From: Mike Galbraith <efault@gmx.de>
To: Peter Zijlstra <peterz@infradead.org>,
Mel Gorman <mgorman@techsingularity.net>
Cc: Ingo Molnar <mingo@redhat.com>,
Matt Fleming <matt@codeblueprint.co.uk>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 3/4] sched: Comment on why sync wakeups try to run on the current CPU
Date: Wed, 20 Dec 2017 05:09:21 +0100 [thread overview]
Message-ID: <1513742961.6863.21.camel@gmx.de> (raw)
In-Reply-To: <20171219190644.3neuaenffj6tcxci@hirez.programming.kicks-ass.net>
On Tue, 2017-12-19 at 20:06 +0100, Peter Zijlstra wrote:
>
> Our SYNC hint does promise the caller will go away 'soon', although I'm
> not sure how many of the current users actually honor that.
The sync hint is not a lie, or even a damn lie, it's a statistic :)
It's very useful for...
TCP_SENDFILE
homer:..debug/tracing # cat trace|grep netperf|grep wakes|wc -l
2417
homer:..debug/tracing # cat trace|grep netperf|grep schedules|wc -l
4
TCP_STREAM
homer:..debug/tracing # cat trace|grep netperf|grep wakes|wc -l
2506
homer:..debug/tracing # cat trace|grep netperf|grep schedules|wc -l
3
TCP_MAERTS
homer:..debug/tracing # cat trace|grep netperf|grep wakes|wc -l
2465
homer:..debug/tracing # cat trace|grep netperf|grep schedules|wc -l
2
...knowing that tasks are talking, but not the least bit useful for
scheduler decisions other than "pull to same planet". Those are single
instances, all of which exceed 180% combined util, one at 100%. Then
there are multi-wakers, tasks that would have scheduled if they hadn't
been given more work to do etc etc. Nope, stacking based upon that
hint is most definitely not a good idea :)
-Mike
next prev parent reply other threads:[~2017-12-20 4:09 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-18 9:43 [PATCH 0/4] Reduce scheduler migrations due to wake_affine Mel Gorman
2017-12-18 9:43 ` [PATCH 1/4] sched: Only immediately migrate tasks due to interrupts if prev and target CPUs share cache Mel Gorman
2017-12-18 9:43 ` [PATCH 2/4] sched: Allow a wakee to run on the prev_cpu if it is idle and cache-affine with the waker Mel Gorman
2017-12-18 10:26 ` Peter Zijlstra
2017-12-18 10:56 ` Mel Gorman
2017-12-18 10:59 ` Peter Zijlstra
2017-12-18 9:43 ` [PATCH 3/4] sched: Comment on why sync wakeups try to run on the current CPU Mel Gorman
2017-12-19 19:06 ` Peter Zijlstra
2017-12-19 20:25 ` Mel Gorman
2017-12-20 4:09 ` Mike Galbraith [this message]
2017-12-20 4:21 ` Mike Galbraith
2017-12-18 9:43 ` [PATCH 4/4] sched: Allow tasks to stack with a workqueue on the same CPU Mel Gorman
2017-12-18 10:44 ` Mike Galbraith
2017-12-18 11:25 ` Mel Gorman
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