Re: [PATCH 10/17] 2.6.17.1 perfmon2 patch for review: PMU context switch

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Friday 30 June 2006 20:33, Chuck Ebbert wrote:
> In-Reply-To: <[email protected]>
> 
> On Fri, 30 Jun 2006 15:41:22 +0200, Andi Kleen wrote:
> 
> > > So why do we need care about context switch in cpu-wide mode?
> > > It is because we support a mode where the idle thread is excluded
> > > from cpu-wide monitoring. This is very useful to distinguish 
> > > 'useful kernel work' from 'idle'. 
> > 
> > I don't quite see the point because on x86 the PMU doesn't run
> > during C states anyways. So you get idle excluded automatically.
> 
> Looks like it does run:

I'm pretty sure it doesn't. You can see it by watching 
the frequency of the perfctr mode NMI watchdog in /proc/interrupts 
under different loads.

When the system is idle the frequency goes down and increases
when the system is busy. I also got confirmation of this behaviour
from both Intel and AMD. C states > 0 are not supposed to run
the performance counters.

Are you sure you didn't boot with poll=idle? Otherwise something must
be wrong with your measurements.

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

[Index of Archives]     [Kernel Newbies]     [Netfilter]     [Bugtraq]     [Photo]     [Stuff]     [Gimp]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Video 4 Linux]     [Linux for the blind]     [Linux Resources]
  Powered by Linux