From 85dcdaa61b0bc9709d8ac5dc1cfeeab92224112f Mon Sep 17 00:00:00 2001
From: Quentin Perret <qperret@qperret.net>
Date: Fri, 20 Sep 2019 11:41:15 +0200
Subject: [PATCH] sched/fair: Avoid redundant EAS calculation
References: bnc#1155798 (CPU scheduler functional and performance backports)
Patch-mainline: v5.4-rc1
Git-commit: 4892f51ad54ddff2883a60b6ad4323c1f632a9d6
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 <pkondeti@codeaurora.org>
Signed-off-by: Quentin Perret <qperret@qperret.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
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 <mingo@kernel.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
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 e4735347b6e4..21702492939e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6413,7 +6413,7 @@ 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) {