From bec2860a2bd6cd38ea34434d04f4033eb32f0f31 Mon Sep 17 00:00:00 2001 From: Srikar Dronamraju Date: Fri, 6 Dec 2019 22:54:22 +0530 Subject: [PATCH] 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 Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Valentin Schneider Reviewed-by: Vincent Guittot Acked-by: Mel Gorman 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 25dffc03f0f6c..1a0ce83e835a9 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;