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63304558ba
Mike and others noticed that EEVDF does like to over-schedule quite a bit -- which does hurt performance of a number of benchmarks / workloads. In particular, what seems to cause over-scheduling is that when lag is of the same order (or larger) than the request / slice then placement will not only cause the task to be placed left of current, but also with a smaller deadline than current, which causes immediate preemption. [ notably, lag bounds are relative to HZ ] Mike suggested we stick to picking 'current' for as long as it's eligible to run, giving it uninterrupted runtime until it reaches parity with the pack. Augment Mike's suggestion by only allowing it to exhaust it's initial request. One random data point: echo NO_RUN_TO_PARITY > /debug/sched/features perf stat -a -e context-switches --repeat 10 -- perf bench sched messaging -g 20 -t -l 5000 3,723,554 context-switches ( +- 0.56% ) 9.5136 +- 0.0394 seconds time elapsed ( +- 0.41% ) echo RUN_TO_PARITY > /debug/sched/features perf stat -a -e context-switches --repeat 10 -- perf bench sched messaging -g 20 -t -l 5000 2,556,535 context-switches ( +- 0.51% ) 9.2427 +- 0.0302 seconds time elapsed ( +- 0.33% ) Suggested-by: Mike Galbraith <umgwanakikbuti@gmail.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20230816134059.GC982867@hirez.programming.kicks-ass.net
91 lines
2.3 KiB
C
91 lines
2.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* Using the avg_vruntime, do the right thing and preserve lag across
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* sleep+wake cycles. EEVDF placement strategy #1, #2 if disabled.
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*/
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SCHED_FEAT(PLACE_LAG, true)
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SCHED_FEAT(PLACE_DEADLINE_INITIAL, true)
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SCHED_FEAT(RUN_TO_PARITY, true)
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/*
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* Prefer to schedule the task we woke last (assuming it failed
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* wakeup-preemption), since its likely going to consume data we
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* touched, increases cache locality.
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*/
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SCHED_FEAT(NEXT_BUDDY, false)
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/*
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* Consider buddies to be cache hot, decreases the likeliness of a
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* cache buddy being migrated away, increases cache locality.
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*/
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SCHED_FEAT(CACHE_HOT_BUDDY, true)
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/*
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* Allow wakeup-time preemption of the current task:
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*/
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SCHED_FEAT(WAKEUP_PREEMPTION, true)
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SCHED_FEAT(HRTICK, false)
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SCHED_FEAT(HRTICK_DL, false)
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SCHED_FEAT(DOUBLE_TICK, false)
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/*
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* Decrement CPU capacity based on time not spent running tasks
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*/
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SCHED_FEAT(NONTASK_CAPACITY, true)
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#ifdef CONFIG_PREEMPT_RT
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SCHED_FEAT(TTWU_QUEUE, false)
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#else
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/*
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* Queue remote wakeups on the target CPU and process them
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* using the scheduler IPI. Reduces rq->lock contention/bounces.
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*/
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SCHED_FEAT(TTWU_QUEUE, true)
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#endif
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/*
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* When doing wakeups, attempt to limit superfluous scans of the LLC domain.
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*/
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SCHED_FEAT(SIS_PROP, false)
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SCHED_FEAT(SIS_UTIL, true)
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/*
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* Issue a WARN when we do multiple update_rq_clock() calls
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* in a single rq->lock section. Default disabled because the
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* annotations are not complete.
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*/
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SCHED_FEAT(WARN_DOUBLE_CLOCK, false)
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#ifdef HAVE_RT_PUSH_IPI
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/*
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* In order to avoid a thundering herd attack of CPUs that are
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* lowering their priorities at the same time, and there being
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* a single CPU that has an RT task that can migrate and is waiting
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* to run, where the other CPUs will try to take that CPUs
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* rq lock and possibly create a large contention, sending an
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* IPI to that CPU and let that CPU push the RT task to where
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* it should go may be a better scenario.
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*/
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SCHED_FEAT(RT_PUSH_IPI, true)
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#endif
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SCHED_FEAT(RT_RUNTIME_SHARE, false)
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SCHED_FEAT(LB_MIN, false)
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SCHED_FEAT(ATTACH_AGE_LOAD, true)
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SCHED_FEAT(WA_IDLE, true)
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SCHED_FEAT(WA_WEIGHT, true)
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SCHED_FEAT(WA_BIAS, true)
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/*
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* UtilEstimation. Use estimated CPU utilization.
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*/
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SCHED_FEAT(UTIL_EST, true)
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SCHED_FEAT(UTIL_EST_FASTUP, true)
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SCHED_FEAT(LATENCY_WARN, false)
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SCHED_FEAT(HZ_BW, true)
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