linux-kernel - Re: [RFC PATCH 2/2] perf stat: Use event group to simulate PMI on PMI-less hardware counter

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Date:	Wed, 10 Nov 2010 22:45:19 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Matt Fleming <matt@...sole-pimps.org>,
	"Zhang, Rui" <rui.zhang@...el.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [RFC PATCH 2/2] perf stat: Use event group to simulate PMI on
 PMI-less hardware counter

On Wed, 2010-11-10 at 20:21 +0800, Peter Zijlstra wrote:
> On Wed, 2010-11-10 at 14:15 +0800, Lin Ming wrote:
> > Some hardware counters(for example, Intel RAPL) can't generate interrupt
> > when overflow. So we need to simulate the interrupt to periodically
> > record the counter values. Otherwise, the counter may overflow and the
> > wrong value is read.
> > 
> > This patch uses event group to simulate PMI as suggested by Peter
> > Zijlstra, http://marc.info/?l=linux-kernel&m=128220854801819&w=2
> > 
> > create_group_counters() will create a group with 2 events, one hrtimer
> > based event as the group leader, and the other event to count. The
> > hrtimer is fired periodically, so the sibling event can record its
> > counter value periodically as well.
> 
> I'm terribly confused here....
> 
>  - you introduce perf_event_attr:pmi_simulate, but then you never
> implement it -- nor do we need it afaict.

Someone need to simluate pmi will use it in future.

> 
> 
>  - you use grouped counters for perf-stat, perf-stat doesn't use
> sampling so I don't see a need to group events to simulate the PMI.
> 

Aha, sorry, actually, I mean to periodically read the PMI-less counter
and reset it to zero each time to avoid overflow.

Well, seems I have done this in the wrong way.
Let me re-think about it.


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