linux-kernel - Re: [PATCH V2 Resend 3/4] workqueue: Schedule work on non-idle cpu instead of current one

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Message-ID: <CAKohpom9DxoojtcpMfmyGeUcEw8=tsS4n+TFMRV3+9_UBaod7g@mail.gmail.com>
Date:	Mon, 7 Jan 2013 23:29:53 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Tejun Heo <tj@...nel.org>,
	Vincent Guittot <vincent.guittot@...aro.org>, pjt@...gle.com,
	paul.mckenney@...aro.org, tglx@...utronix.de,
	suresh.b.siddha@...el.com, venki@...gle.com, mingo@...hat.com,
	peterz@...radead.org, Arvind.Chauhan@....com,
	linaro-dev@...ts.linaro.org, patches@...aro.org,
	pdsw-power-team@....com, linux-kernel@...r.kernel.org,
	linux-rt-users@...r.kernel.org
Subject: Re: [PATCH V2 Resend 3/4] workqueue: Schedule work on non-idle cpu
 instead of current one

On 7 January 2013 18:58, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Mon, 2013-01-07 at 15:28 +0530, Viresh Kumar wrote:
>> I have another idea that we can try:
>>
>> queue_work_on_any_cpu().
>
> I think this is a good idea.

:) :)

>> - the mask of cpus to schedule this work on
>>   OR
>> - Sched Level (SD_LEVEL) of cpus to run it.
>
> I wouldn't give a mask. If one is needed, we could have a
> queue_work_on_mask_cpus(), or something. I think the "any" in the name
> should be good enough to let developers know that this will not be on
> the CPU that is called.

Fair Enough.

> By default, I would suggest for cache locality,
> that we try to keep it on the same CPU. But if there's a better CPU to
> run on, it runs there.

That would break our intention behind this routine. We should run
it on a cpu which we think is the best one for it power/performance wise.

So, i would like to call the sched_select_cpu() routine from this routine to
get the suggested cpu.

This routine would however would see more changes later to optimize it
more.

> Also, we could still add a debug option that
> makes it always run on other CPUs to slap developers that don't read.

I don't think we need it :(
It would be a new API, with zero existing users. And so, whomsoever uses
it, should know what exactly he is doing :)

Thanks for your quick feedback.
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