Re: CONFIG_NO_HZ breaks blktrace timestamps

[David Dillow]

On Thu, 2008-01-10 at 23:44 +0100, Guillaume Chazarain wrote:
> David Dillow <dillowda@xxxxxxxx> 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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/