linux-kernel - Re: [PATCH 4/5] jump label: tracepoint support

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Date:	Mon, 22 Mar 2010 16:44:20 -0400
From:	Jason Baron <jbaron@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu,
	mathieu.desnoyers@...ymtl.ca, hpa@...or.com, tglx@...utronix.de,
	andi@...stfloor.org, roland@...hat.com, rth@...hat.com,
	mhiramat@...hat.com, fweisbec@...il.com
Subject: Re: [PATCH 4/5] jump label: tracepoint support

On Mon, Mar 22, 2010 at 12:43:34PM -0400, Steven Rostedt wrote:
> On Mon, 2010-03-22 at 12:07 -0400, Jason Baron wrote:
> > Make use of the jump label infrastructure for tracepoints.
> > 
> > Signed-off-by: Jason Baron <jbaron@...hat.com>
> > ---
> >  include/linux/tracepoint.h |   34 +++++++++++++++++++---------------
> >  kernel/tracepoint.c        |    8 ++++++++
> >  2 files changed, 27 insertions(+), 15 deletions(-)
> > 
> > diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> > index f59604e..c18b9c0 100644
> > --- a/include/linux/tracepoint.h
> > +++ b/include/linux/tracepoint.h
> > @@ -16,6 +16,7 @@
> >  
> >  #include <linux/types.h>
> >  #include <linux/rcupdate.h>
> > +#include <linux/jump_label.h>
> >  
> >  struct module;
> >  struct tracepoint;
> > @@ -63,20 +64,22 @@ struct tracepoint {
> >   * not add unwanted padding between the beginning of the section and the
> >   * structure. Force alignment to the same alignment as the section start.
> >   */
> > -#define DECLARE_TRACE(name, proto, args)				\
> > -	extern struct tracepoint __tracepoint_##name;			\
> > -	static inline void trace_##name(proto)				\
> > -	{								\
> > -		if (unlikely(__tracepoint_##name.state))		\
> > -			__DO_TRACE(&__tracepoint_##name,		\
> > -				TP_PROTO(proto), TP_ARGS(args));	\
> > -	}								\
> > -	static inline int register_trace_##name(void (*probe)(proto))	\
> > -	{								\
> > -		return tracepoint_probe_register(#name, (void *)probe);	\
> > -	}								\
> > -	static inline int unregister_trace_##name(void (*probe)(proto))	\
> > -	{								\
> > +#define DECLARE_TRACE(name, proto, args)				 \
> > +	extern struct tracepoint __tracepoint_##name;			 \
> > +	static inline void trace_##name(proto)				 \
> > +	{								 \
> > +		JUMP_LABEL(name, do_trace, __tracepoint_##name.state);   \
> > +		return;							 \
> > +do_trace:								 \
> > +		__DO_TRACE(&__tracepoint_##name,			 \
> > +			   TP_PROTO(proto), TP_ARGS(args));		 \
> 
> Does this still work on all archs, and when jump labels are not
> supported?

yes. See the base patch. If the arch doesn't have jump label support we
do:

#define JUMP_LABEL(tag, label, cond)            \
        if (unlikely(cond))                     \
                goto label;

-Jason
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