linux-kernel - Re: [PATCH 1/4] tracing: move __DO

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Date:	Fri, 17 Apr 2009 12:10:05 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: Re: [PATCH 1/4] tracing: move __DO_TRACE out of line

* Ingo Molnar (mingo@...e.hu) wrote:
> 
> * Jeremy Fitzhardinge <jeremy@...p.org> wrote:
> 
> > From: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
> > 
> > Mainly simplify linux/tracepoint.h's include dependencies (removes 
> > rcupdate.h), but it can't help with icache locality, since it 
> > definitely moves the code out of line, rather than relying on gcc 
> > to do it.
> 
> > --- a/include/linux/tracepoint.h
> > +++ b/include/linux/tracepoint.h
> > @@ -15,7 +15,6 @@
> >   */
> >  
> >  #include <linux/types.h>
> > -#include <linux/rcupdate.h>
> 
> nice!
> 
> > +#define DEFINE_DO_TRACE(name, proto, args)				\
> > +	void __do_trace_##name(struct tracepoint *tp, TP_PROTO(proto))	\
> > +	{								\
> 
> that needs to be marked notrace, otherwise the function tracer 
> becomes noisy. (or even lockupy.)
> 

I guess I'll have to put it more clearly : I am all for minimizing
tracepoint header dependency, but I'll be nacking this kind of
out-of-lining patch. Taking a function call, and moving it out-of-line
(thus duplicating the function call for nothing) seems *really*
pointless and will hurt tracer performance.

If thread_info.h is now so big that it needs a cleanup, I guess we'll
just have to do it.

Mathieu

> 	Ingo

-- 
Mathieu Desnoyers
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