linux-kernel - Re: [PATCH 1/2] perf x86: Make intel_pmu_enable

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Date:	Thu, 15 Aug 2013 13:40:40 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 1/2] perf x86: Make intel_pmu_enable_all to enable only
 active events

On Tue, Aug 13, 2013 at 06:39:11PM +0200, Jiri Olsa wrote:
> Currently the intel_pmu_enable_all enables all possible
> events, which is not allways desired. One case (there'll
> be probably more) is:
> 
>   - event hits throttling threshold
>   - NMI stops event
>   - intel_pmu_enable_all starts it back on the NMI exit
> 


> +++ b/arch/x86/kernel/cpu/perf_event_intel.c
> @@ -912,11 +912,13 @@ static void intel_pmu_disable_all(void)
>  static void intel_pmu_enable_all(int added)
>  {
>  	struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
> +	u64 active_mask = *((u64*) cpuc->active_mask);
>  
>  	intel_pmu_pebs_enable_all();
>  	intel_pmu_lbr_enable_all();
>  	wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL,
> -			x86_pmu.intel_ctrl & ~cpuc->intel_ctrl_guest_mask);
> +			x86_pmu.intel_ctrl & ~cpuc->intel_ctrl_guest_mask
> +			& active_mask);

Garh.. you made my head hurt :-)

I think its a NOP; this is the global ctrl register but
intel_pmu_disable_event() writes PERFEVTSELx.EN = 0, so even if you
enable it in the global mask, the event should still be disabled.


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