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

From: Mike Galbraith
Date: Fri Apr 26 2013 - 11:11:51 EST

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.


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