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

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Date:	Wed, 23 Mar 2016 11:41:29 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jiri Olsa <jolsa@...nel.org>
Cc:	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 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.

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.