linux-kernel - Re: [PATCH 3/4] perf/x86/mbm: Fix mbm counting when RMIDs are reused

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Date:	Mon, 25 Apr 2016 09:44:53 -0700 (PDT)
From:	Vikas Shivappa <vikas.shivappa@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
	tony.luck@...el.com, "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
	"Yu, Fenghua" <fenghua.yu@...el.com>, vikas.shivappa@...el.com,
	x86@...nel.org, linux-kernel@...r.kernel.org, hpa@...or.com,
	tglx@...utronix.de, mingo@...nel.org, h.peter.anvin@...el.com
Subject: Re: [PATCH 3/4] perf/x86/mbm: Fix mbm counting when RMIDs are
 reused

On Mon, 25 Apr 2016, Peter Zijlstra wrote:

> On Fri, Apr 22, 2016 at 05:27:20PM -0700, Vikas Shivappa wrote:
>> When multiple instances of perf reuse RMID, then we need to start
>> counting for each instance rather than reporting the current RMID count.
>> This patch adds a st_count(start count) per event to track the same.
>
> what?
>

Will fix the comit log :

When multiple instances of perf reuse RMID for the same PID, then we need to 
start counting from zero for each new event, rather than reporting the current 
RMID. This patch adds a st_count(start count) per event to track the same.

For ex:
1.RMID1's total_bytes is 100MB for event1(PID1)
2.another perf instance starts measuring the same PID1 with event2. We reuse 
RMID1 as the PID1 is already counted.
3.event2 stores st_count as 100MB.
4.After some time, when user wants to count event2 and say RMID1's current 
total_bytes 110MB, we report 110MB - 100MB = 10MB

Thanks,
Vikas