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SubjectRe: CONFIG_NO_HZ breaks blktrace timestamps
On Thu, Jan 10 2008, David Dillow wrote:
>
> On Thu, 2008-01-10 at 23:44 +0100, Guillaume Chazarain wrote:
> > David Dillow <dillowda@ornl.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 for reporting this. Guillaume, did you write this patch? We need
to get it into 2.6.24-rc7 asap. Let me know if I should take care of
that, or if it's already queued up elsewhere.

--
Jens Axboe



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