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

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Date:	Tue, 31 Jan 2012 16:47:56 -0800
From:	Corey Ashford <cjashfor@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Jiri Olsa <jolsa@...hat.com>, acme@...hat.com, mingo@...e.hu,
	paulus@...ba.org, linux-kernel@...r.kernel.org,
	Carl Love <carll@...ibm.com>
Subject: Re: [PATCH 5/9] perf: Adding sysfs group format attribute for pmu
 device

On 01/27/2012 01:19 PM, Peter Zijlstra wrote:
> On Fri, 2012-01-27 at 13:08 -0800, Corey Ashford wrote:
>> s an example, the IBM PowerEN processor has roughly 20 different PMU's
>> on it.  Some of those PMU's are quite complex and divide their events up
>> into subsets, each with different fields.  For example, some events may
>> have a PID matching field, and others may have an bus number matching
>> field, or matching mode field, etc.  The fields are different widths,
>> and may overlap in the config/1/2 space.
>>
>> It seems that there are two approaches you could take:
>>
>> 1) Keep your format, but allow the fields to overlap in the bit space.
>> For example:
>>
>>   "/sys/...<dev>/format/event" contains "config:0-7"
>>   "/sys/...<dev>/format/pidmatch" contains "config:8-15"
>>   "/sys/...<dev>/format/busmatch"   contains "config:8-13"
>>
>> Note that busmatch overlaps pidmatch
>>
>> 2) Create event groups that have their overlapping config space
>> separated out:
>>
>>   "/sys/...<dev>/format/event" contains "config:0-7"
>>
>>   "/sys/...<dev>.1/format/pidmatch" contains "config:8-15"
>>
>>   "/sys/...<dev>.2/format/busmatch"   contains "config:8-13"
>>
>>
>> Notice the .1 and .2 on the <dev>.
>>
>> This might help the user understand which fields go together.  I'm not
>> sold on the .1 syntax... you could do it as <dev>.<event-group-name>/ or
>> <dev>/<event-group-name>/... or whatever seems to make the most sense
>> and is relatively easy to implement and use. 
> 
> Why try and stuff those 20 in a single driver? Have 20 drivers and each
> their own format/ hierarchy.

I'm sure that could work.  Since sysfs seems to be fairly independent
(if necessary) of the hardware structure, I suppose this wouldn't be a
problem.

What do you think of Jiri's (Jirka's ?) other ideas of subdividing the
format directory?

- Corey

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