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

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Date:	Thu, 8 Oct 2009 22:28:29 +0200
From:	stephane eranian <eranian@...glemail.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	David Miller <davem@...emloft.net>, 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

On Thu, Oct 8, 2009 at 10:08 PM, Ingo Molnar <mingo@...e.hu> wrote:
>
> * 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.
>

It is not clear how you can do this without creating a monster.
As I said the constraints can be far more difficult than just
event X => allowed_counter_bitmask.
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