Re: perf/ftrace: does PERF_EVENT_IOC_SET_FILTER serve any purpose?

[Ingo Molnar <mingo@kernel.org>]

* Steven Rostedt <rostedt@goodmis.org> wrote:

> On Tue, 9 Jun 2015 15:51:53 -0400 (EDT)
> Vince Weaver <vincent.weaver@maine.edu> wrote:
> 
> > On Tue, 9 Jun 2015, David Ahern wrote:
> > 
> > > On 6/9/15 12:30 PM, Vince Weaver wrote:
> > > > Hello
> > > > 
> > > > I've been working on documenting the PERF_EVENT_IOC_SET_FILTER ioctl.
> > > > 
> > > > I've been trying for the past 2 days and have been unable to get any
> > > > result except EINVAL.
> > > > 
> > > > Does anyone ever use this ioctl?  Does anyone know how to use this ioctl?
> > > 
> > > yes and yes it works.
> > > 
> > > perf record -e irq:irq_handler_entry --filter irq==28 \
> > >             -e irq:softirq_entry --filter vec==6 -a \
> > >      -- sleep 5
> > 
> > # perf record -e irq:irq_handler_entry --filter irq==28 -e irq:softirq_entry --filter vec==6 -a -- sleep 5 
> > invalid or unsupported event: 'irq:irq_handler_entry'
> > Run 'perf list' for a list of valid events
> > 
> > perf list doesn't show any tracepoint events, despite having debugfs 
> > mounted and running as root and /sys/kernel/debug/tracing/events/ being
> > populated.
> > 
> 
> What kernel are you using? You may need to update perf.
> 
> We switched to a tracefs filesystem, but the old perf wont read any events if 
> it's not located in debugfs. That is, it actually tested which filesystem the 
> event files were mounted on, and if they didn't match the debugfs mount type, it 
> ignored them. That was fixed recently.

That fix should probably be backported to stable kernels, to keep old instances 
working.

Thanks,

	Ingo