linux-kernel - Re: High CPU usage of scheduler?

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Message-ID: <CAAcYxUe7RmWm9AhFpjPAiaW9zirYJbzm1wtAMJ=LUpX-kskp9w@mail.gmail.com>
Date:	Mon, 30 Apr 2012 22:11:45 -0700
From:	Dave Johansen <davejohansen@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Re: High CPU usage of scheduler?

On Fri, Apr 27, 2012 at 8:23 AM, Dave Johansen <davejohansen@...il.com> wrote:
> On Thu, Apr 26, 2012 at 8:10 PM, Yong Zhang <yong.zhang0@...il.com> wrote:
>>
>> On Thu, Apr 26, 2012 at 03:08:51PM -0700, Dave Johansen wrote:
>> > I am looking into moving an application from RHEL 5 to RHEL 6 and I
>> > noticed an unexpected increase in CPU usage. A little digging has led
>> > me to believe that the scheduler may be the culprit.
>> >
>> > I created the attached test_select_work.c file to test this out. I
>> > compiled it with the following command on RHEL 5:
>> >
>> > cc test_select_work.c -O2 -DSLEEP_TYPE=0 -Wall -Wextra -lm -lpthread
>> > -o test_select_work
>>
>> Hmm...Do both RHEL 5 and RHEL 6 have high resolution timer enabled?
>>
>> If not, could you please try to boot the one which enable high resolution
>> timer with 'highres=off' to see if things change?
>
> Yes, RHEL 6 has CONFIG_HIGH_RES_TIMERS=y. I rebooted and used the
> 'highres=off' in grub and got the following results:
>
>   ./test_select_work 1000 10000 300 4
>   time_per_iteration: min: 3130.1 us avg: 3152.2 us max: 3162.2 us
> stddev: 15.0 us
>   ./test_select_work 1000 10000 300 8
>   time_per_iteration: min: 4314.6 us avg: 4407.9 us max: 4496.3 us
> stddev: 60.6 us
>   ./test_select_work 1000 10000 300 40
>   time_per_iteration: min: 8901.7 us avg: 9056.5 us max: 9121.3 us
> stddev: 57.5 us
>
> Any other info that might be helpful?
>
> Thanks,
> Dave

I made some improvements to the program to make comparisons a bit
easier and the standard deviation a bit more meaningful. It is
available in a git repo at git://github.com/daveisfera/test_sleep.git

I tried sending results from running this updated program on several
OS versions, but it must have been rejected by the filters. The info
can be found in the bugzilla:
https://bugzilla.redhat.com/show_bug.cgi?id=812148

Is there any more data I can gather or tests that I can run that can
help diagnose this problem?

Thanks in advance for any help,
Dave
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