Messages in this thread Patch in this message | | | Date | Wed, 29 Jan 2020 11:32:56 -0000 | From | "tip-bot2 for Srikar Dronamraju" <> | Subject | [tip: sched/core] sched/fair: Optimize select_idle_core() |
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The following commit has been merged into the sched/core branch of tip:
Commit-ID: bec2860a2bd6cd38ea34434d04f4033eb32f0f31 Gitweb: https://git.kernel.org/tip/bec2860a2bd6cd38ea34434d04f4033eb32f0f31 Author: Srikar Dronamraju <srikar@linux.vnet.ibm.com> AuthorDate: Fri, 06 Dec 2019 22:54:22 +05:30 Committer: Ingo Molnar <mingo@kernel.org> CommitterDate: Tue, 28 Jan 2020 21:37:08 +01:00
sched/fair: Optimize select_idle_core()
Currently we loop through all threads of a core to evaluate if the core is idle or not. This is unnecessary. If a thread of a core is not idle, skip evaluating other threads of a core. Also while clearing the cpumask, bits of all CPUs of a core can be cleared in one-shot.
Collecting ticks on a Power 9 SMT 8 system around select_idle_core while running schbench shows us
(units are in ticks, hence lesser is better) Without patch N Min Max Median Avg Stddev x 130 151 1083 284 322.72308 144.41494
With patch N Min Max Median Avg Stddev Improvement x 164 88 610 201 225.79268 106.78943 30.03%
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Reviewed-by: Valentin Schneider <valentin.schneider@arm.com> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org> Acked-by: Mel Gorman <mgorman@techsingularity.net> Link: https://lkml.kernel.org/r/20191206172422.6578-1-srikar@linux.vnet.ibm.com --- kernel/sched/fair.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 25dffc0..1a0ce83 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5787,10 +5787,12 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int bool idle = true; for_each_cpu(cpu, cpu_smt_mask(core)) { - __cpumask_clear_cpu(cpu, cpus); - if (!available_idle_cpu(cpu)) + if (!available_idle_cpu(cpu)) { idle = false; + break; + } } + cpumask_andnot(cpus, cpus, cpu_smt_mask(core)); if (idle) return core;
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