Messages in this thread Patch in this message | | | Date | Tue, 17 Nov 2020 10:38:29 +0100 | From | Peter Zijlstra <> | Subject | [PATCH] sched: Fix rq->nr_iowait ordering |
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And poking at this reminded me of an order email from TJ that seems to have stagnated.
--- Subject: sched: Fix rq->nr_iowait ordering From: Peter Zijlstra <peterz@infradead.org> Date: Thu, 24 Sep 2020 13:50:42 +0200
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: Fixes: c6e7bd7afaeb ("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> --- kernel/sched/core.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-)
--- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2949,7 +2949,12 @@ ttwu_do_activate(struct rq *rq, struct t #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); @@ -3336,11 +3341,6 @@ try_to_wake_up(struct task_struct *p, un 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 @@ -3411,6 +3411,11 @@ try_to_wake_up(struct task_struct *p, un cpu = select_task_rq(p, p->wake_cpu, wake_flags | WF_TTWU); 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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