linux-kernel - Re: [RFC][PATCH] perf: sysfs type id

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Date:	Tue, 09 Nov 2010 23:22:27 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Lin Ming <ming.m.lin@...el.com>,
	Stephane Eranian <eranian@...gle.com>,
	"robert.richter" <robert.richter@....com>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	fweisbec <fweisbec@...il.com>, paulus <paulus@...ba.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC][PATCH] perf: sysfs type id

On Tue, 2010-11-09 at 23:11 +0100, Kay Sievers wrote:
> On Tue, Nov 9, 2010 at 22:45, Peter Zijlstra <peterz@...radead.org> wrote:
> > The below is a RFC patch adding dynamic type ids to perf.
> >
> > We need to represent PMUs in sysfs because we want to allow multiple
> > (loadable) PMUs and need a way to identify them.
> >
> > This patch creates a new device class "pmu" and adds a single attribute
> > "type" to it. This device attribute will expose the dynamic type id as
> > required by perf_event_attr::type.
> >
> > The sysfs layout looks like:
> >
> > [root@...tmere ~]# cd /sys/class/pmu/
> 
> Please use a 'bus_type' instead of 'class'.
> 
> I'm very sure, some day, you'll need global attributes for the pmu
> stuff, and class -- unlike bus -- has its own subdir where you can go
> wild, without mixing things with the list-of-devices. :)

Having its own subdir sounds like a pro, so I'm somewhat confused. Also
the pmu (or event_source as Ingo would like it getting called) seems
like a class of devices not a bus.

USB/PCI/I2C/ISA are all buses.. pmu/event_source not so much, they are
very different (sometimes even pure software) things that provide a
common interface -- they generate events which we can count and sample.

/me dazed & confused, please do explain.

> No new stuff should use 'class', it's not extensible.

Hrm.. when I introduced the bdi stuff class was _the_ thing to use.
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