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Date: Thu, 6 May 2010 18:48:54 +0400
From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@elte.hu>, Frederic Weisbecker <fweisbec@gmail.com>,
       LKML <linux-kernel@vger.kernel.org>,
       Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH -tip] x86,perf: P4 PMU -- protect sensible procedures
	from preemption
Message-ID: <20100506144854.GB5583@lenovo>
References: <20100505150740.GB5686@lenovo> <20100505165731.GA6320@nowhere> <20100505174234.GH5686@lenovo> <20100506064453.GI1172@elte.hu> <w2vaa79d98a1005060039ua7dd1b0t952fcd8662d4d759@mail.gmail.com> <20100506074231.GA8625@elte.hu> <n2maa79d98a1005060045ke0f87f4aw8b86da0440a019b3@mail.gmail.com> <1273153525.22438.39.camel@gandalf.stny.rr.com>
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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