linux-kernel - Re: [PATCH -tip v2 2/6] perf bts: Introduce new sub command 'perf bts trace'

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Date:	Tue, 21 Dec 2010 22:33:34 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Akihiro Nagai <akihiro.nagai.hw@...achi.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	2nddept-manager@....hitachi.co.jp,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH -tip v2 2/6] perf bts: Introduce new sub command 'perf
 bts trace'

On Tue, Dec 21, 2010 at 08:56:23PM +0100, Peter Zijlstra wrote:
> On Tue, 2010-12-21 at 20:02 +0100, Frederic Weisbecker wrote:
> 
> > This could be a PERF_SAMPLE_RAW may be?
> 
> Well clearly not ;-)
> 
> But maybe we can do something like: PERF_RECORD_SAMPLES (note the
> plural):
> 
> struct {
> 	struct perf_event_header		header;
> 
> 	u64					nr;
> 	u32					common_type;
> 	u32					data_type;
> 
> 	struct perf_sample			common;
> 	struct perf_sample			data[nr];
> }
> 
> Where struct perf_sample is PERF_RECORD_SAMPLE without the
> perf_event_header bit.
> 
> Where we can split the many samples into a piece that is the same for
> all perf_samples::common, where the content specified by the
> PERF_SAMPLE_ bits from ::common_type, and the the rest lives in data[]
> specified by the PERF_SAMPLE_ bits from ::data_type.


Well, yeah but that involves some new corner cases in both the kernel
and userspace.

What about a generic branch record like:

struct branch {
	u64 nr;
	struct {
		u64 from;
		u64 to;
	}[nr]
}

This is going to be useful also when one day we'll
support the function tracer, lbr and so...
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