linux-kernel - Re: [RFC][PATCH v2 06/11] perf: core, export pmus via sysfs

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Message-Id: <1274236496.3603.22.camel@minggr.sh.intel.com>
Date:	Wed, 19 May 2010 10:34:55 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Greg KH <greg@...ah.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Paul Mundt <lethal@...ux-sh.org>,
	"eranian@...il.com" <eranian@...il.com>,
	"Gary.Mohr@...l.com" <Gary.Mohr@...l.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>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Will Deacon <will.deacon@....com>,
	Maynard Johnson <mpjohn@...ibm.com>,
	Carl Love <carll@...ibm.com>,
	Kay Sievers <kay.sievers@...y.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH v2 06/11] perf: core, export pmus via sysfs

On Wed, 2010-05-19 at 04:05 +0800, Greg KH wrote:
> On Wed, May 19, 2010 at 01:46:42AM +0000, Lin Ming wrote:
> > Now only exports cpu hardware events.
> > 
> > For each PMU, there are 2 sysfs dirs: event_source and events.
> > 
> > For example,
> > /sys/devices/system/cpu/event_source/
> > /sys/devices/system/cpu/events/
> > 
> > $ tree /sys/devices/system/cpu/event_source/
> > /sys/devices/system/cpu/event_source/
> > `-- id
> > 
> > $ tree /sys/devices/system/cpu/events/
> > /sys/devices/system/cpu/events/
> > |-- L1-dcache-load-misses
> > |   |-- event_source -> ../../event_source
> 
> What is this symlink for?  Is it needed as they all seem to point to the
> same thing.

The symlink is used to find the "event_source" of the "event".

/sys/devices/system/cpu/event_source/

/sys/devices/system/cpu/events/
|-- L1-dcache-load-misses
|   |-- event_source -> ../../event_source

For above example, "event_source" is the cpu pmu and the "event" is
L1-dcache-load-misses.

Yes, they point to the same thing, because all the events
under /sys/devices/system/cpu/events/* is monitored by the same event
source, ie, the cpu pmu(/sys/devices/system/cpu/event_source/).

> 
> Also, as you are trying to add new sysfs interfaces, please document
> them in Documentation/ABI.

Will add the document.

> 
> And, do you have to use "raw" kobjects here?  Any chance you can use a
> struct device instead?

Let me think about this.

> 
> I'm still not really understanding what exactly you are trying to show
> in the sysfs tree here anyway, perhaps the documentation update will
> clear that up for me.

To support multiple pmus(or call them event source), I want to show all
the pmus and events in the sysfs tree.

For cpu pmu,
/sys/devices/system/cpu/event_source/*
/sys/devices/system/cpu/events/*

For node pmu,
/sys/devices/system/node/event_source/*
/sys/devices/system/node/events/*

For mce,
/sys/kernel/events/mce/*

and so on...the exact placement is not yet final.

Thanks,
Lin Ming

> 
> thanks,
> 
> greg k-h

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