linux-kernel - Re: [PATCH 2/3] perf: Move exclude_kernel tracepoint check to init event

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Message-ID: <20151126194910.GA26579@krava.brq.redhat.com>
Date:	Thu, 26 Nov 2015 20:49:10 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Jiri Olsa <jolsa@...nel.org>, Steven Rostedt <rostedt@...dmis.org>,
	lkml <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 2/3] perf: Move exclude_kernel tracepoint check to init
 event

On Thu, Nov 26, 2015 at 04:41:06PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Thu, Nov 26, 2015 at 08:34:48PM +0100, Jiri Olsa escreveu:
> > We suppress events with attr::exclude_kernel set when
> > the event is generated, so following capture will
> > give no warning and produce no data:
> > 
> >   $ sudo perf record -e sched:sched_switch:u ls
> >   $ sudo /perf script | wc -l
> >   0
> > 
> > Checking the attr::exclude_kernel at the event init
> > time and failing right away:
> 
> We can as well provide a better warning in the tooling side and don't
> even ask this nonsensical combo to the kernel, right?

yep.. I'll update my todo ;-)

> 
> Arguably the kernel was doing what was asked for, its just that no
> sched:sched_switch took place while in user space... ;-)

I think it's better to fail like that.. rather than spending
time on figuring why my test did not give me any data ;-)

jirka
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