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

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Date:	Wed, 03 Mar 2010 12:07:26 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	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, 2010-03-03 at 17:37 +0100, Peter Zijlstra wrote:

> > >  	/* Trace events already protected against recursion */
> > >  	do_perf_sw_event(PERF_TYPE_TRACEPOINT, event_id, count, 1,
> > > -				&data, regs);
> > > +				&data, &regs);
> > 
> > Off-topic: Why is the above a perf sw event? Couldn't that also be a
> > normal TRACE_EVENT()?
> 
> Well, no, this is the stuff that transforms TRACE_EVENT() into perf
> software events ;-)
> 

oops, my bad :-), I thought this was in the x86 arch directory. For the
University, I was helping them with adding trace points for page faults
when I came across this in arch/x86/mm/fault.c:

	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, 0, regs, address);


This is what I actually was wondering about. Why is it a "perf only"
trace point instead of a TRACE_EVENT()?

-- Steve


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