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

[Jiri Olsa]

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.