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

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Message-ID: <20180906125843.GC1719@techsingularity.net>
Date:   Thu, 6 Sep 2018 13:58:43 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Jirka Hladky <jhladky@...hat.com>
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

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