From: Mel Gorman <mgorman@techsingularity.net>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>,
Ingo Molnar <mingo@redhat.com>, Tejun Heo <tj@kernel.org>,
Phil Auld <pauld@redhat.com>, Ming Lei <ming.lei@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] sched, fair: Allow a per-cpu kthread waking a task to stack on the same CPU
Date: Thu, 30 Jan 2020 08:55:13 +0000 [thread overview]
Message-ID: <20200130085513.GH3466@techsingularity.net> (raw)
In-Reply-To: <20200130080653.GV14879@hirez.programming.kicks-ass.net>
On Thu, Jan 30, 2020 at 09:06:53AM +0100, Peter Zijlstra wrote:
> On Thu, Jan 30, 2020 at 12:43:34AM +0000, Mel Gorman wrote:
> > On Wed, Jan 29, 2020 at 06:38:52PM +0100, Peter Zijlstra wrote:
>
> > > I suppose the fact that it limits it to tasks that were running on the
> > > same CPU limits the impact if we do get it wrong.
> > >
> >
> > And it's limited to no other task currently running on the
> > CPU. Now, potentially multiple sleepers are on that CPU waiting for
> > a mutex/rwsem/completion but it's very unlikely and mostly likely due
> > to the machine being saturated in which case searching for an idle CPU
> > will probably fail. It would also be bound by a small window after the
> > first wakeup before the task becomes runnable before the nr_running check
> > mitigages the problem. Besides, if the sleeping task is waiting on the
> > lock, it *is* related to the kworker which is probably finished.
> >
> > In other words, even this patches worst-case behaviour does not seem
> > that bad.
>
> OK; let's just stick it in and see what, if anything, falls over :-)
>
> I saw there is a v2 out (although I didn't see what changed in a hurry),
> let me queue that one.
Only the changelog and comments changed in light of the discussion
with Dave.
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2020-01-30 8:55 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-27 14:36 [PATCH] sched, fair: Allow a per-cpu kthread waking a task to stack on the same CPU Mel Gorman
2020-01-27 22:32 ` Dave Chinner
2020-01-28 1:19 ` Mel Gorman
2020-01-28 9:10 ` Mel Gorman
2020-01-29 17:38 ` Peter Zijlstra
2020-01-29 22:00 ` Dave Chinner
2020-01-30 0:50 ` Mel Gorman
2020-01-30 0:43 ` Mel Gorman
2020-01-30 8:06 ` Peter Zijlstra
2020-01-30 8:55 ` Mel Gorman [this message]
2020-01-28 14:24 ` Mel Gorman
2020-01-28 22:21 ` Dave Chinner
2020-01-29 10:53 ` Mel Gorman
[not found] <20200128100643.3016-1-hdanton@sina.com>
2020-01-28 10:32 ` Mel Gorman
[not found] ` <20200128130837.11136-1-hdanton@sina.com>
2020-01-28 13:41 ` Mel Gorman
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