linux-kernel - Re: sched : performance regression 24% between 4.4rc4 and 4.3 kernel

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Message-ID: <CAE4VaGDsf8gbWdMJaUNbt7s6MrYX931982h=AvUxn9+OSKX0Zw@mail.gmail.com>
Date:	Tue, 15 Dec 2015 09:49:28 +0100
From:	Jirka Hladky <jhladky@...hat.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Mike Galbraith <umgwanakikbuti@...il.com>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: sched : performance regression 24% between 4.4rc4 and 4.3 kernel

Hi Rik,

I have reviewed the data and you are right. The trouble is that even
with 4.3 kernel there is 20% change that results will be bad. I have
repeated tests 100 times on 4.3 kernel over the night. In 20 cases I
see that runtime went up from 12 seconds to 28 seconds due to the
wrong NUMA placement. I will try to replay the bisect once again.

Jirka

On Tue, Dec 15, 2015 at 3:12 AM, Rik van Riel <riel@...hat.com> wrote:
> On 12/14/2015 06:52 PM, Jirka Hladky wrote:
>> Hi all,
>>
>> I have the results of bisecting:
>>
>> first bad commit: [973759c80db96ed4b4c5cb85ac7d48107f801371] Merge tag
>> 'v4.3-rc1' into sched/core, to refresh the branch
>>
>> Could you please have a look at this commit why it has caused the
>> performance regression when running 4 stream benchmarks in parallel on 4
>> NUMA node server?
>
> That is a merge commit. It contains no actual code changes.
>
>> Please let me know if you need additional data. git bisect log is bellow.
>
> It looks like "git bisect" may have led you astray.
>
> I am not sure what debugging tool to use to figure out which
> of the patches from some merged-in branch caused the issue,
> but hopefully one of the people reading this email know a trick.
>
> --
> All rights reversed
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