linux-kernel - Re: [RFC] x86,perf: Implement minimal P4 PMU driver v14

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Date:	Fri, 12 Mar 2010 00:31:28 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Lin Ming <ming.m.lin@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Stephane Eranian <eranian@...gle.com>,
	Robert Richter <robert.richter@....com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] x86,perf: Implement minimal P4 PMU driver v14

On Thu, Mar 11, 2010 at 10:24:22PM +0100, Peter Zijlstra wrote:
> On Fri, 2010-03-12 at 00:15 +0300, Cyrill Gorcunov wrote:
> 
> > Perhaps something like the patch below (tested with kvm)? With this patch
> > we will actually waste ~4/8 bytes per PMU (intel,amd,p6) since this call
> > hits on p4 only, so I think perhaps better to use one x86 scheduler hook
> > instead of empty schedule_events() in PMU, hmm?
> > ---
> > 
> > x86,perf: Fix NULL deref on not assigned x86_pmu
> > 
> > In case of not assigned x86_pmu and software events
> > NULL dereference may being hit via x86_pmu::schedule_events
> > method.
> > 
> > Fix it by calling x86_pmu::schedule_events only if we
> > have one. Otherwise use general scheduler.
> > 
> > Also the former x86_schedule_events calls restored.
> 
> Hrm,.. not sure that makes sense, sure it might not crash anymore, but
> its not making much sense to compute anything if we don't have an
> initialized x86_pmu.
> 
> Doesn't adding something like:
> 
>   if (!x86_pmu_initialized())
>    return;
> 
> to hw_perf_group_sched_in() make more sense? We seem to do that for all
> these weak things except this one.
> 

As far as I see it'll not update tstamp_running then (in x86_event_sched_in).
Or I miss somethig?

	-- Cyrill
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