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Subject: Re: [PATCH] tracing, perf: add more power related events
From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>,
        Jean Pihet <jean.pihet@newoldbits.com>,
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Date: Wed, 22 Sep 2010 20:26:40 +0200
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On Wed, 2010-09-22 at 14:15 -0400, Steven Rostedt wrote:
> On Wed, 2010-09-22 at 19:30 +0200, Peter Zijlstra wrote:
> > On Wed, 2010-09-22 at 10:06 -0700, Arjan van de Ven wrote:
> > 
> 
> > That said, I really didn't read this discussion much, but your stance
> > seems to be that any tracepoint you use must stay valid, and I object to
> > that.
> 
> We could add a TRACE_EVENT_ABI() as Ingo has been suggesting. If
> anything, it could mean that the given tracepoint will always have the
> same name. And perhaps the data it holds will always be there, but may
> also be extended.

I still don't see why you need TRACE_EVENT_ABI for that, if its the same
name and the format can be extended you get the same results with what
we've got. Apps need to read/parse the format thing anyway.

> > 
> > What will do you do when we include a new scheduling policy and all the
> > scheduler tracepoints need to change? (yes that's really going to
> > happen)
> 
> The tracepoint sched_switch should stay the same. We may add more data,
> but the comm, pid, prio => comm, pid, prio, I don't see going away.

Right, it would need additional fields. Preferably not only at the end.

> > I'm not going to carry double tracepoints, and I'm not going to not
> > merge that policy. 
> 
> Not sure what you mean by "double tracepoints"

Two different tracepoints in the same location.