linux-kernel - Re: [PATCH V4 07/16] perf, x86: track number of events that use LBR callstack

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Date:	Mon, 07 Jul 2014 14:36:36 +0800
From:	"Yan, Zheng" <zheng.z.yan@...el.com>
To:	linux-kernel@...r.kernel.org
CC:	a.p.zijlstra@...llo.nl, mingo@...nel.org, acme@...radead.org,
	eranian@...gle.com, andi@...stfloor.org
Subject: Re: [PATCH V4 07/16] perf, x86: track number of events that use LBR
 callstack

please ignore this patch

On 07/07/2014 02:28 PM, Yan, Zheng wrote:
> When enabling/disabling an event, check if the event uses the LBR
> callstack feature, adjust the LBR callstack usage count accordingly.
> Later patch will use the usage count to decide if LBR stack should
> be saved/restored.
> 
> Signed-off-by: Yan, Zheng <zheng.z.yan@...el.com>
> ---
>  arch/x86/kernel/cpu/perf_event_intel_lbr.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> index 9a94fff..66969cb 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> @@ -198,9 +198,15 @@ void intel_pmu_lbr_sched_task(struct perf_event_context *ctx, bool sched_in)
>  	}
>  }
>  
> +static inline bool branch_user_callstack(unsigned br_sel)
> +{
> +	return (br_sel & X86_BR_USER) && (br_sel & X86_BR_CALL_STACK);
> +}
> +
>  void intel_pmu_lbr_enable(struct perf_event *event)
>  {
>  	struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
> +	struct x86_perf_task_context *task_ctx;
>  
>  	if (!x86_pmu.lbr_nr)
>  		return;
> @@ -214,6 +220,10 @@ void intel_pmu_lbr_enable(struct perf_event *event)
>  	}
>  	cpuc->br_sel = event->hw.branch_reg.reg;
>  
> +	task_ctx = event->ctx ? event->ctx->task_ctx_data : NULL;
> +	if (branch_user_callstack(cpuc->br_sel))
> +		task_ctx->lbr_callstack_users++;
> +
>  	cpuc->lbr_users++;
>  	if (cpuc->lbr_users == 1)
>  		perf_sched_cb_enable(event->ctx->pmu);
> @@ -222,10 +232,15 @@ void intel_pmu_lbr_enable(struct perf_event *event)
>  void intel_pmu_lbr_disable(struct perf_event *event)
>  {
>  	struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
> +	struct x86_perf_task_context *task_ctx;
>  
>  	if (!x86_pmu.lbr_nr)
>  		return;
>  
> +	task_ctx = event->ctx ? event->ctx->task_ctx_data : NULL;
> +	if (branch_user_callstack(cpuc->br_sel))
> +		task_ctx->lbr_callstack_users--;
> +
>  	cpuc->lbr_users--;
>  	WARN_ON_ONCE(cpuc->lbr_users < 0);
>  
> 

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