From: Libo Chen libo.chen@oracle.com
[ 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@oracle.com Signed-off-by: Libo Chen libo.chen@oracle.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Gautham R. Shenoy gautham.shenoy@amd.com Link: https://lore.kernel.org/r/20220810223313.386614-1-libo.chen@oracle.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 f70c4a7fb4ef3..fa33c441ae867 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6475,7 +6475,7 @@ 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);