linux-kernel - Re: [RFC][PATCH 3/9] perf: export registerred pmus via sysfs

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Date:	Mon, 10 May 2010 18:26:35 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"eranian@...il.com" <eranian@...il.com>,
	"Gary.Mohr@...l.com" <Gary.Mohr@...l.com>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Paul Mackerras <paulus@...ba.org>,
	"David S. Miller" <davem@...emloft.net>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Paul Mundt <lethal@...ux-sh.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 3/9] perf: export registerred pmus via sysfs

On Mon, 2010-05-10 at 18:18 +0800, Peter Zijlstra wrote:
> On Mon, 2010-05-10 at 18:11 +0800, Lin Ming wrote:
> > On Mon, 2010-05-10 at 17:40 +0800, Peter Zijlstra wrote:
> > > On Mon, 2010-05-10 at 17:27 +0800, Lin Ming wrote:
> > > > Export pmus via sysfs /sys/devices/system/cpu/pmus/0...N
> > > > The file name is the pmu id, ie, /sys/devices/system/cpu/pmus/N
> > > > represents pmu id N.
> > > > So perf tool can use it to initialize perf_event_attr. 
> > > 
> > > Why create a whole new directory, why not:
> > > 
> > >  /sys/devices/system/cpu/cpuN/pmu_id ?
> > 
> > 
> > Do you mean /sys/devices/system/cpu/cpuN/pmu_id contain all ids?
> > 
> > For example, each cpu has 4 pmus and the file pmu_id shows something
> > like,
> > 
> > #cat /sys/devices/system/cpu/cpu0/pmu_id
> > 0 1 2 3
> 
> No, I'm assuming there is only 1 PMU per CPU. Corey is the expert on
> crazy hardware though, but I think the sanest way is to extend the CPU
> topology if there's more structure to it.

But our goal is to support multiple pmus, don't we need to assume there
are more than 1 PMU per CPU?

> 
> It simply doesn't make sense to have multiple PMU IDs on a single
> topology entry, how would you choose?

How about
/sys/devices/system/cpu/cpuN/pmu_0
/sys/devices/system/cpu/cpuN/pmu_1
/sys/devices/system/cpu/cpuN/pmu_2
/sys/devices/system/cpu/cpuN/pmu_3
....?


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