linux-kernel - Re: [PATCH 2/5] ftrace perf: Move exclude_kernel tracepoint check to init event

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Message-ID: <20160324095648.GC8893@krava.brq.redhat.com>
Date:	Thu, 24 Mar 2016 10:56:48 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jiri Olsa <jolsa@...nel.org>, Steven Rostedt <rostedt@...dmis.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: [PATCH 2/5] ftrace perf: Move exclude_kernel tracepoint check to
 init event

On Wed, Mar 23, 2016 at 11:41:29AM +0100, Peter Zijlstra wrote:
> On Wed, Mar 16, 2016 at 03:34:30PM +0100, Jiri Olsa wrote:
> > We suppress events with attr::exclude_kernel set when
> > the event is generated, so following capture will
> > give no warning but won't produce any data:
> > 
> >   $ sudo perf record -e sched:sched_switch:u ls
> >   $ sudo /perf script | wc -l
> >   0
> > 
> > Checking the attr::exclude_(kernel|user) at the event
> > init time and failing right away for tracepoints from
> > uprobes/kprobes and native ones:
> > 
> >   $ sudo perf record -e sched:sched_switch:u ls
> >   Error:
> >   The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (sched:sched_switch).
> >   /bin/dmesg may provide additional information.
> >   No CONFIG_PERF_EVENTS=y kernel support configured?
> > 
> >   $ sudo perf record -e probe:sys_read:u ls
> >   Error:
> >   The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (probe:sys_read).
> >   /bin/dmesg may provide additional information.
> >   No CONFIG_PERF_EVENTS=y kernel support configured?
> > 
> >   $ ./perf record -e probe_ex:main:k ./ex
> >   Error:
> >   The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (probe_ex:main).
> >   /bin/dmesg may provide additional information.
> >   No CONFIG_PERF_EVENTS=y kernel support configured?
> 
> Not sure about this one. The previous behaviour suggests
> exclude_{user,kernel} is implemented, while the new behaviour says these
> flags are not implemented, which is a functional regression.

well I would not expect 'sched:sched_switch:u' to work (be implemented)

and I thought it's better to trigger an error than silently 'produce' no data

> 
> That is, if all events are from kernel space, and we exclude all kernel
> events, 0 is the right answer not an error.
> 
> Sure, with uprobes the situation is currently broken, but this isn't a
> fix.