linux-kernel - Re: [patch v7 0/21] sched: power aware scheduling

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Message-ID: <1366989087.30242.11.camel@marge.simpson.net>
Date:	Fri, 26 Apr 2013 17:11:27 +0200
From:	Mike Galbraith <efault@....de>
To:	Len Brown <lenb@...nel.org>
Cc:	Borislav Petkov <bp@...en8.de>, Alex Shi <alex.shi@...el.com>,
	mingo@...hat.com, peterz@...radead.org, tglx@...utronix.de,
	akpm@...ux-foundation.org, arjan@...ux.intel.com, pjt@...gle.com,
	namhyung@...nel.org, morten.rasmussen@....com,
	vincent.guittot@...aro.org, gregkh@...uxfoundation.org,
	preeti@...ux.vnet.ibm.com, viresh.kumar@...aro.org,
	linux-kernel@...r.kernel.org, len.brown@...el.com,
	rafael.j.wysocki@...el.com, jkosina@...e.cz,
	clark.williams@...il.com, tony.luck@...el.com,
	keescook@...omium.org, mgorman@...e.de, riel@...hat.com,
	Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [patch v7 0/21] sched: power aware scheduling

On Wed, 2013-04-17 at 17:53 -0400, Len Brown wrote: 
> On 04/12/2013 12:48 PM, Mike Galbraith wrote:
> > On Fri, 2013-04-12 at 18:23 +0200, Borislav Petkov wrote: 
> >> On Fri, Apr 12, 2013 at 04:46:50PM +0800, Alex Shi wrote:
> >>> Thanks a lot for comments, Len!
> >>
> >> AFAICT, you kinda forgot to answer his most important question:
> >>
> >>> These numbers suggest that this patch series simultaneously
> >>> has a negative impact on performance and energy required
> >>> to retire the workload.  Why do it?
> > 
> > Hm.  When I tested AIM7 compute on a NUMA box, there was a marked
> > throughput increase at the low to moderate load end of the test spectrum
> > IIRC.  Fully repeatable.  There were also other benefits unrelated to
> > power, ie mitigation of the evil face of select_idle_sibling().  I
> > rather liked what I saw during ~big box test-drive.
> > 
> > (just saying there are other aspects besides joules in there)
> 
> Mike,
> 
> Can you re-run your AIM7 measurement with turbo-mode and HT-mode disabled,
> and then independently re-enable them?
> 
> If you still see the performance benefit, then that proves
> that the scheduler hacks are not about tricking into
> turbo mode, but something else.

I did that today, neither turbo nor HT affected the performance gain.  I
used the same box and patch set as tested before (v4), but plugged into
linus HEAD.  "powersaving" AIM7 numbers are ~identical to those I posted
before, "performance" is lower at the low end of AIM7 test spectrum, but
as before, delta goes away once the load becomes hefty.

-Mike

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