[PATCH 6.2 510/663] sched/fair: Fix inaccurate tally of ttwu_move_affine

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From: Libo Chen <libo.chen@xxxxxxxxxx>

[ Upstream commit 39afe5d6fc59237ff7738bf3ede5a8856822d59d ]

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: 806486c377e33 (sched/fair: Do not migrate if the prev_cpu is idle)
Suggested-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Signed-off-by: Libo Chen <libo.chen@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Gautham R. Shenoy <gautham.shenoy@xxxxxxx>
Link: https://lore.kernel.org/r/20220810223313.386614-1-libo.chen@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 661226e38835d..6f1c7a8fa12ab 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6487,7 +6487,7 @@ 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);
-- 
2.39.2






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