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

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Date:	Thu, 03 Jul 2014 13:44:48 +0800
From:	"Yan, Zheng" <zheng.z.yan@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
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 07/02/2014 05:06 PM, Peter Zijlstra wrote:
> 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." ?

yes. The comment is copied from comments of perf_branch_stack_sched_in()

Regards
Yan, Zheng

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

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