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Subject: Re: [RFC][PATCH v2 06/11] perf: core, export pmus via sysfs
From: Lin Ming <ming.m.lin@intel.com>
To: Greg KH <greg@kroah.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@elte.hu>,
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Date: Wed, 19 May 2010 10:34:55 +0800
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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