linux-kernel - Re: [PATCH 1/2] pebs, x86: Make sure to really disable PEBS

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Message-ID: <1345457400.23018.28.camel@twins>
Date:	Mon, 20 Aug 2012 12:10:00 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	mingo@...e.hu, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 1/2] pebs, x86: Make sure to really disable PEBS

On Sat, 2012-08-18 at 09:15 -0700, Andi Kleen wrote:
> From: Andi Kleen <ak@...ux.intel.com>
> 
> When disabling a PEBS event we need to check the old value
> to determine if PEBS was running. Otherwise the last PEBS value
> could be kept running.
> 
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> ---
>  arch/x86/kernel/cpu/perf_event_intel_ds.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/perf_event_intel_ds.c b/arch/x86/kernel/cpu/perf_event_intel_ds.c
> index e38d97b..db49ab3 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel_ds.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel_ds.c
> @@ -438,9 +438,10 @@ void intel_pmu_pebs_disable(struct perf_event *event)
>  {
>  	struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
>  	struct hw_perf_event *hwc = &event->hw;
> +	u64 old = cpuc->pebs_enabled;
>  
>  	cpuc->pebs_enabled &= ~(1ULL << hwc->idx);
> -	if (cpuc->enabled)
> +	if (old)

cpuc->enabled != cpuc->pebs_enabled

>  		wrmsrl(MSR_IA32_PEBS_ENABLE, cpuc->pebs_enabled);
>  
>  	hwc->config |= ARCH_PERFMON_EVENTSEL_INT;

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