unixbench/300s-1-fsdisk-performance unixbench/300s-100%-whetstone-double-performance unixbench/300s-100%-shell1-performance unixbench/300s-100%-shell8-performance unixbench/300s-100%-pipe-performance unixbench/300s-100%-context1-performance unixbench/300s-100%-spawn-performance * unixbench/300s-100%-syscall-performance 3571 ± 3% -11% 3183 ± 4% unixbench.score unixbench/300s-100%-dhry2reg-performance unixbench/300s-100%-fstime-performance unixbench/300s-100%-fsbuffer-performance unixbench/300s-100%-fsdisk-performance unixbench/300s-1-execl-performance unixbench/300s-100%-execl-performance * will-it-scale/brk1-performance 365004 360387 will-it-scale.per_thread_ops * will-it-scale/dup1-performance 432401 437596 will-it-scale.per_thread_ops will-it-scale/eventfd1-performance will-it-scale/futex1-performance will-it-scale/futex2-performance will-it-scale/futex3-performance will-it-scale/futex4-performance will-it-scale/getppid1-performance will-it-scale/lock1-performance will-it-scale/lseek1-performance will-it-scale/lseek2-performance * will-it-scale/malloc1-performance 47025 45817 will-it-scale.per_thread_ops 77499 76529 will-it-scale.per_process_ops will-it-scale/malloc2-performance * will-it-scale/mmap1-performance 123399 120815 will-it-scale.per_thread_ops 152219 149833 will-it-scale.per_process_ops * will-it-scale/mmap2-performance 107327 104714 will-it-scale.per_thread_ops 136405 133765 will-it-scale.per_process_ops will-it-scale/open1-performance * will-it-scale/open2-performance 171570 168805 will-it-scale.per_thread_ops 532644 526202 will-it-scale.per_process_ops will-it-scale/page_fault1-performance will-it-scale/page_fault2-performance will-it-scale/page_fault3-performance will-it-scale/pipe1-performance will-it-scale/poll1-performance * will-it-scale/poll2-performance 176134 172848 will-it-scale.per_thread_ops 281361 275053 will-it-scale.per_process_ops will-it-scale/posix_semaphore1-performance will-it-scale/pread1-performance will-it-scale/pread2-performance will-it-scale/pread3-performance will-it-scale/pthread_mutex1-performance will-it-scale/pthread_mutex2-performance will-it-scale/pwrite1-performance will-it-scale/pwrite2-performance will-it-scale/pwrite3-performance * will-it-scale/read1-performance 1190563 1174833 will-it-scale.per_thread_ops * will-it-scale/read2-performance 1105369 1080427 will-it-scale.per_thread_ops will-it-scale/readseek1-performance * will-it-scale/readseek2-performance 261818 259040 will-it-scale.per_thread_ops will-it-scale/readseek3-performance * will-it-scale/sched_yield-performance 2408059 2382034 will-it-scale.per_thread_ops will-it-scale/signal1-performance will-it-scale/unix1-performance will-it-scale/unlink1-performance will-it-scale/unlink2-performance * will-it-scale/write1-performance 976701 961588 will-it-scale.per_thread_ops * will-it-scale/writeseek1-performance 831898 822448 will-it-scale.per_thread_ops * will-it-scale/writeseek2-performance 228248 225065 will-it-scale.per_thread_ops * will-it-scale/writeseek3-performance 226670 224058 will-it-scale.per_thread_ops will-it-scale/context_switch1-performance aim7/performance-fork_test-2000 * aim7/performance-brk_test-3000 74869 76676 aim7.jobs-per-min aim7/performance-disk_cp-3000 aim7/performance-disk_rd-3000 aim7/performance-sieve-3000 aim7/performance-page_test-3000 aim7/performance-creat-clo-3000 aim7/performance-mem_rtns_1-8000 aim7/performance-disk_wrt-8000 aim7/performance-pipe_cpy-8000 aim7/performance-ram_copy-8000 (d) lkp-avoton3: 8 threads Intel(R) Atom(TM) CPU C2750 @ 2.40GHz 16G netperf/ipv4-900s-200%-cs-localhost-TCP_STREAM-performance Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Fengguang Wu <fengguang.wu@intel.com> Cc: Li Zhijian <zhijianx.li@intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/20180809135753.21077-1-dietmar.eggemann@arm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-08-09 15:57:53 +02:00
SCHED_FEAT(LB_BIAS, false)
/*
sched: Rename capacity related flags It is better not to think about compute capacity as being equivalent to "CPU power". The upcoming "power aware" scheduler work may create confusion with the notion of energy consumption if "power" is used too liberally. Let's rename the following feature flags since they do relate to capacity: SD_SHARE_CPUPOWER -> SD_SHARE_CPUCAPACITY ARCH_POWER -> ARCH_CAPACITY NONTASK_POWER -> NONTASK_CAPACITY Signed-off-by: Nicolas Pitre <nico@linaro.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: Daniel Lezcano <daniel.lezcano@linaro.org> Cc: Morten Rasmussen <morten.rasmussen@arm.com> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net> Cc: linaro-kernel@lists.linaro.org Cc: Andy Fleming <afleming@freescale.com> Cc: Anton Blanchard <anton@samba.org> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Grant Likely <grant.likely@linaro.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Paul Mackerras <paulus@samba.org> Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com> Cc: Rob Herring <robh+dt@kernel.org> Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Cc: Toshi Kani <toshi.kani@hp.com> Cc: Vasant Hegde <hegdevasant@linux.vnet.ibm.com> Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: devicetree@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org Link: http://lkml.kernel.org/n/tip-e93lpnxb87owfievqatey6b5@git.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2014-05-27 19:50:41 +02:00
* Decrement CPU capacity based on time not spent running tasks
*/
sched: Rename capacity related flags It is better not to think about compute capacity as being equivalent to "CPU power". The upcoming "power aware" scheduler work may create confusion with the notion of energy consumption if "power" is used too liberally. Let's rename the following feature flags since they do relate to capacity: SD_SHARE_CPUPOWER -> SD_SHARE_CPUCAPACITY ARCH_POWER -> ARCH_CAPACITY NONTASK_POWER -> NONTASK_CAPACITY Signed-off-by: Nicolas Pitre <nico@linaro.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: Daniel Lezcano <daniel.lezcano@linaro.org> Cc: Morten Rasmussen <morten.rasmussen@arm.com> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net> Cc: linaro-kernel@lists.linaro.org Cc: Andy Fleming <afleming@freescale.com> Cc: Anton Blanchard <anton@samba.org> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Grant Likely <grant.likely@linaro.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Paul Mackerras <paulus@samba.org> Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com> Cc: Rob Herring <robh+dt@kernel.org> Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Cc: Toshi Kani <toshi.kani@hp.com> Cc: Vasant Hegde <hegdevasant@linux.vnet.ibm.com> Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: devicetree@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org Link: http://lkml.kernel.org/n/tip-e93lpnxb87owfievqatey6b5@git.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2014-05-27 19:50:41 +02:00
SCHED_FEAT(NONTASK_CAPACITY, true)
/*
* Queue remote wakeups on the target CPU and process them
* using the scheduler IPI. Reduces rq->lock contention/bounces.
*/
SCHED_FEAT(TTWU_QUEUE, true)
/*
* When doing wakeups, attempt to limit superfluous scans of the LLC domain.
*/
SCHED_FEAT(SIS_AVG_CPU, false)
sched/core: Implement new approach to scale select_idle_cpu() Hackbench recently suffered a bunch of pain, first by commit: 4c77b18cf8b7 ("sched/fair: Make select_idle_cpu() more aggressive") and then by commit: c743f0a5c50f ("sched/fair, cpumask: Export for_each_cpu_wrap()") which fixed a bug in the initial for_each_cpu_wrap() implementation that made select_idle_cpu() even more expensive. The bug was that it would skip over CPUs when bits were consequtive in the bitmask. This however gave me an idea to fix select_idle_cpu(); where the old scheme was a cliff-edge throttle on idle scanning, this introduces a more gradual approach. Instead of stopping to scan entirely, we limit how many CPUs we scan. Initial benchmarks show that it mostly recovers hackbench while not hurting anything else, except Mason's schbench, but not as bad as the old thing. It also appears to recover the tbench high-end, which also suffered like hackbench. Tested-by: Matt Fleming <matt@codeblueprint.co.uk> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Chris Mason <clm@fb.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: hpa@zytor.com Cc: kitsunyan <kitsunyan@inbox.ru> Cc: linux-kernel@vger.kernel.org Cc: lvenanci@redhat.com Cc: riel@redhat.com Cc: xiaolong.ye@intel.com Link: http://lkml.kernel.org/r/20170517105350.hk5m4h4jb6dfr65a@hirez.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-05-17 12:53:50 +02:00
SCHED_FEAT(SIS_PROP, true)
/*
* Issue a WARN when we do multiple update_rq_clock() calls
* in a single rq->lock section. Default disabled because the
* annotations are not complete.
*/
SCHED_FEAT(WARN_DOUBLE_CLOCK, false)
sched/rt: Use IPI to trigger RT task push migration instead of pulling When debugging the latencies on a 40 core box, where we hit 300 to 500 microsecond latencies, I found there was a huge contention on the runqueue locks. Investigating it further, running ftrace, I found that it was due to the pulling of RT tasks. The test that was run was the following: cyclictest --numa -p95 -m -d0 -i100 This created a thread on each CPU, that would set its wakeup in iterations of 100 microseconds. The -d0 means that all the threads had the same interval (100us). Each thread sleeps for 100us and wakes up and measures its latencies. cyclictest is maintained at: git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git What happened was another RT task would be scheduled on one of the CPUs that was running our test, when the other CPU tests went to sleep and scheduled idle. This caused the "pull" operation to execute on all these CPUs. Each one of these saw the RT task that was overloaded on the CPU of the test that was still running, and each one tried to grab that task in a thundering herd way. To grab the task, each thread would do a double rq lock grab, grabbing its own lock as well as the rq of the overloaded CPU. As the sched domains on this box was rather flat for its size, I saw up to 12 CPUs block on this lock at once. This caused a ripple affect with the rq locks especially since the taking was done via a double rq lock, which means that several of the CPUs had their own rq locks held while trying to take this rq lock. As these locks were blocked, any wakeups or load balanceing on these CPUs would also block on these locks, and the wait time escalated. I've tried various methods to lessen the load, but things like an atomic counter to only let one CPU grab the task wont work, because the task may have a limited affinity, and we may pick the wrong CPU to take that lock and do the pull, to only find out that the CPU we picked isn't in the task's affinity. Instead of doing the PULL, I now have the CPUs that want the pull to send over an IPI to the overloaded CPU, and let that CPU pick what CPU to push the task to. No more need to grab the rq lock, and the push/pull algorithm still works fine. With this patch, the latency dropped to just 150us over a 20 hour run. Without the patch, the huge latencies would trigger in seconds. I've created a new sched feature called RT_PUSH_IPI, which is enabled by default. When RT_PUSH_IPI is not enabled, the old method of grabbing the rq locks and having the pulling CPU do the work is implemented. When RT_PUSH_IPI is enabled, the IPI is sent to the overloaded CPU to do a push. To enabled or disable this at run time: # mount -t debugfs nodev /sys/kernel/debug # echo RT_PUSH_IPI > /sys/kernel/debug/sched_features or # echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched_features Update: This original patch would send an IPI to all CPUs in the RT overload list. But that could theoretically cause the reverse issue. That is, there could be lots of overloaded RT queues and one CPU lowers its priority. It would then send an IPI to all the overloaded RT queues and they could then all try to grab the rq lock of the CPU lowering its priority, and then we have the same problem. The latest design sends out only one IPI to the first overloaded CPU. It tries to push any tasks that it can, and then looks for the next overloaded CPU that can push to the source CPU. The IPIs stop when all overloaded CPUs that have pushable tasks that have priorities greater than the source CPU are covered. In case the source CPU lowers its priority again, a flag is set to tell the IPI traversal to restart with the first RT overloaded CPU after the source CPU. Parts-suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Joern Engel <joern@purestorage.com> Cc: Clark Williams <williams@redhat.com> Cc: Mike Galbraith <umgwanakikbuti@gmail.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/20150318144946.2f3cc982@gandalf.local.home Signed-off-by: Ingo Molnar <mingo@kernel.org>
2015-03-18 19:49:46 +01:00
#ifdef HAVE_RT_PUSH_IPI
/*
* In order to avoid a thundering herd attack of CPUs that are
* lowering their priorities at the same time, and there being
* a single CPU that has an RT task that can migrate and is waiting
* to run, where the other CPUs will try to take that CPUs
* rq lock and possibly create a large contention, sending an
* IPI to that CPU and let that CPU push the RT task to where
* it should go may be a better scenario.
*/
SCHED_FEAT(RT_PUSH_IPI, true)
#endif
SCHED_FEAT(RT_RUNTIME_SHARE, true)
SCHED_FEAT(LB_MIN, false)
SCHED_FEAT(ATTACH_AGE_LOAD, true)
sched/core: Fix wake_affine() performance regression Eric reported a sysbench regression against commit: 3fed382b46ba ("sched/numa: Implement NUMA node level wake_affine()") Similarly, Rik was looking at the NAS-lu.C benchmark, which regressed against his v3.10 enterprise kernel. PRE (current tip/master): ivb-ep sysbench: 2: [30 secs] transactions: 64110 (2136.94 per sec.) 5: [30 secs] transactions: 143644 (4787.99 per sec.) 10: [30 secs] transactions: 274298 (9142.93 per sec.) 20: [30 secs] transactions: 418683 (13955.45 per sec.) 40: [30 secs] transactions: 320731 (10690.15 per sec.) 80: [30 secs] transactions: 355096 (11834.28 per sec.) hsw-ex NAS: OMP_PROC_BIND/lu.C.x_threads_144_run_1.log: Time in seconds = 18.01 OMP_PROC_BIND/lu.C.x_threads_144_run_2.log: Time in seconds = 17.89 OMP_PROC_BIND/lu.C.x_threads_144_run_3.log: Time in seconds = 17.93 lu.C.x_threads_144_run_1.log: Time in seconds = 434.68 lu.C.x_threads_144_run_2.log: Time in seconds = 405.36 lu.C.x_threads_144_run_3.log: Time in seconds = 433.83 POST (+patch): ivb-ep sysbench: 2: [30 secs] transactions: 64494 (2149.75 per sec.) 5: [30 secs] transactions: 145114 (4836.99 per sec.) 10: [30 secs] transactions: 278311 (9276.69 per sec.) 20: [30 secs] transactions: 437169 (14571.60 per sec.) 40: [30 secs] transactions: 669837 (22326.73 per sec.) 80: [30 secs] transactions: 631739 (21055.88 per sec.) hsw-ex NAS: lu.C.x_threads_144_run_1.log: Time in seconds = 23.36 lu.C.x_threads_144_run_2.log: Time in seconds = 22.96 lu.C.x_threads_144_run_3.log: Time in seconds = 22.52 This patch takes out all the shiny wake_affine() stuff and goes back to utter basics. Between the two CPUs involved with the wakeup (the CPU doing the wakeup and the CPU we ran on previously) pick the CPU we can run on _now_. This restores much of the regressions against the older kernels, but leaves some ground in the overloaded case. The default-enabled WA_WEIGHT (which will be introduced in the next patch) is an attempt to address the overloaded situation. Reported-by: Eric Farman <farman@linux.vnet.ibm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Matthew Rosato <mjrosato@linux.vnet.ibm.com> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: jinpuwang@gmail.com Cc: vcaputo@pengaru.com Fixes: 3fed382b46ba ("sched/numa: Implement NUMA node level wake_affine()") Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-27 11:35:30 +02:00
SCHED_FEAT(WA_IDLE, true)
sched/core: Address more wake_affine() regressions The trivial wake_affine_idle() implementation is very good for a number of workloads, but it comes apart at the moment there are no idle CPUs left, IOW. the overloaded case. hackbench: NO_WA_WEIGHT WA_WEIGHT hackbench-20 : 7.362717561 seconds 6.450509391 seconds (win) netperf: NO_WA_WEIGHT WA_WEIGHT TCP_SENDFILE-1 : Avg: 54524.6 Avg: 52224.3 TCP_SENDFILE-10 : Avg: 48185.2 Avg: 46504.3 TCP_SENDFILE-20 : Avg: 29031.2 Avg: 28610.3 TCP_SENDFILE-40 : Avg: 9819.72 Avg: 9253.12 TCP_SENDFILE-80 : Avg: 5355.3 Avg: 4687.4 TCP_STREAM-1 : Avg: 41448.3 Avg: 42254 TCP_STREAM-10 : Avg: 24123.2 Avg: 25847.9 TCP_STREAM-20 : Avg: 15834.5 Avg: 18374.4 TCP_STREAM-40 : Avg: 5583.91 Avg: 5599.57 TCP_STREAM-80 : Avg: 2329.66 Avg: 2726.41 TCP_RR-1 : Avg: 80473.5 Avg: 82638.8 TCP_RR-10 : Avg: 72660.5 Avg: 73265.1 TCP_RR-20 : Avg: 52607.1 Avg: 52634.5 TCP_RR-40 : Avg: 57199.2 Avg: 56302.3 TCP_RR-80 : Avg: 25330.3 Avg: 26867.9 UDP_RR-1 : Avg: 108266 Avg: 107844 UDP_RR-10 : Avg: 95480 Avg: 95245.2 UDP_RR-20 : Avg: 68770.8 Avg: 68673.7 UDP_RR-40 : Avg: 76231 Avg: 75419.1 UDP_RR-80 : Avg: 34578.3 Avg: 35639.1 UDP_STREAM-1 : Avg: 64684.3 Avg: 66606 UDP_STREAM-10 : Avg: 52701.2 Avg: 52959.5 UDP_STREAM-20 : Avg: 30376.4 Avg: 29704 UDP_STREAM-40 : Avg: 15685.8 Avg: 15266.5 UDP_STREAM-80 : Avg: 8415.13 Avg: 7388.97 (wins and losses) sysbench: NO_WA_WEIGHT WA_WEIGHT sysbench-mysql-2 : 2135.17 per sec. 2142.51 per sec. sysbench-mysql-5 : 4809.68 per sec. 4800.19 per sec. sysbench-mysql-10 : 9158.59 per sec. 9157.05 per sec. sysbench-mysql-20 : 14570.70 per sec. 14543.55 per sec. sysbench-mysql-40 : 22130.56 per sec. 22184.82 per sec. sysbench-mysql-80 : 20995.56 per sec. 21904.18 per sec. sysbench-psql-2 : 1679.58 per sec. 1705.06 per sec. sysbench-psql-5 : 3797.69 per sec. 3879.93 per sec. sysbench-psql-10 : 7253.22 per sec. 7258.06 per sec. sysbench-psql-20 : 11166.75 per sec. 11220.00 per sec. sysbench-psql-40 : 17277.28 per sec. 17359.78 per sec. sysbench-psql-80 : 17112.44 per sec. 17221.16 per sec. (increase on the top end) tbench: NO_WA_WEIGHT Throughput 685.211 MB/sec 2 clients 2 procs max_latency=0.123 ms Throughput 1596.64 MB/sec 5 clients 5 procs max_latency=0.119 ms Throughput 2985.47 MB/sec 10 clients 10 procs max_latency=0.262 ms Throughput 4521.15 MB/sec 20 clients 20 procs max_latency=0.506 ms Throughput 9438.1 MB/sec 40 clients 40 procs max_latency=2.052 ms Throughput 8210.5 MB/sec 80 clients 80 procs max_latency=8.310 ms WA_WEIGHT Throughput 697.292 MB/sec 2 clients 2 procs max_latency=0.127 ms Throughput 1596.48 MB/sec 5 clients 5 procs max_latency=0.080 ms Throughput 2975.22 MB/sec 10 clients 10 procs max_latency=0.254 ms Throughput 4575.14 MB/sec 20 clients 20 procs max_latency=0.502 ms Throughput 9468.65 MB/sec 40 clients 40 procs max_latency=2.069 ms Throughput 8631.73 MB/sec 80 clients 80 procs max_latency=8.605 ms (increase on the top end) Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Rik van Riel <riel@redhat.com> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-06 09:23:24 +02:00
SCHED_FEAT(WA_WEIGHT, true)
SCHED_FEAT(WA_BIAS, true)
sched/fair: Add util_est on top of PELT The util_avg signal computed by PELT is too variable for some use-cases. For example, a big task waking up after a long sleep period will have its utilization almost completely decayed. This introduces some latency before schedutil will be able to pick the best frequency to run a task. The same issue can affect task placement. Indeed, since the task utilization is already decayed at wakeup, when the task is enqueued in a CPU, this can result in a CPU running a big task as being temporarily represented as being almost empty. This leads to a race condition where other tasks can be potentially allocated on a CPU which just started to run a big task which slept for a relatively long period. Moreover, the PELT utilization of a task can be updated every [ms], thus making it a continuously changing value for certain longer running tasks. This means that the instantaneous PELT utilization of a RUNNING task is not really meaningful to properly support scheduler decisions. For all these reasons, a more stable signal can do a better job of representing the expected/estimated utilization of a task/cfs_rq. Such a signal can be easily created on top of PELT by still using it as an estimator which produces values to be aggregated on meaningful events. This patch adds a simple implementation of util_est, a new signal built on top of PELT's util_avg where: util_est(task) = max(task::util_avg, f(task::util_avg@dequeue)) This allows to remember how big a task has been reported by PELT in its previous activations via f(task::util_avg@dequeue), which is the new _task_util_est(struct task_struct*) function added by this patch. If a task should change its behavior and it runs longer in a new activation, after a certain time its util_est will just track the original PELT signal (i.e. task::util_avg). The estimated utilization of cfs_rq is defined only for root ones. That's because the only sensible consumer of this signal are the scheduler and schedutil when looking for the overall CPU utilization due to FAIR tasks. For this reason, the estimated utilization of a root cfs_rq is simply defined as: util_est(cfs_rq) = max(cfs_rq::util_avg, cfs_rq::util_est::enqueued) where: cfs_rq::util_est::enqueued = sum(_task_util_est(task)) for each RUNNABLE task on that root cfs_rq It's worth noting that the estimated utilization is tracked only for objects of interests, specifically: - Tasks: to better support tasks placement decisions - root cfs_rqs: to better support both tasks placement decisions as well as frequencies selection Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com> Cc: Joel Fernandes <joelaf@google.com> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Morten Rasmussen <morten.rasmussen@arm.com> Cc: Paul Turner <pjt@google.com> Cc: Rafael J . Wysocki <rafael.j.wysocki@intel.com> Cc: Steve Muckle <smuckle@google.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Todd Kjos <tkjos@android.com> Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Link: http://lkml.kernel.org/r/20180309095245.11071-2-patrick.bellasi@arm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-03-09 10:52:42 +01:00
/*
* UtilEstimation. Use estimated CPU utilization.
*/
sched/fair: Update util_est only on util_avg updates The estimated utilization of a task is currently updated every time the task is dequeued. However, to keep overheads under control, PELT signals are effectively updated at maximum once every 1ms. Thus, for really short running tasks, it can happen that their util_avg value has not been updates since their last enqueue. If such tasks are also frequently running tasks (e.g. the kind of workload generated by hackbench) it can also happen that their util_avg is updated only every few activations. This means that updating util_est at every dequeue potentially introduces not necessary overheads and it's also conceptually wrong if the util_avg signal has never been updated during a task activation. Let's introduce a throttling mechanism on task's util_est updates to sync them with util_avg updates. To make the solution memory efficient, both in terms of space and load/store operations, we encode a synchronization flag into the LSB of util_est.enqueued. This makes util_est an even values only metric, which is still considered good enough for its purpose. The synchronization bit is (re)set by __update_load_avg_se() once the PELT signal of a task has been updated during its last activation. Such a throttling mechanism allows to keep under control util_est overheads in the wakeup hot path, thus making it a suitable mechanism which can be enabled also on high-intensity workload systems. Thus, this now switches on by default the estimation utilization scheduler feature. Suggested-by: Chris Redpath <chris.redpath@arm.com> Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> Cc: Joel Fernandes <joelaf@google.com> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Morten Rasmussen <morten.rasmussen@arm.com> Cc: Paul Turner <pjt@google.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rafael J . Wysocki <rafael.j.wysocki@intel.com> Cc: Steve Muckle <smuckle@google.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Todd Kjos <tkjos@android.com> Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Link: http://lkml.kernel.org/r/20180309095245.11071-5-patrick.bellasi@arm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-03-09 10:52:45 +01:00
SCHED_FEAT(UTIL_EST, true)