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

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Date:	Thu, 10 Mar 2016 08:25:02 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Jiri Olsa <jolsa@...nel.org>, 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

On Thu, Mar 10, 2016 at 09:36:37AM +0900, Namhyung Kim wrote:
> 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.

right, will check

thanks,
jirka