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

Peter Zijlstra
2016-03-23T11:01:09Z

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.