linux-kernel - Re: x86_pmu_start WARN

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Message-ID: <alpine.DEB.2.10.1402201438480.24360@vincent-weaver-1.um.maine.edu>
Date:	Thu, 20 Feb 2014 14:46:17 -0500 (EST)
From:	Vince Weaver <vincent.weaver@...ne.edu>
To:	Vince Weaver <vincent.weaver@...ne.edu>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: x86_pmu_start WARN_ON.

On Thu, 20 Feb 2014, Vince Weaver wrote:

> On Thu, 20 Feb 2014, Vince Weaver wrote:
> 
> > Might be relevant: check the last_cpu values.  Right before the above
> > it looks like the thread gets moved from CPU 1 to CPU 0
> > (possibly as a result of the long chain started with the
> > close() of the tracepoint event),
> > so the problem NMI watchdog event being enabled is a different one than 
> > the one that was disabled just before.
> 
> so is this a false warning?  If you get scheduled to a new CPU
> and there's an already running CPU-wide event, is that OK?
> 
> Or should x86_pmu_disable() be setting PERF_HES_STOPPED on all events?
> It looks like other architectures are (such as armpmu_stop() ).

an actually I take that back, other architectures don't.

It's just confusing how
	perf_pmu_disable()
		calls
	pmu->pmu_disable()

	which on arm is:
		armpmu_disable()
	which calls:
		armpmu->stop()
	which is *not* the same as:
		armpmu_stop()
	but is actually armpmu->pmu->stop()

Urgh.

Vince
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