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

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Date:	Mon, 22 Mar 2010 12:43:34 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jason Baron <jbaron@...hat.com>
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, 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?

I may have missed a patch (I have not received patch 2 yet).

-- Steve

> +	}								 \
> +	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))	 \
> +	{								 \
>  		return tracepoint_probe_unregister(#name, (void *)probe);\
>  	}
>  
> @@ -86,7 +89,8 @@ struct tracepoint {
>  	__attribute__((section("__tracepoints_strings"))) = #name;	\
>  	struct tracepoint __tracepoint_##name				\
>  	__attribute__((section("__tracepoints"), aligned(32))) =	\
> -		{ __tpstrtab_##name, 0, reg, unreg, NULL }
> +		{ __tpstrtab_##name, 0, reg, unreg, NULL };		\
> +	DEFINE_JUMP_LABEL(name);
>  
>  #define DEFINE_TRACE(name)						\
>  	DEFINE_TRACE_FN(name, NULL, NULL);
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index cc89be5..8acced8 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c
> @@ -25,6 +25,7 @@
>  #include <linux/err.h>
>  #include <linux/slab.h>
>  #include <linux/sched.h>
> +#include <linux/jump_label.h>
>  
>  extern struct tracepoint __start___tracepoints[];
>  extern struct tracepoint __stop___tracepoints[];
> @@ -256,6 +257,10 @@ static void set_tracepoint(struct tracepoint_entry **entry,
>  	 * is used.
>  	 */
>  	rcu_assign_pointer(elem->funcs, (*entry)->funcs);
> +	if (!elem->state && active)
> +		enable_jump_label(elem->name);
> +	if (elem->state && !active)
> +		disable_jump_label(elem->name);
>  	elem->state = active;
>  }
>  
> @@ -270,6 +275,9 @@ static void disable_tracepoint(struct tracepoint *elem)
>  	if (elem->unregfunc && elem->state)
>  		elem->unregfunc();
>  
> +	if (elem->state)
> +		disable_jump_label(elem->name);
> +
>  	elem->state = 0;
>  	rcu_assign_pointer(elem->funcs, NULL);
>  }


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