sched: Fix rq->nr_iowait ordering (ec618b84) · Commits · 戴 / test

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() before p->on_cpu==0, we lose the natural ordering and have to further delay the decrement. Fixes: ("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

kernel/sched/core.c

+10 −5

Original line number	Diff line number	Diff line
		@@ -2501,7 +2501,12 @@ ttwu_do_activate(struct rq rq, struct task_struct p, int wake_flags,
		#ifdef CONFIG_SMP
		if (wake_flags & WF_MIGRATED)
		en_flags \|= ENQUEUE_MIGRATED;
		else
		#endif
		if (p->in_iowait) {
		delayacct_blkio_end(p);
		atomic_dec(&task_rq(p)->nr_iowait);
		}

		activate_task(rq, p, en_flags);
		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)
		if (READ_ONCE(p->on_rq) && ttwu_runnable(p, wake_flags))
		goto unlock;

		if (p->in_iowait) {
		delayacct_blkio_end(p);
		atomic_dec(&task_rq(p)->nr_iowait);
		}

		#ifdef CONFIG_SMP
		/*
		* 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)

		cpu = select_task_rq(p, p->wake_cpu, SD_BALANCE_WAKE, wake_flags);
		if (task_cpu(p) != cpu) {
		if (p->in_iowait) {
		delayacct_blkio_end(p);
		atomic_dec(&task_rq(p)->nr_iowait);
		}

		wake_flags \|= WF_MIGRATED;
		psi_ttwu_dequeue(p);
		set_task_cpu(p, cpu);

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