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Subject: Re: [PATCH] perf: remove PERF_SAMPLE_RAW
From: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Frederic Weisbecker <fweisbec@gmail.com>,
       Steven Rostedt <rostedt@goodmis.org>,
       Arjan van de Ven <arjan@infradead.org>,
       Paul Mackerras <paulus@samba.org>, Thomas Gleixner <tglx@linutronix.de>,
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Date: Thu, 27 Aug 2009 11:04:33 +0200
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On Thu, 2009-08-27 at 10:43 +0200, Ingo Molnar wrote:
> * Peter Zijlstra <peterz@infradead.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.