Commit 39afe5d6 authored by Libo Chen's avatar Libo Chen Committed by Peter Zijlstra
Browse files

sched/fair: Fix inaccurate tally of ttwu_move_affine 



There are scenarios where non-affine wakeups are incorrectly counted as
affine wakeups by schedstats.

When wake_affine_idle() returns prev_cpu which doesn't equal to
nr_cpumask_bits, it will slip through the check: target == nr_cpumask_bits
in wake_affine() and be counted as if target == this_cpu in schedstats.

Replace target == nr_cpumask_bits with target != this_cpu to make sure
affine wakeups are accurately tallied.

Fixes: 806486c3 (sched/fair: Do not migrate if the prev_cpu is idle)
Suggested-by: default avatarDaniel Jordan <daniel.m.jordan@oracle.com>
Signed-off-by: default avatarLibo Chen <libo.chen@oracle.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarGautham R. Shenoy <gautham.shenoy@amd.com>
Link: https://lore.kernel.org/r/20220810223313.386614-1-libo.chen@oracle.com
parent 05bfb338

kernel/sched/fair.c

+1 −1
Original line number Diff line number Diff line
@@ -6582,7 +6582,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, 
		target = wake_affine_weight(sd, p, this_cpu, prev_cpu, sync);



	schedstat_inc(p->stats.nr_wakeups_affine_attempts);

	if (target == nr_cpumask_bits)

	if (target != this_cpu)

		return prev_cpu;



	schedstat_inc(sd->ttwu_move_affine);