linux-kernel - Re: [PATCH 1/5] ftrace perf: Check sample types only for sampling events

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Message-ID: <20160310003637.GA21119@sejong>
Date:	Thu, 10 Mar 2016 09:36:37 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Jiri Olsa <jolsa@...nel.org>
CC:	Steven Rostedt <rostedt@...dmis.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: [PATCH 1/5] ftrace perf: Check sample types only for sampling
 events

Hi Jiri,

On Wed, Mar 09, 2016 at 09:46:41PM +0100, Jiri Olsa wrote:
> Currently we check sample type for ftrace:function event
> even if it's not created as sampling event. That prevents
> creating ftrace_function event in counting mode.
> 
> Making sure we check sample types only for sampling events.
> 
> Before:
>   $ sudo perf stat -e ftrace:function ls
>   ...
> 
>    Performance counter stats for 'ls':
> 
>      <not supported>      ftrace:function
> 
>          0.001983662 seconds time elapsed
> 
> After:
>   $ sudo perf stat -e ftrace:function ls
>   ...
> 
>    Performance counter stats for 'ls':
> 
>               44,498      ftrace:function
> 
>          0.037534722 seconds time elapsed
> 
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  kernel/trace/trace_event_perf.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
> index 00df25fd86ef..a7171ec2c1ca 100644
> --- a/kernel/trace/trace_event_perf.c
> +++ b/kernel/trace/trace_event_perf.c
> @@ -52,14 +52,14 @@ static int perf_trace_event_perm(struct trace_event_call *tp_event,
>  		 * event, due to issues with page faults while tracing page
>  		 * fault handler and its overall trickiness nature.
>  		 */
> -		if (!p_event->attr.exclude_callchain_user)
> +		if (is_sampling_event(p_event) && !p_event->attr.exclude_callchain_user)
>  			return -EINVAL;
>  
>  		/*
>  		 * Same reason to disable user stack dump as for user space
>  		 * callchains above.
>  		 */
> -		if (p_event->attr.sample_type & PERF_SAMPLE_STACK_USER)
> +		if (is_sampling_event(p_event) && p_event->attr.sample_type & PERF_SAMPLE_STACK_USER)
>  			return -EINVAL;
>  	}
>  

What about checking is_sampling_event() first and goto the last
paranoid_tracepoint_raw check instead?  This way we can remove the
same check in the function trace case.

Thanks,
Namhyung