linux-kernel - Re: [patch v5 09/15] sched: add power aware scheduling in fork/exec/wake

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Date:	Thu, 21 Feb 2013 14:33:07 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alex Shi <alex.shi@...el.com>
Cc:	torvalds@...ux-foundation.org, mingo@...hat.com,
	tglx@...utronix.de, akpm@...ux-foundation.org,
	arjan@...ux.intel.com, bp@...en8.de, pjt@...gle.com,
	namhyung@...nel.org, efault@....de, vincent.guittot@...aro.org,
	gregkh@...uxfoundation.org, preeti@...ux.vnet.ibm.com,
	viresh.kumar@...aro.org, linux-kernel@...r.kernel.org,
	morten.rasmussen@....com
Subject: Re: [patch v5 09/15] sched: add power aware scheduling in
 fork/exec/wake

On Wed, 2013-02-20 at 22:23 +0800, Alex Shi wrote:
> > But but but,... nr_running is completely unrelated to utilization.
> > 
> 
> Actually, I also hesitated on the name, how about using nr_running to
> replace group_util directly?

The name is a secondary issue, first you need to explain why you think
nr_running is a useful metric at all.

You can have a high nr_running and a low utilization (a burst of
wakeups, each waking a process that'll instantly go to sleep again), or
low nr_running and high utilization (a single process cpu bound
process).

There is absolutely no relation between utilization and nr_running,
building something on that assumption is just wrong and broken.

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