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

Jiri Olsa
2016-03-24T12:25:55Z

On Thu, Mar 24, 2016 at 11:49:34AM +0100, Peter Zijlstra wrote:
> On Thu, Mar 24, 2016 at 10:56:48AM +0100, Jiri Olsa wrote:
> > 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?
>
> > > 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
>
> We're not in the business of protecting people from themselves are we?
> And if you want to help them, do so in userspace.

yep, I planned to make user space patch
to make that error more user friendly

>
> And its not like the [uk] flags are hard to implement here.

sched:sched_switch:u ?

jirka