From: Mel Gorman <mgorman@techsingularity.net>
To: Hillf Danton <hdanton@sina.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Dave Chinner <david@fromorbit.com>,
Ingo Molnar <mingo@redhat.com>, Tejun Heo <tj@kernel.org>,
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: Tue, 28 Jan 2020 13:41:48 +0000 [thread overview]
Message-ID: <20200128134148.GB3466@techsingularity.net> (raw)
In-Reply-To: <20200128130837.11136-1-hdanton@sina.com>
On Tue, Jan 28, 2020 at 09:08:37PM +0800, Hillf Danton wrote:
> > Functionally it works, it's just slow. There is a cost to migration and
> > a cost to exiting from idle state and ramping up the CPU frequency.
> >
> Yeah we need to pay some costs but are not they compensated by the ping
> and pong that waker and wakee are happy to play for ten minutes on
> different cpus sharing cache if you have no way to migrate waker?
>
I could get into it depth but the changelog already mentions the cpufreq
implications and the consequences of round-robining around the machine
as a side-effect of how select_idle_sibling works. The data indicates
that we are not compensated by the migrations.
> Or back to the kworker case, a tradeoff needs to make between making kworker
> able to run on cache-sharing cpus and adding scheduling heuristics. IOW
> is cache affinity the key to the problem?
>
The kworker is already running on CPUs sharing cache. That is not the
central issue.
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2020-01-28 13:41 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200128100643.3016-1-hdanton@sina.com>
2020-01-28 10:32 ` [PATCH] sched, fair: Allow a per-cpu kthread waking a task to stack on the same CPU Mel Gorman
[not found] ` <20200128130837.11136-1-hdanton@sina.com>
2020-01-28 13:41 ` Mel Gorman [this message]
2020-01-27 14:36 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
2020-01-28 14:24 ` Mel Gorman
2020-01-28 22:21 ` Dave Chinner
2020-01-29 10:53 ` Mel Gorman
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