From: Mel Gorman <mgorman@techsingularity.net>
To: Mike Galbraith <efault@gmx.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/1] RFC: sched/fair: skip select_idle_sibling() in presence of sync wakeups
Date: Wed, 9 Jan 2019 10:07:51 +0000 [thread overview]
Message-ID: <20190109100751.GQ31517@techsingularity.net> (raw)
In-Reply-To: <1547007588.17100.17.camel@gmx.de>
On Wed, Jan 09, 2019 at 05:19:48AM +0100, Mike Galbraith wrote:
> > To test I used this trivial program.
>
> Which highlights the problem. That proggy really is synchronous, but
> the sync hint is applied to many MANY real world cases where this is
> not the case at all. Sure, you can make things like pipe_test and
> nearly nonexistent payload TCP_RR numbers look gorgeous, but that
> demolishes concurrency for real applications.
>
I agree with Mike here. Many previous attempts to strictly obey the strict
hint has led to regressions elsewhere -- specifically a task waking 2+
wakees that temporarily stack on one CPU when nearby CPUs sharing LLC
remain idle. It's why the select idle sibling logic tried to take into
account a recently used CPU to wake such tasks if the recent CPU was
still idle.
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2019-01-09 10:07 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-09 3:49 [PATCH 0/1] RFC: sched/fair: skip select_idle_sibling() in presence of sync wakeups Andrea Arcangeli
2019-01-09 3:49 ` [PATCH 1/1] " Andrea Arcangeli
2019-01-09 4:19 ` [PATCH 0/1] RFC: " Mike Galbraith
2019-01-09 10:07 ` Mel Gorman [this message]
2019-01-09 18:24 ` Andrea Arcangeli
2019-01-09 18:02 ` Andrea Arcangeli
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