linux-kernel - Re: [PATCH 5/9] perf: Adding sysfs group format attribute for pmu device

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Date:	Wed, 01 Feb 2012 15:18:52 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Corey Ashford <cjashfor@...ux.vnet.ibm.com>, acme@...hat.com,
	mingo@...e.hu, paulus@...ba.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/9] perf: Adding sysfs group format attribute for pmu
 device

On Wed, 2012-02-01 at 14:13 +0100, Jiri Olsa wrote:
> > Are you are suggesting that a single event could use multiple groups
> > because they may share some common fields, such as the event code?  If
> > so, I think that might be confusing.   I think it would be better to
> > have every group fully lay out the bits in the config{,1,2} fields so
> > that you only need to specify one group per event, even if that leads to
> > some redundancy (e.g. group1..n all have an eventcode field.)
> 
> ok, it'd be the 'cpu::group1/config=1,config1=2,config2=3/u' then..
> 
> but let's see what Peter thinks about this, since he first suggested
> to 'fix' this by having separate pmu drivers.. not format groups :) 

I'm not convinced we need the whole grouping thing. Even x86 might have
overlapping definitions, even for a single PMU (config1 contents will
radically differ depending on the actual events used for instance).

All we should do is warn the user when overlapping masks are used in a
single event definition and other than that just do as they tell us.

PMUs can always do an informal namespace thing if really needed, eg. by
using a consistent prefix.

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