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

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Date:	Fri, 27 Apr 2012 08:23:50 -0700
From:	Dave Johansen <davejohansen@...il.com>
To:	Yong Zhang <yong.zhang0@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: High CPU usage of scheduler?

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
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