linux-kernel - Re: [PATCH -tip] x86,perf: P4 PMU -- protect sensible procedures from preemption

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Message-ID: <20100506144854.GB5583@lenovo>
Date:	Thu, 6 May 2010 18:48:54 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH -tip] x86,perf: P4 PMU -- protect sensible procedures
	from preemption

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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