From 4892f51ad54ddff2883a60b6ad4323c1f632a9d6 Mon Sep 17 00:00:00 2001 From: Quentin Perret Date: Fri, 20 Sep 2019 11:41:15 +0200 Subject: [PATCH] sched/fair: Avoid redundant EAS calculation The EAS wake-up path computes the system energy for several CPU candidates: the CPU with maximum spare capacity in each performance domain, and the prev_cpu. However, if prev_cpu also happens to be the CPU with maximum spare capacity in its performance domain, the energy calculation is still done twice, unnecessarily. Add a condition to filter out this corner case before doing the energy calculation. Reported-by: Pavan Kondeti Signed-off-by: Quentin Perret Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: dietmar.eggemann@arm.com Cc: juri.lelli@redhat.com Cc: morten.rasmussen@arm.com Cc: qais.yousef@arm.com Cc: rjw@rjwysocki.net Cc: tkjos@google.com Cc: valentin.schneider@arm.com Cc: vincent.guittot@linaro.org Fixes: eb92692b2544 ("sched/fair: Speed-up energy-aware wake-ups") Link: https://lkml.kernel.org/r/20190920094115.GA11503@qperret.net Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index dfdac90..83ab35e 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6389,7 +6389,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu) } /* Evaluate the energy impact of using this CPU. */ - if (max_spare_cap_cpu >= 0) { + if (max_spare_cap_cpu >= 0 && max_spare_cap_cpu != prev_cpu) { cur_delta = compute_energy(p, max_spare_cap_cpu, pd); cur_delta -= base_energy_pd; if (cur_delta < best_delta) { -- 2.7.4