linux-kernel - Re: Kernel 4.7rc3 - Performance drop 30-40% for SPECjbb2005 and SPECjvm2008 benchmarks against 4.6 kernel

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Date:	Wed, 22 Jun 2016 10:25:19 +0200
From:	Jirka Hladky <jhladky@...hat.com>
To:	Branimir Maksimovic <branimir.maksimovic@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Kernel 4.7rc3 - Performance drop 30-40% for SPECjbb2005 and
 SPECjvm2008 benchmarks against 4.6 kernel

Hi Branimir,

I don't think that it's related. The regression has happened in one of
these two commits:

$ git log --pretty=oneline
e7904a28f5331c21d17af638cb477c83662e3cb6..6ecdd74962f246dfe8750b7bea481a1c0816315d
6ecdd74962f246dfe8750b7bea481a1c0816315d sched/fair: Generalize the
load/util averages resolution definition
2159197d66770ec01f75c93fb11dc66df81fd45b sched/core: Enable increased
load resolution on 64-bit kernels

Please see
https://bugzilla.kernel.org/show_bug.cgi?id=120481
for the details.

Jirka




On Wed, Jun 22, 2016 at 9:37 AM, Branimir Maksimovic
<branimir.maksimovic@...il.com> wrote:
> Could it be related to this:
>
> https://www.phoronix.com/scan.php?page=news_item&px=P-State-Possible-4.6-Regression
>
>
> On Thu, 16 Jun 2016 18:40:01 +0200
> Jirka Hladky <jhladky@...hat.com> wrote:
>
>> Hello,
>>
>> we see performance drop 30-40% for SPECjbb2005 and SPECjvm2008
>> benchmarks starting from 4.7.0-0.rc0 kernel compared to 4.6 kernel.
>>
>> We have tested kernels 4.7.0-0.rc1 and 4.7.0-0.rc3 and these are as
>> well affected.
>>
>> We have observed the drop on variety of different x86_64 servers with
>> different configuration (different CPU models, RAM sizes, both with
>> Hyper Threading ON and OFF, different NUMA configurations (2 and 4
>> NUMA nodes)
>>
>> Linpack and Stream benchmarks do not show any performance drop.
>>
>> The performance drop increases with higher number of threads. The
>> maximum number of threads in each benchmark is the same as number of
>> CPUs.
>>
>> We have opened a BZ to track the progress:
>> https://bugzilla.kernel.org/show_bug.cgi?id=120481
>>
>> You can find more details along with graphs and tables there.
>>
>> Do you have any hints which commit should we try to reverse?
>>
>> Thanks a lot!
>> Jirka
>