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

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Message-ID: <20160425200512.GN3448@twins.programming.kicks-ass.net>
Date:	Mon, 25 Apr 2016 22:05:12 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vikas Shivappa <vikas.shivappa@...el.com>
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>, 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, Apr 25, 2016 at 09:44:53AM -0700, Vikas Shivappa wrote:
> 
> 
> 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

This is naturally handled by the scheme I outlined in the other patch.