Re: [PATCH -tip] x86,perf: P4 PMU -- protect sensible proceduresfrom preemption

[Cyrill Gorcunov]

On Thu, May 06, 2010 at 09:45:24AM -0400, Steven Rostedt wrote:
...
> > > We want the one with the least runtime overhead. These are instrumentation
> > > routines, so we want to optimize them as much as possible.
> 
> 
> Yeah, my point was either disable preemption or keep the checks. In
> other words, if you don't disable preemption, do not use
> raw_smp_procesor_id(), because then we will not catch it if it changes
> in the future.
> 
> > ok, Ingo, dont apply this patch then for a while.
> 
> Send another patch, I'll test it again ;-)
> 
> -- Steve
> 
> 

Ingo, Steven, it seems we have potential preemtion available
in perf_event.c:validate_group:x86_pmu.schedule_events() which
is reached via syscall from userspace perf_event_open() call,
so get_cpu is still needed. But I'm a bit messed with call
graph at the moment :(

	-- Cyrill
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