From: Quentin Perret <qperret@google.com>
To: Valentin Schneider <valentin.schneider@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Quentin Perret <qperret@qperret.net>,
"open list:SCHEDULER" <linux-kernel@vger.kernel.org>,
kernel-team@android.com, Rick Yiu <rickyiu@google.com>
Subject: Re: [PATCH] sched/fair: Fix overutilized update in enqueue_task_fair()
Date: Thu, 12 Nov 2020 12:38:54 +0000 [thread overview]
Message-ID: <20201112123854.GA2222462@google.com> (raw)
In-Reply-To: <jhjh7puyczc.mognet@arm.com>
On Thursday 12 Nov 2020 at 12:29:59 (+0000), Valentin Schneider wrote:
> Alternatively: how much does not updating the overutilized status here help
> us? The next tick will unconditionally update it, which for arm64 is
> anywhere in the next ]0, 4]ms. That "fake" fork-time util_avg should already
> be accounted in the rq util_avg, and even if the new task was running the
> entire time, 4ms doesn't buy us much decay.
Yes, this is arguably a dodgy hack, which will not save us in a number
of cases. The only situation where this helps is for short-lived tasks
that will run only once. And this is a sadly common programming pattern.
So yeah, this is not the prettiest thing in the world, but it doesn't
cost us much and helps some real-world workloads, so ...
Thanks,
Quentin
next prev parent reply other threads:[~2020-11-12 12:39 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-12 11:12 [PATCH] sched/fair: Fix overutilized update in enqueue_task_fair() Quentin Perret
2020-11-12 12:17 ` Vincent Guittot
2020-11-12 12:29 ` Valentin Schneider
2020-11-12 12:38 ` Quentin Perret [this message]
2020-11-12 12:52 ` Valentin Schneider
2020-11-13 8:18 ` Peter Zijlstra
2020-11-19 9:55 ` [tip: sched/urgent] " tip-bot2 for Quentin Perret
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