From: Mel Gorman <mgorman@techsingularity.net>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>,
Davidlohr Bueso <dave@stgolabs.net>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH] sched: Fix rq->nr_iowait ordering
Date: Tue, 17 Nov 2020 11:43:18 +0000 [thread overview]
Message-ID: <20201117114318.GX3371@techsingularity.net> (raw)
In-Reply-To: <20201117093829.GD3121429@hirez.programming.kicks-ass.net>
On Tue, Nov 17, 2020 at 10:38:29AM +0100, Peter Zijlstra wrote:
> 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>
s/Fixes: Fixes:/Fixes:/
Ok, very minor hazard that the same logic gets duplicated that someone
might try "fix" but git blame should help. Otherwise, it makes sense as
I've received more than one "bug" that complained that a number was larger
than they expected even if no other problem was present so
Acked-by: Mel Gorman <mgorman@techsingularity.net>
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2020-11-17 11:43 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-16 9:10 Loadavg accounting error on arm64 Mel Gorman
2020-11-16 11:49 ` Mel Gorman
2020-11-16 12:00 ` Mel Gorman
2020-11-16 12:53 ` Peter Zijlstra
2020-11-16 12:58 ` Peter Zijlstra
2020-11-16 15:29 ` Mel Gorman
2020-11-16 16:42 ` Mel Gorman
2020-11-16 16:49 ` Peter Zijlstra
2020-11-16 17:24 ` Mel Gorman
2020-11-16 17:41 ` Will Deacon
2020-11-16 12:46 ` Peter Zijlstra
2020-11-16 12:58 ` Mel Gorman
2020-11-16 13:11 ` Will Deacon
2020-11-16 13:37 ` Mel Gorman
2020-11-16 14:20 ` Peter Zijlstra
2020-11-16 15:52 ` Mel Gorman
2020-11-16 16:54 ` Peter Zijlstra
2020-11-16 17:16 ` Mel Gorman
2020-11-16 19:31 ` Mel Gorman
2020-11-17 8:30 ` [PATCH] sched: Fix data-race in wakeup Peter Zijlstra
2020-11-17 9:15 ` Will Deacon
2020-11-17 9:29 ` Peter Zijlstra
2020-11-17 9:46 ` Peter Zijlstra
2020-11-17 10:36 ` Will Deacon
2020-11-17 12:52 ` Valentin Schneider
2020-11-17 15:37 ` Valentin Schneider
2020-11-17 16:13 ` Peter Zijlstra
2020-11-17 19:32 ` Valentin Schneider
2020-11-18 8:05 ` Peter Zijlstra
2020-11-18 9:51 ` Valentin Schneider
2020-11-18 13:33 ` Marco Elver
2020-11-17 9:38 ` [PATCH] sched: Fix rq->nr_iowait ordering Peter Zijlstra
2020-11-17 11:43 ` Mel Gorman [this message]
2020-11-19 9:55 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2020-11-17 12:40 ` [PATCH] sched: Fix data-race in wakeup Mel Gorman
2020-11-19 9:55 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
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