linux-kernel - Re: [tip:perf/urgent] perf/x86/cqm: Fix CQM handling of grouping events into a cache

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Date:	Wed, 23 Mar 2016 20:14:38 +0000
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Vikas Shivappa <vikas.shivappa@...ux.intel.com>
Cc:	hpa@...or.com, eranian@...gle.com, linux-kernel@...r.kernel.org,
	tony.luck@...el.com, brgerst@...il.com, peterz@...radead.org,
	bp@...en8.de, tglx@...utronix.de, dsahern@...il.com,
	dvlasenk@...hat.com, jolsa@...hat.com, luto@...capital.net,
	mingo@...nel.org, acme@...hat.com, torvalds@...ux-foundation.org,
	namhyung@...nel.org, vincent.weaver@...ne.edu,
	alexander.shishkin@...ux.intel.com,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/urgent] perf/x86/cqm: Fix CQM handling of grouping
 events into a cache_group

On Mon, 21 Mar, at 11:14:37AM, Vikas Shivappa wrote:
> 
> 
> Before MBM , the below condition was never hit because we had only one event ?
> 
> -       if (a->hw.target == b->hw.target)
> +       if (a->hw.target == b->hw.target) {
> +               b->hw.is_group_event = true;
> 
> We are trying to address this for cases where different MBM(local or total)
> and cqm events are grouped into one RMID.
 
I can't test these changes, so I'm only working from memory, but I
seem to recall that this condition is hit if monitoring simultaneously
from two invocations of perf. It's also possible to have pid/tid
groups overlapping, and that needs to be handled.

> Which is the case which led to duplicate values ?

Good question. Try monitoring a multithread process with these changes
and see if you get duplicate values reported.