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:   Tue, 17 Jul 2018 11:03:30 +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 Tue, Jul 17, 2018 at 10:45:51AM +0200, Jirka Hladky wrote:
> Hi Mel,
> 
> we have compared 4.18 + git://
> git.kernel.org/pub/scm/linux/kernel/git/mel/linux.git
> sched-numa-fast-crossnode-v1r12 against 4.16 kernel and performance results
> look very good!
> 

Excellent, thanks to both Kamil and yourself for collecting the data.
It's helpful to have independent verification.

> We see performance gains about 10-20% for SPECjbb2005. NAS results are a
> little bit noisy but show overall performance gains as well (total runtime
> for reduced from 6 hours 34 minutes to 6 hours 26 minutes to give you a
> specific example).

Great.

> The only benchmark showing a slight regression is stream
> - but the regression is just a few percents ( upto 10%) and I think it's
> not a real concern given that it's an artificial benchmark.
> 

Agreed.

> How is your testing going? Do you think
> that sched-numa-fast-crossnode-v1r12 series can make it into the 4.18?
> 

My own testing completed and the results are within expectations and I
saw no red flags. Unfortunately, I consider it unlikely they'll be merged
for 4.18. Srikar Dronamraju's series is likely to need another update
and I would need to rebase my patches on top of that. Given the scope
and complexity, I find it unlikely they would be accepted for an -rc,
particularly this late of an rc. Whether we hit the 4.19 merge window or
not will depend on when Srikar's series gets updated.

> Thanks a lot for your efforts to improve the performance!

My pleasure.

-- 
Mel Gorman
SUSE Labs