linux-kernel - Re: [PATCH 1/3] tracing: Reduce overhead of module tracepoints

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Date:	Wed, 24 Mar 2010 06:24:45 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] tracing: Reduce overhead of module tracepoints

* Li Zefan (lizf@...fujitsu.com) wrote:
> Remove the @refcnt argument, because it has side-effects, and
> arguments with side-effects are not skipped by the jump over
> disabled instrumentation, so it adds overhead even when the
> tracepoints are disabled.


Thanks Li.

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

> 
> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> ---
>  include/linux/module.h        |    6 ++----
>  include/trace/events/module.h |   14 +++++++-------
>  kernel/module.c               |    3 +--
>  3 files changed, 10 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 5e869ff..393ec39 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -460,8 +460,7 @@ static inline void __module_get(struct module *module)
>  	if (module) {
>  		preempt_disable();
>  		__this_cpu_inc(module->refptr->count);
> -		trace_module_get(module, _THIS_IP_,
> -				 __this_cpu_read(module->refptr->count));
> +		trace_module_get(module, _THIS_IP_);
>  		preempt_enable();
>  	}
>  }
> @@ -475,8 +474,7 @@ static inline int try_module_get(struct module *module)
>  
>  		if (likely(module_is_live(module))) {
>  			__this_cpu_inc(module->refptr->count);
> -			trace_module_get(module, _THIS_IP_,
> -				__this_cpu_read(module->refptr->count));
> +			trace_module_get(module, _THIS_IP_);
>  		}
>  		else
>  			ret = 0;
> diff --git a/include/trace/events/module.h b/include/trace/events/module.h
> index 4b0f48b..a585f81 100644
> --- a/include/trace/events/module.h
> +++ b/include/trace/events/module.h
> @@ -53,9 +53,9 @@ TRACE_EVENT(module_free,
>  
>  DECLARE_EVENT_CLASS(module_refcnt,
>  
> -	TP_PROTO(struct module *mod, unsigned long ip, int refcnt),
> +	TP_PROTO(struct module *mod, unsigned long ip),
>  
> -	TP_ARGS(mod, ip, refcnt),
> +	TP_ARGS(mod, ip),
>  
>  	TP_STRUCT__entry(
>  		__field(	unsigned long,	ip		)
> @@ -65,7 +65,7 @@ DECLARE_EVENT_CLASS(module_refcnt,
>  
>  	TP_fast_assign(
>  		__entry->ip	= ip;
> -		__entry->refcnt	= refcnt;
> +		__entry->refcnt	= __this_cpu_read(mod->refptr->count);
>  		__assign_str(name, mod->name);
>  	),
>  
> @@ -75,16 +75,16 @@ DECLARE_EVENT_CLASS(module_refcnt,
>  
>  DEFINE_EVENT(module_refcnt, module_get,
>  
> -	TP_PROTO(struct module *mod, unsigned long ip, int refcnt),
> +	TP_PROTO(struct module *mod, unsigned long ip),
>  
> -	TP_ARGS(mod, ip, refcnt)
> +	TP_ARGS(mod, ip)
>  );
>  
>  DEFINE_EVENT(module_refcnt, module_put,
>  
> -	TP_PROTO(struct module *mod, unsigned long ip, int refcnt),
> +	TP_PROTO(struct module *mod, unsigned long ip),
>  
> -	TP_ARGS(mod, ip, refcnt)
> +	TP_ARGS(mod, ip)
>  );
>  
>  TRACE_EVENT(module_request,
> diff --git a/kernel/module.c b/kernel/module.c
> index c968d36..21591ad 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -800,8 +800,7 @@ void module_put(struct module *module)
>  		preempt_disable();
>  		__this_cpu_dec(module->refptr->count);
>  
> -		trace_module_put(module, _RET_IP_,
> -				 __this_cpu_read(module->refptr->count));
> +		trace_module_put(module, _RET_IP_);
>  		/* Maybe they're waiting for us to drop reference? */
>  		if (unlikely(!module_is_live(module)))
>  			wake_up_process(module->waiter);
> -- 
> 1.6.3
> 

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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