Messages in this thread | | | Date | Fri, 30 Jun 2006 07:12:48 -0700 | From | Stephane Eranian <> | Subject | Re: [PATCH 10/17] 2.6.17.1 perfmon2 patch for review: PMU context switch |
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Andi,
On Fri, Jun 30, 2006 at 03:41:22PM +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'. >
The exclude-idle feature is an option you select when you create your cpu-wide session. By default, it is off.
> 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. > Yes, but that may not necessarily be troe of all architectures. At least with the option, the interfaces provides some guarantee.
> And on the other hand a lot of people especially want idle > accounting too and boot with idle=poll. Your explicit > code would likely defeat that. > > > As you realize, that means > > that we need to turn off when the idle thread is context switched > > in and turn it back on when it is switched off. > > Also x86-64 has idle notifiers for this if you really wanted > to do it properly. > That looks like a useful feature I could leverage but why is it just on x86-64 at the moment?
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