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: <1357597795.5190.10.camel@gandalf.local.home>
Date:	Mon, 07 Jan 2013 17:29:55 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Viresh Kumar <viresh.kumar@...aro.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 Mon, 2013-01-07 at 23:29 +0530, Viresh Kumar wrote:

> > 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.

If you are running on a big.Little box sure. But for normal (read x86 ;)
systems, it should probably stay on the current CPU.

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

Does the caller need to know? Or if you have a big.LITTLE setup, it
should just work automagically?

> 
> 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 :)

Heh, you don't know kernel developers well do you? ;-)

Once a new API is added to the kernel tree, it quickly becomes
(mis)used.

-- Steve


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