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Commitec618b8

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author
Peter Zijlstra
committed
sched: Fix rq->nr_iowait ordering
 schedule()ttwu() deactivate_task(); if (p->on_rq && ...) // false atomic_dec(&task_rq(p)->nr_iowait); if (prev->in_iowait) atomic_inc(&rq->nr_iowait);Allows nr_iowait to be decremented before it gets incremented,resulting in more dodgy IO-wait numbers than usual.Note that because we can now do ttwu_queue_wakelist() beforep->on_cpu==0, we lose the natural ordering and have to further delaythe decrement.Fixes:c6e7bd7 ("sched/core: Optimize ttwu() spinning on p->on_cpu")Reported-by: Tejun Heo <tj@kernel.org>Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>Acked-by: Mel Gorman <mgorman@techsingularity.net>Link:https://lkml.kernel.org/r/20201117093829.GD3121429@hirez.programming.kicks-ass.net
1 parentf97bb52 commitec618b8

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‎kernel/sched/core.c‎

Lines changed: 10 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -2501,7 +2501,12 @@ ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags,
25012501
#ifdefCONFIG_SMP
25022502
if (wake_flags&WF_MIGRATED)
25032503
en_flags |=ENQUEUE_MIGRATED;
2504+
else
25042505
#endif
2506+
if (p->in_iowait) {
2507+
delayacct_blkio_end(p);
2508+
atomic_dec(&task_rq(p)->nr_iowait);
2509+
}
25052510

25062511
activate_task(rq,p,en_flags);
25072512
ttwu_do_wakeup(rq,p,wake_flags,rf);
@@ -2888,11 +2893,6 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
28882893
if (READ_ONCE(p->on_rq)&&ttwu_runnable(p,wake_flags))
28892894
gotounlock;
28902895

2891-
if (p->in_iowait) {
2892-
delayacct_blkio_end(p);
2893-
atomic_dec(&task_rq(p)->nr_iowait);
2894-
}
2895-
28962896
#ifdefCONFIG_SMP
28972897
/*
28982898
* Ensure we load p->on_cpu _after_ p->on_rq, otherwise it would be
@@ -2963,6 +2963,11 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
29632963

29642964
cpu=select_task_rq(p,p->wake_cpu,SD_BALANCE_WAKE,wake_flags);
29652965
if (task_cpu(p)!=cpu) {
2966+
if (p->in_iowait) {
2967+
delayacct_blkio_end(p);
2968+
atomic_dec(&task_rq(p)->nr_iowait);
2969+
}
2970+
29662971
wake_flags |=WF_MIGRATED;
29672972
psi_ttwu_dequeue(p);
29682973
set_task_cpu(p,cpu);

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