linux-kernel - Re: [PATCH] perf: remove PERF_SAMPLE

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Message-Id: <1251363873.18584.49.camel@twins>
Date:	Thu, 27 Aug 2009 11:04:33 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Paul Mackerras <paulus@...ba.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf: remove PERF_SAMPLE_RAW

On Thu, 2009-08-27 at 10:43 +0200, Ingo Molnar wrote:
> * Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > Apparently people think trace-events became an ABI the moment perf 
> > exported them, regardless what the text surrounding 
> > PERF_SAMPLE_RAW said about the opaqueness of the data provided.
> 
> Well it's still opaque and the descriptor of what it means is in 
> debugfs so it's not an ABI as the comment says.

Clearly people their expectations didn't match this.

> > I'm not willing to make anything trace related into an ABI, hence 
> > remove this.
> 
> This removes quite a bit of nice functionality we already have, so i 
> think it's (way) too heavy handed.
> 
> I think what we want is the golden middle: a per tracepoint 
> property. I.e. we would provide:
> 
>     TRACE_EVENT_STABLE()
> 
> or TRACE_EVENT_CORE() or TRACE_EVENT_ABI() - which carries a 'will 
> maintain this as an ABI' promise from the maintainer who adds it.
> 
> Also, tracepoints are a unidirectional channel of information - in 
> practice those are way easier to handle as an ABI than other ABIs 
> such as behavior, semantics, etc. So i'd expect there to be a 
> healthy set of 'stable' tracepoints.

Whatever works for people really, I just want this discussed. I'm not at
all ready to have everything TRACE_EVENT() declared an ABI as it stands
now.
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