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From: Tejun Heo <tj@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, Rik van Riel <riel@surriel.com>
Subject: sched: rq->nr_iowait transiently going negative after the recent p->on_cpu optimization
Date: Fri, 18 Sep 2020 13:27:59 -0400	[thread overview]
Message-ID: <20200918172759.GA4247@mtj.thefacebook.com> (raw)

Hello,

Peter, I noticed /proc/stat::procs_blocked going U64_MAX transiently once in
the blue moon without any other persistent issues. After looking at the code
with Rik for a bit, the culprit seems to be c6e7bd7afaeb ("sched/core:
Optimize ttwu() spinning on p->on_cpu") - it changed where ttwu dec's
nr_iowait and it looks like that can happen before the target task gets to
inc.

Thanks.

-- 
tejun

             reply	other threads:[~2020-09-18 17:28 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-18 17:27 Tejun Heo [this message]
2020-09-24 11:50 ` sched: rq->nr_iowait transiently going negative after the recent p->on_cpu optimization Peter Zijlstra
2020-09-24 14:27   ` Tejun Heo
2020-09-24 14:50     ` Peter Zijlstra
2020-09-24 14:57       ` Tejun Heo

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