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SubjectRe: [4.17 regression] Performance drop on kernel-4.17 visible on Stream, Linpack and NAS parallel benchmarks
Hi Mel,

we have tried to revert following 2 commits:

305c1fac3225
2d4056fafa196e1ab

We had to revert 10864a9e222048a862da2c21efa28929a4dfed15 as well.

The performance of the kernel was better than when only
2d4056fafa196e1ab was reverted but still worse than the performance of
4.18 kernel.

Since the patch series from Srikar shows very good results we would
wait till it's merged to mainline kernel and stop the bisecting
efforts for now. Your patch series sched-numa-fast-crossnode-v1r12 (on
top of 4.18) is giving in some cases slightly better results than
Srikar's series so it would be really great if both series could be
merged together. Removing NUMA migration rate limit helps performance.

Thanks a lot for your help on this!
Jirka


On Fri, Sep 7, 2018 at 10:09 AM, Jirka Hladky <jhladky@redhat.com> wrote:
>> 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@vger.kernel.org ? Should I put Ingo and Peter on Cc as
> well?
>
> $scripts/get_maintainer.pl -f kernel/sched
> Ingo Molnar <mingo@redhat.com> (maintainer:SCHEDULER)
> Peter Zijlstra <peterz@infradead.org> (maintainer:SCHEDULER)
> linux-kernel@vger.kernel.org (open list:SCHEDULER)
>
> Jirka
>
> On Thu, Sep 6, 2018 at 2:58 PM, Mel Gorman <mgorman@techsingularity.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

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