linux-kernel - Re: [PATCH V4 03/16] perf, x86: use context switch callback to flush LBR stack

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Message-ID: <20140702090638.GU6758@twins.programming.kicks-ass.net>
Date:	Wed, 2 Jul 2014 11:06:38 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Yan, Zheng" <zheng.z.yan@...el.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org, acme@...radead.org,
	eranian@...gle.com, andi@...stfloor.org
Subject: Re: [PATCH V4 03/16] perf, x86: use context switch callback to flush
 LBR stack

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;
> +	}
> +}

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