Messages in this thread | | | Date | Tue, 21 Aug 2012 15:11:36 +0200 | From | Borislav Petkov <> | Subject | Re: [RFC PATCH -v2 0/4] Persistent events |
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On Tue, Aug 21, 2012 at 12:30:50PM +0200, Peter Zijlstra wrote: > Good progress there, there's still a few things though: > > - the point also raised by Steven, I'm pretty sure that the placing of > the debugfs files unfortunate. I would much rather see something > like /debug/perf/persistent/$foo, also dropping your > perf_event_desc::dir_name.
Ok, how do we want to do the per-CPU layout there? Like this:
/debug/perf/persistent/mce_record0 /debug/perf/persistent/mce_record1 ...
or rather
/debug/perf/persistent/cpu0/mce_record /debug/perf/persistent/cpu1/mce_record
?
The thing is, I'm not sure we want to make persistent events per-CPU implicitly. If yes, then the second layout would fit better. Hmm.
> - I would make perf_add_persistent_on_cpu() static and create > something like perf_add_persistent() which iterates all CPUs and > creates: "%s-%04d", perf_event_desc::fname, cpu.
Ok.
> This needs a little extra for cpu-hotplug, not sure what to do there.
get/put_online_cpus()?
and then maybe check whether some of the CPUs are offline and warn if so?
> - related to the first point, by not tying them to actual events > you can create a persistent 'event' that contains multiple events. > Its quite possible to create multiple kernel events and use the > equivalent of PERF_EVENT_IOC_SET_OUTPUT on them to the exposed FD.
Hm, interesting.
So, in that case, the persistent thing would have a per-CPU buffer and a file descriptor connected to it and one would be able to add events which would log into the per-CPU buffer. Ok.
> - It might be good to provide means of changing the persistent > event's buffer size, or maybe even 'destroy' persistent buffers.
ioctl? Or something else?
Thanks.
-- Regards/Gruss, Boris.
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