linux-kernel - Re: [PATCH 2/7] perf: New helper function for pmu name

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Date:	Wed, 6 Oct 2010 15:18:25 +0200
From:	Robert Richter <robert.richter@....com>
To:	Paul Mundt <lethal@...ux-sh.org>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Matt Fleming <matt@...sole-pimps.org>,
	Will Deacon <will.deacon@....com>,
	Russell King <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-sh@...r.kernel.org" <linux-sh@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Deng-Cheng Zhu <dengcheng.zhu@...il.com>,
	Grant Likely <grant.likely@...retlab.ca>
Subject: Re: [PATCH 2/7] perf: New helper function for pmu name

(cc'ing Peter)

On 06.10.10 08:39:50, Paul Mundt wrote:
> On Wed, Oct 06, 2010 at 02:27:36PM +0200, Robert Richter wrote:
> > On 04.10.10 16:44:20, Matt Fleming wrote:
> > > Introduce perf_pmu_name() helper function that returns the name of the
> > > pmu. This gives us a generic way to get the name of a pmu regardless of
> > > how an architecture identifies it internally, e.g. ARM uses an id
> > > whereas SH currently uses a string.
> > 
> > I rather want use here the solution we discussed earlier, simply
> > including <asm/perf_event.h> and then access sh_pmu->name directly
> > from oprofile.
> > 
> No. Exposing sh_pmu generically is unacceptable. This is already

I don't want to be the perf_pmu_name() discussion a show stopper for
this patch set. We don't have a generic perf interface available now
that allows us to detect the pmu type for sh cpus. I also don't see a
name string as a final solution for pmu detection. So it will be more
than just adding perf_pmu_name().

Until then, as we currently would only need the name for SH, I don't
see something wrong here to include architectural interfaces from
<asm/perf_event.h> directly by architectural code until a general
solution is available.  If you run a 'git grep include..asm/perf' this
is common for other architectures.

> centrally managed through perf, and if oprofile needs any additional
> information then it needs to get that through the perf layer. We already
> have the situation that effectively every architecture with perf support
> implements a name string already, so making this part of the perf API
> hardly seems like that big of a stretch. If the perf people are violently
> opposed to this, then of course we can look at alternatives.

I am not against adding the pmu name to the perf API. But the oprofile
cpu_type strings are oprofile centric esp. for the userland. So these
strings will remain part of oprofile. Also I don't think we want to
polute the perf pmu names with it.

> sh_pmu is created for use solely by the perf events code, we are not
> going to have oprofile poking around in data structures it has no place
> knowing anything about when 99% of everything else it is doing is already
> abstracted cleanly through the perf events interfaces. Likewise for
> special oprofile-specific APIs.

So, I am also fine with implementing a generic perf_pmu_name() for sh
and then derive the oprofile cpu_type string from it in the oprofile
code.

-Robert

-- 
Advanced Micro Devices, Inc.
Operating System Research Center

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