Messages in this thread Patch in this message | | | From | Srikar Dronamraju <> | Subject | [PATCH v2] sched/fair: Optimize select_idle_core | Date | Fri, 6 Dec 2019 22:54:22 +0530 |
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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%
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org> Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> --- Changelog v1->v2: Updated patch description with measurements made from a debug patch.
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 69a81a5709ff..b9d628128cfc 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5872,10 +5872,12 @@ 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; -- 2.18.1
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