lkml.org 
[lkml]   [2011]   [Jul]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH -tip, final] perf, x86: Add hw_watchdog_set_attr() in a sake of nmi-watchdog on P4

* Cyrill Gorcunov <gorcunov@gmail.com> wrote:

> perf, x86: P4 PMU - Add hw_watchdog_set_attr helper to simulate cpu-cycles counting in nmi-watchdog
>
> Because of constraints existed in Netburst PMU counting
> cpu cycles is allowed for one consumer only.
>
> If the kernel is booted up with nmi-watchdog enabled
> the watchdog become a consumer of such event and there
> is no more room left for "perf top" and friends (ie any
> attempts to count cpu cycles simultaneously with nmi-watchdog
> doomed to fail).

Hm, what is the symptom - 'perf top' reports nothing?

If multiple users request cycles then perf will time-share them -
this is what happens if you run many 'perf top' or 'perf stat'
sessions in parallel for example. For example i just tried to run six
separate 'perf top' in parallel - and all six worked fine.

So the question is, why does the NMI watchdog prevent 'perf top' from
working on a P4?

Thanks,

Ingo


\
 
 \ /
  Last update: 2011-07-05 15:13    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site