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From Igor Galić <i.ga...@brainsware.org>
Subject Re: High idle cpu utilization on RHEL6
Date Sun, 02 Oct 2011 18:21:41 GMT


----- Original Message -----
> On Wed, Sep 28, 2011 at 3:35 PM, Brian Geffon <briangeffon@gmail.com>
> wrote:
> 
> > Hi,
> > I'm encountering something strange with ATS3.0.1 on Red Hat
> > Enterprise
> > Linux 6, using a vanilla build with no modules enabled and the
> > default
> > records.config /w zero entries in the remap file, ATS is idling at
> > very high
> > CPU (around 15-20%).
> >
> > root     13509  0.0  0.0  58512  2392 ?        Ss   19:15   0:00
> > /usr/local/ats3.0.1plain//bin/traffic_cop
> > nobody   13511  0.1  0.0 480072 16632 ?        Sl   19:15   0:00
> > /usr/local/ats3.0.1plain/bin/traffic_manager
> > nobody   13521 ***16.9***  0.1 1584628 114224 ?      Sl   19:15
> >   2:06
> > /usr/local/ats3.0.1plain/bin/traffic_server -M -A,7:X
> >
> > So I used strace to try to determine what might be causing this,
> > and here
> > is what i've found:
> >
> > [root@machine]# strace -c -p 13521
> > Process 13521 attached - interrupt to quit
> > ^CProcess 13521 detached
> > % time     seconds  usecs/call     calls    errors syscall
> > ------ ----------- ----------- --------- --------- ----------------
> > 100.00    3.589451         796      4510           epoll_wait
> > ------ ----------- ----------- --------- --------- ----------------
> > 100.00    3.589451                  4510           total
> > [root@machine]#
> >
> >
> > It appears that it's entirely epoll_wait, and each call is taking
> > 796
> > microseconds! So I have to concerns with this, first, why would
> > epoll_wait
> > take such a long amount of time, 796 microseconds seems like a long
> > time,
> > and more importantly, how could it possibly be called so
> > frequently, does
> > ATS use a short timeout when doing epoll_waits?
> >
> > I would really appreciate any feedback regarding this, has anyone
> > else
> > experienced this? Is there anywhere else I might look to determine
> > the cause
> > of this? Could this be classified as _normal_ behavior?
> >
> >
> >
> It is working as designed. The epoll timeout is set to 0 or 10 msec
> on
> linux. Could there be very little or no load going through this
> instance?
> That would explain why you are only seeing epoll_wait. In that case
> there
> isn't really anything wrong, the process is just burning through
> epoll_waits
> looking for something to do when nothing is available. Once the
> process
> starts taking enough traffic, you will start to see user space and
> other
> kernel functions start to take cpu time.

That still doesn't quite explain the high load on an Idle system.

Brian: Do you happen to have SELinux enabled?

>  Sridhar

i

-- 
Igor Galić

Tel: +43 (0) 664 886 22 883
Mail: i.galic@brainsware.org
URL: http://brainsware.org/
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