linux-kernel - Re: [4.17 regression] Performance drop on kernel-4.17 visible on Stream, Linpack and NAS parallel benchmarks

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Date:   Fri, 7 Sep 2018 10:09:07 +0200
From:   Jirka Hladky <jhladky@...hat.com>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Kamil Kolakowski <kkolakow@...hat.com>,
        Jakub Racek <jracek@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org
Subject: Re: [4.17 regression] Performance drop on kernel-4.17 visible on
 Stream, Linpack and NAS parallel benchmarks

> Maybe 305c1fac3225dfa7eeb89bfe91b7335a6edd5172. That introduces a weird
> condition in terms of idle CPU handling that has been problematic.


We will try that, thanks!

>  I would suggest contacting Srikar directly.


I will do that right away. Whom should I put on Cc? Just you and
linux-kernel@...r.kernel.org ? Should I put Ingo and Peter on Cc as
well?

$scripts/get_maintainer.pl -f kernel/sched
Ingo Molnar <mingo@...hat.com> (maintainer:SCHEDULER)
Peter Zijlstra <peterz@...radead.org> (maintainer:SCHEDULER)
linux-kernel@...r.kernel.org (open list:SCHEDULER)

Jirka

On Thu, Sep 6, 2018 at 2:58 PM, Mel Gorman <mgorman@...hsingularity.net> wrote:
> On Thu, Sep 06, 2018 at 10:16:28AM +0200, Jirka Hladky wrote:
>> Hi Mel,
>>
>> we have results with 2d4056fafa196e1ab4e7161bae4df76f9602d56d reverted.
>>
>>   * Compared to 4.18, there is still performance regression -
>> especially with NAS (sp_C_x subtest) and SPECjvm2008. On 4 NUMA
>> systems, regression is around 10-15%
>>   * Compared to 4.19rc1 there is a clear gain across all benchmarks around 20%
>>
>
> Ok.
>
>> While reverting 2d4056fafa196e1ab4e7161bae4df76f9602d56d has helped a
>> lot there is another issue as well. Could you please recommend some
>> commit prior to 2d4056fafa196e1ab4e7161bae4df76f9602d56d to try?
>>
>
> Maybe 305c1fac3225dfa7eeb89bfe91b7335a6edd5172. That introduces a weird
> condition in terms of idle CPU handling that has been problematic.
>
>> Regarding the current results, how do we proceed? Could you please
>> contact Srikar and ask for the advice or should we contact him
>> directly?
>>
>
> I would suggest contacting Srikar directly. While I'm working on a
> series that touches off some similar areas, there is no guarantee it'll
> be a success as I'm not primarily upstream focused at the moment.
>
> Restarting the thread would also end up with a much more sensible cc
> list.
>
> --
> Mel Gorman
> SUSE Labs