linux-kernel - Re: [PATCH 3/5] MIPS/Perf-events: Check event state in validate

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Date:	Fri, 19 Nov 2010 12:27:31 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Will Deacon <will.deacon@....com>
Cc:	Deng-Cheng Zhu <dengcheng.zhu@...il.com>, ralf@...ux-mips.org,
	fweisbec@...il.com, linux-mips@...ux-mips.org,
	linux-kernel@...r.kernel.org, wuzhangjin@...il.com,
	paulus@...ba.org, mingo@...e.hu, acme@...hat.com
Subject: Re: [PATCH 3/5] MIPS/Perf-events: Check event state in
 validate_event()

On Fri, 2010-11-19 at 09:43 +0000, Will Deacon wrote:
> Hi Deng-Cheng,
> 
> On Thu, 2010-11-18 at 06:56 +0000, Deng-Cheng Zhu wrote:
> > Ignore events that are not for this PMU or are in off/error state.
> > 
> Sorry I didn't see this before, thanks for pointing out that you
> had included it for MIPS.
> 
> > Signed-off-by: Deng-Cheng Zhu <dengcheng.zhu@...il.com>
> > ---
> >  arch/mips/kernel/perf_event.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/arch/mips/kernel/perf_event.c b/arch/mips/kernel/perf_event.c
> > index 1ee44a3..9c6442a 100644
> > --- a/arch/mips/kernel/perf_event.c
> > +++ b/arch/mips/kernel/perf_event.c
> > @@ -486,7 +486,7 @@ static int validate_event(struct cpu_hw_events *cpuc,
> >  {
> >         struct hw_perf_event fake_hwc = event->hw;
> > 
> > -       if (event->pmu && event->pmu != &pmu)
> > +       if (event->pmu != &pmu || event->state <= PERF_EVENT_STATE_OFF)
> >                 return 0;
> > 
> >         return mipspmu->alloc_counter(cpuc, &fake_hwc) >= 0;
> 
> So this is the opposite of what we're doing on ARM. Our
> approach is to ignore events that are OFF (or in the ERROR
> state) or that belong to a different PMU. We do this by
> allowing them to *pass* validation (i.e. by returning 1 above).
> This means that we won't unconditionally fail a mixed event group.
> 
> x86 does something similar in the collect_events function.

Right, note that the generic code only allows mixing with software
events, so simply accepting them is ok as software events give the
guarantee they're always schedulable.
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