linux-kernel - Re: [PATCH 0/3] tracing: more list_empty(perf

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Date:	Mon, 17 Jun 2013 17:27:53 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] tracing: more list_empty(perf_events) checks

On Mon, 2013-06-17 at 22:18 +0200, Oleg Nesterov wrote:
> On 06/17, Oleg Nesterov wrote:
> >
> > DECLARE_EVENT_CLASS()->perf_trace_##call() is not trivial because
> > of __perf_task()
> 
> Perhaps we can do something like below?

Did this actually compile for you?

> 
> Then we can
> 
> 	1. kill __perf_addr(), __perf_count(), __perf_task() and
> 	   TP_perf_assign()
> 
> 	2. Add the fast path check
> 
> 		if (builtin_constant(__task) && !__task &&
> 		    hlist_empty(head)))
> 			return;
> 
> 	   into perf_trace_call() right after ftrace_get_offsets_call().
> 
> Doesn't look very nice, it relies on the fact that
> ftrace_get_offsets_call(args) evaluates TP_perf_arg()'s hidden in
> TP_ARGS().
> 
> OTOH, the whole point of include/trace/ is to create the code which
> nobody except the maintainers can understand. At least I certainly
> can't ;) So perhaps this is fine.

It's the land of the MAGIC MACROs. You must be a MACRO WIZARD to
understand. I don't understand it unless I put on my MACRO WIZARD HAT.



> 
> Oleg.
> 
> --- a/include/trace/events/sched.h
> +++ b/include/trace/events/sched.h
> @@ -57,7 +57,7 @@ DECLARE_EVENT_CLASS(sched_wakeup_template,
>  
>  	TP_PROTO(struct task_struct *p, int success),
>  
> -	TP_ARGS(p, success),
> +	TP_ARGS(TP_perf_arg(__task, p), success),
>  
>  	TP_STRUCT__entry(
>  		__array(	char,	comm,	TASK_COMM_LEN	)
> @@ -73,9 +73,6 @@ DECLARE_EVENT_CLASS(sched_wakeup_template,
>  		__entry->prio		= p->prio;
>  		__entry->success	= success;
>  		__entry->target_cpu	= task_cpu(p);
> -	)
> -	TP_perf_assign(
> -		__perf_task(p);
>  	),
>  
>  	TP_printk("comm=%s pid=%d prio=%d success=%d target_cpu=%03d",
> @@ -313,7 +310,7 @@ DECLARE_EVENT_CLASS(sched_stat_template,
>  
>  	TP_PROTO(struct task_struct *tsk, u64 delay),
>  
> -	TP_ARGS(tsk, delay),
> +	TP_ARGS(TP_perf_arg(__task, tsk), TP_perf_arg(__count, delay)),
>  
>  	TP_STRUCT__entry(
>  		__array( char,	comm,	TASK_COMM_LEN	)
> @@ -325,10 +322,6 @@ DECLARE_EVENT_CLASS(sched_stat_template,
>  		memcpy(__entry->comm, tsk->comm, TASK_COMM_LEN);
>  		__entry->pid	= tsk->pid;
>  		__entry->delay	= delay;
> -	)
> -	TP_perf_assign(
> -		__perf_count(delay);
> -		__perf_task(tsk);
>  	),
>  
>  	TP_printk("comm=%s pid=%d delay=%Lu [ns]",
> --- a/include/trace/ftrace.h
> +++ b/include/trace/ftrace.h
> @@ -506,6 +506,9 @@ static inline notrace int ftrace_get_offsets_##call(			\
>  #undef TP_perf_assign
>  #define TP_perf_assign(args...)
>  
> +#undef TP_perf_arg
> +#define TP_perf_arg(var, val)	(val)
> +
>  #undef DECLARE_EVENT_CLASS
>  #define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print)	\
>  									\
> @@ -643,6 +646,9 @@ __attribute__((section("_ftrace_events"))) *__event_##call = &event_##call
>  #undef TP_perf_assign
>  #define TP_perf_assign(args...) args
>  
> +#undef TP_perf_arg
> +#define TP_perf_arg(var, val)	(var = (val))
> +
>  #undef DECLARE_EVENT_CLASS
>  #define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print)	\
>  static notrace void							\
> @@ -659,13 +665,12 @@ perf_trace_##call(void *__data, proto)					\
>  	int __data_size;						\
>  	int rctx;							\
>  									\
> -	perf_fetch_caller_regs(&__regs);				\
> -									\
>  	__data_size = ftrace_get_offsets_##call(&__data_offsets, args); \

OK, so here the task gets assigned the val, and so does count.

This may not be a bad approach, but instead of having TP_perf_arg() in
events/sched.h, keep the TP_perf_task() and TP_perf_count(), and have
whatever is put there assigned. As "__task" and "__count" are hardcoded
into the macro. The you would have:

#undef TP_perf_task
#define TP_perf_task(val) (__task = (val))

#undef TP_perf_count
#define TP_perf_count(val) (__count = (val))

And that should work as well.

-- Steve


>  	__entry_size = ALIGN(__data_size + sizeof(*entry) + sizeof(u32),\
>  			     sizeof(u64));				\
>  	__entry_size -= sizeof(u32);					\
>  									\
> +	perf_fetch_caller_regs(&__regs);				\
>  	entry = (struct ftrace_raw_##call *)perf_trace_buf_prepare(	\
>  		__entry_size, event_call->event.type, &__regs, &rctx);	\
>  	if (!entry)							\


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