From: Andrea Arcangeli <aarcange@redhat.com>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: Mike Galbraith <efault@gmx.de>,
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 13:24:18 -0500 [thread overview]
Message-ID: <20190109182418.GB28624@redhat.com> (raw)
In-Reply-To: <20190109100751.GQ31517@techsingularity.net>
On Wed, Jan 09, 2019 at 10:07:51AM +0000, Mel Gorman wrote:
> 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
sync-waking 2 wakees in a row before going to sleep should cause the
runqueue to have nr_running != 1 after the first wakee is waken up on
the local CPU. Your example explains the following nr_running == 1
check in the patch:
(sync && target == this_cpu && cpu_rq(this_cpu)->nr_running == 1))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The implementation is just an RFC because it may have other drawbacks,
but I thought the second wakee of this specific example supposedly
should still do the idle core/ht balancing normally like before the
change.
Thanks,
Andrea
next prev parent reply other threads:[~2019-01-09 18:24 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
2019-01-09 18:24 ` Andrea Arcangeli [this message]
2019-01-09 18:02 ` Andrea Arcangeli
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