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

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Message-ID: <516F19EE.5060309@kernel.org>
Date:	Wed, 17 Apr 2013 17:53:50 -0400
From:	Len Brown <lenb@...nel.org>
To:	Mike Galbraith <efault@....de>
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 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.

If the performance gains *are* about interactions with turbo-mode,
then perhaps what we should really be doing here is making
the scheduler explicitly turbo-aware?  Of course, that begs the question
of how the scheduler should be aware of cpufreq in general...

thanks,
Len Brown, Intel Open Source Technology Center

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