On Mon, Jun 30, 2014 at 04:50:40PM +0800, Yan, Zheng wrote:
> @@ -185,6 +185,23 @@ void intel_pmu_lbr_enable(struct perf_event *event)
>  		return;
>  
>  	/*
> +	 * It is necessary to flush the stack on context switch. This happens
> +	 * when the branch stack does not tag its entries with the pid of the
> +	 * current task.

Did you mean to say: "This happens _because_ the branch stack does not
tag its entries with the pid of the current task." ?

> +	 */
> +	if (sched_in) {
> +		intel_pmu_lbr_reset();
> +		cpuc->lbr_context = ctx;
> +	}
> +}