linux-kernel - Re: CONFIG_NO_HZ breaks blktrace timestamps

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Date:	Thu, 10 Jan 2008 22:04:21 -0500
From:	David Dillow <dillowda@...l.gov>
To:	Guillaume Chazarain <guichaz@...oo.fr>
Cc:	linux-kernel@...r.kernel.org, linux-btrace@...r.kernel.org,
	mingo@...hat.com, tglx@...utronix.de
Subject: Re: CONFIG_NO_HZ breaks blktrace timestamps


On Thu, 2008-01-10 at 23:44 +0100, Guillaume Chazarain wrote:
> David Dillow <dillowda@...l.gov> wrote:
> 
> > At the moment, I'm not sure how to track this farther, or how to fix it
> > properly. Any advice would be appreciated.
> 
> Just out of curiosity, could you try the appended cumulative patch and
> report .clock_warps, .clock_overflows and .clock_underflows as you did.

With those patches, CONFIG_NO_HZ works just fine.

Patched kernel, nohz=off:
now at 214257.820809 msecs
  .clock                         : 214212.727559
  .idle_clock                    : 0.000000
  .prev_clock_raw                : 244569.402345
  .clock_warps                   : 0
  .clock_overflows               : 577
  .clock_underflows              : 213887
  .clock_deep_idle_events        : 4
  .clock_max_delta               : 0.999830

Patched kernel, nohz=on:
now at 248931.524381 msecs
  .clock                         : 248745.808465
  .idle_clock                    : 0.000000
  .prev_clock_raw                : 270911.098507
  .clock_warps                   : 0
  .clock_overflows               : 69
  .clock_underflows              : 784
  .clock_deep_idle_events        : 4
  .clock_max_delta               : 100.639397

Running my disk test, blktrace is getting the proper timestamps now with
CONFIG_NO_HZ.

Thanks!
-- 
Dave Dillow
National Center for Computational Science
Oak Ridge National Laboratory
(865) 241-6602 office

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