linux-kernel - Re: [PATCH 2/2] perf_events: add event constraints support for Intel processors

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Date:	Thu, 8 Oct 2009 22:08:39 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	David Miller <davem@...emloft.net>
Cc:	eranian@...il.com, eranian@...glemail.com, paulus@...ba.org,
	a.p.zijlstra@...llo.nl, linux-kernel@...r.kernel.org,
	perfmon2-devel@...ts.sf.net
Subject: Re: [PATCH 2/2] perf_events: add event constraints support for
	Intel processors


* David Miller <davem@...emloft.net> wrote:

> From: stephane eranian <eranian@...glemail.com>
> Date: Wed, 7 Oct 2009 14:31:58 +0200
> 
> > What PPC does is probably the only way to do this given the interface between
> > generic and machine-specific code. The one advantage I see is that it works
> > inside an event group but also across event groups because that code does not
> > look at group boundary, it only looks at the events and the number of available
> > registers. The downside is that you duplicate state.
> > 
> > Did I get this right, Paul?
> 
> That's basically how his code works, yes.  I intend on duplicating it 
> to some extent on sparc64 since I'm operating in a similar problem 
> space.
> 
> So if at least some of this engine went to a generic place, there'd be 
> at least a 3rd user :-)

Yeah, i'd definitely suggest to generalize this. We've missed updating 
PowerPC lowlevel details a couple of times in perf core updates, just 
because it's in a non-obvious place. Even if it's used by just a single 
arch, generic code is much more visible.

PowerPC really has this somewhat somewhat weird track record of 
privatizing generic facilities and smugly keeping it to themselves as a 
competitive advantage ;-) Reminds me of the old semaphore code which was 
the best on PowerPC, for years. Lets not go there again :)

	Ingo
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