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

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Message-ID: <2640598.7kLQfP2zoQ@aspire.rjw.lan>
Date:   Fri, 21 Apr 2017 03:17:39 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Doug Smythies <dsmythies@...us.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>
Subject: Re: Performance of low-cpu utilisation benchmark regressed severely since 4.6

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).

Thanks,
Rafael