linux-kernel - Re: [PATCH 1/2] tools, perf: Add a precise event qualifier v2

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Date:	Thu, 12 Sep 2013 19:59:36 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Vince Weaver <vince@...ter.net>, Andi Kleen <ak@...ux.intel.com>,
	acme@...radead.org, linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>,
	torvalds@...ux-foundation.org, trinity@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...il.com>
Subject: Re: [PATCH 1/2] tools, perf: Add a precise event qualifier v2


* Andi Kleen <andi@...stfloor.org> wrote:

> > Your feature to export 'precise' requirements on events looks useful to 
> > me. We could implement it not by special casing it implicitly but by 
> > saying that if ../format/precise contains something like:
> > 
> >    attr:240-241
> > 
> > then that's a natural extension of the config:X-Y format and should be 
> > interpreted to mean mean 2 bits in the perf attr field. I.e. we could go 
> > beyond the config bitfield.
> > 
> > Basically the whole perf_event_attr can be thought of as a 'giant 
> > bitfield', in which we can specify values to export an enumerated list of 
> > events from the kernel to tooling.
> > 
> > (Using attr:X-Y the config and config1 variants can be expressed as well, 
> > as the config fields are inside the attr structure.)
> > 
> > The positions within the perf_attr are an ABI, so this would work pretty 
> > well.
> 
> Wouldn't we need different bits for each architecture then? 32bit/64bit, 
> some archs with weird alignment rules, maybe different for BE/LE too?
> 
> Ok I suppose it could be somehow auto generated in asm-offsets.c, 
> although I'm not sure how to get a bitfield offset there.

That, or we could indeed start adding specific field names as well, which 
would have a natural position and order.

Thanks,

	Ingo
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