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Subject: Re: [RFC][PATCH 2/3] perf: Take a hot regs snapshot for trace
 events
From: Peter Zijlstra <peterz@infradead.org>
To: rostedt@goodmis.org
Cc: Frederic Weisbecker <fweisbec@gmail.com>, Ingo Molnar <mingo@elte.hu>,
       LKML <linux-kernel@vger.kernel.org>,
       Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
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       Arnaldo Carvalho de Melo <acme@redhat.com>
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Date: Wed, 03 Mar 2010 17:37:38 +0100
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On Wed, 2010-03-03 at 11:06 -0500, Steven Rostedt wrote:
> On Wed, 2010-03-03 at 07:55 +0100, Frederic Weisbecker wrote:
> 
> > +/*
> >   * Output
> >   */
> >  static bool perf_output_space(struct perf_mmap_data *data, unsigned long tail,
> > @@ -4337,6 +4347,8 @@ static const struct pmu perf_ops_task_clock = {
> >  void perf_tp_event(int event_id, u64 addr, u64 count, void *record,
> >  			  int entry_size)
> >  {
> > +	struct pt_regs regs;
> > +
> >  	struct perf_raw_record raw = {
> >  		.size = entry_size,
> >  		.data = record,
> > @@ -4347,14 +4359,11 @@ void perf_tp_event(int event_id, u64 addr, u64 count, void *record,
> >  		.raw = &raw,
> >  	};
> >  
> > -	struct pt_regs *regs = get_irq_regs();
> > -
> > -	if (!regs)
> > -		regs = task_pt_regs(current);
> > +	PERF_SAVE_REGS(&regs);
> >  
> >  	/* 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 ;-)