linux-kernel - Re: [RFC PATCH 0/3] perf: show package power consumption in perf

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Message-ID: <20100818124116.GA17957@console-pimps.org>
Date:	Wed, 18 Aug 2010 13:41:16 +0100
From:	Matt Fleming <matt@...sole-pimps.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Zhang Rui <rui.zhang@...el.com>,
	LKML <linux-kernel@...r.kernel.org>, mingo@...e.hu,
	robert.richter@....com, acme@...hat.com, paulus@...ba.org,
	dzickus@...hat.com, gorcunov@...il.com, fweisbec@...il.com,
	Lin Ming <ming.m.lin@...el.com>,
	"Brown, Len" <lenb@...nel.org>,
	Matthew Garrett <mjg59@...f.ucam.org>
Subject: Re: [RFC PATCH 0/3] perf: show package power consumption in perf

On Wed, Aug 18, 2010 at 02:25:29PM +0200, Peter Zijlstra wrote:
> On Wed, 2010-08-18 at 15:59 +0800, Zhang Rui wrote:
> > Hi, all,
> > 
> > RAPL(running average power limit) is a new feature which provides
> > mechanisms to enforce power consumption limit, on some new processors.
> > 
> > Generally speaking, by using RAPL, OS can set a power budget in a
> > certain time window, and let Hardware to throttle the processor
> > P/T-state to meet this energy limitation.
> > 
> > RAPL also provides a new MSR, i.e. MSR_PKG_ENERGY_STATUS, which reports
> > the total amount of energy consumed by the package.
> > 
> > I'm not sure if to support RAPL or not, but anyway, it sounds like a
> > good idea to export the energy status in perf.
> > 
> > So a new perf pmu and event to show the package energy consumed is
> > introduced in this patch.
> > 
> > Here is what I get after applying the three patches,
> > 
> > #./perf stat -e energy test
> > Performance counter stats for 'test':
> > 
> > 	202	Joules cost by package
> > 7.926001238	seconds time elapsed
> > 
> > 
> > Note that this patch set is made based on Peter's perf-pmu branch,
> > git://git.kernel.org/pub/scm/linux/kernel/git/peterz/linux-2.6-perf.git
> >  which provides better interfaces to register/unregister a new pmu.
> > 
> > any comment are welcome. :)
> 
> 
> Nice,.. however:
> 
>  - if it is a pure read-only counter without sampling support,
>    expose it as such, don't fudge in the hrtimer stuff. Simply
>    fail to create a sampling event.
> 
>    SH has the same problem for its 'normal' PMU, the solution is
>    to use event groups, Matt was looking at adding support to
>    perf-record for that, if creating a sampling event fails, fall
>    back to {hrtimer, $event} groups.

I had a quick look over the patches and Peter is right - the group
events stuff would probably fit quite well here. Unfortunately, due to
holidays and things, I haven't been able to get them finished
yet. I'll get on that ASAP.
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