linux-kernel - RE: Performance of low-cpu utilisation benchmark regressed severely since 4.6

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Date:   Fri, 21 Apr 2017 23:29:06 -0700
From:   "Doug Smythies" <dsmythies@...us.net>
To:     "'Rafael J. Wysocki'" <rjw@...ysocki.net>
Cc:     "'Mel Gorman'" <mgorman@...hsingularity.net>,
        "'Rafael Wysocki'" <rafael.j.wysocki@...el.com>,
        'Jörg Otte' <jrg.otte@...il.com>,
        "'Linux Kernel Mailing List'" <linux-kernel@...r.kernel.org>,
        "'Linux PM'" <linux-pm@...r.kernel.org>,
        "'Srinivas Pandruvada'" <srinivas.pandruvada@...ux.intel.com>,
        "Doug Smythies" <dsmythies@...us.net>
Subject: RE: Performance of low-cpu utilisation benchmark regressed severely since 4.6

On 2017.04.20 18:18 Rafael wrote:
> On Thursday, April 20, 2017 07:55:57 AM Doug Smythies wrote:
>> On 2017.04.19 01:16 Mel Gorman wrote:
>>> On Fri, Apr 14, 2017 at 04:01:40PM -0700, Doug Smythies wrote:
>>>> Hi Mel,
>
> [cut]
>
>>> And the revert does help albeit not being an option for reasons Rafael
>>> covered.
>> 
>> New data point: Kernel 4.11-rc7  intel_pstate, powersave forcing the
>> load based algorithm: Elapsed 3178 seconds.
>> 
>> If I understand your data correctly, my load based results are the opposite of yours.
>> 
>> Mel: 4.11-rc5 vanilla: Elapsed mean: 3750.20 Seconds
>> Mel: 4.11-rc5 load based: Elapsed mean: 2503.27 Seconds
>> Or: 33.25%
>> 
>> Doug: 4.11-rc6 stock: Elapsed total (5 runs): 2364.45 Seconds
>> Doug: 4.11-rc7 force load based: Elapsed total (5 runs): 3178 Seconds
>> Or: -34.4%
>
> I wonder if you can do the same thing I've just advised Mel to do.  That is,
> take my linux-next branch:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git linux-next
>
> (which is new material for 4.12 on top of 4.11-rc7) and reduce
> INTEL_PSTATE_DEFAULT_SAMPLING_INTERVAL (in intel_pstate.c) in it by 1/2
> (force load-based if need be, I'm not sure what PM profile of your test system
> is).

I did not need to force load-based. I do not know how to figure it out from
an acpidump the way Srinivas does. I did a trace and figured out what algorithm
it was using from the data.

Reference test, before changing INTEL_PSTATE_DEFAULT_SAMPLING_INTERVAL:
3239.4 seconds.

Test after changing INTEL_PSTATE_DEFAULT_SAMPLING_INTERVAL:
3195.5 seconds.

By far, and with any code, I get the fastest elapsed time, of course next
to performance mode, but not by much, by limiting the test to only use
just 1 cpu: 1814.2 Seconds.
(performance governor, restated from a previous e-mail: 1776.05 seconds)

... Doug