linux-kernel - Re: [RFC][PATCH 2/3] perf: Take a hot regs snapshot for trace events

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Date:	Wed, 3 Mar 2010 21:37:09 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [RFC][PATCH 2/3] perf: Take a hot regs snapshot for trace
	events

On Wed, Mar 03, 2010 at 12:45:55PM -0500, Steven Rostedt wrote:
> On Wed, 2010-03-03 at 18:16 +0100, Peter Zijlstra wrote:
> 
> > > This is what I actually was wondering about. Why is it a "perf only"
> > > trace point instead of a TRACE_EVENT()?
> > 
> > Because I wanted to make perf usable without having to rely on funny
> > tracepoints. That is, I am less worried about committing software
> > counters to ABI than I am about TRACE_EVENT(), which still gives me a
> > terribly uncomfortable feeling.
> > 
> > Also, building with all CONFIG_TRACE_*=n will still yield a usable perf,
> > which is something the embedded people might fancy, all that TRACE stuff
> > adds lots of code.
> 
> We could make TRACE_EVENT() into a perf only trace point with
> CONFIG_TRACE_*=n. 



Yeah.


 
> Just saying that it would be nice if ftrace could also see page faults
> and such.


Agreed, we could make it a TRACE_EVENT. IIRC, someone proposed patches
for that by the past.

That notwithstanding one of the main worries is the fact TRACE_EVENT
are less ABI-stable guaranteed.

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