2012-10-26 (금), 12:23 +0200, Jiri Olsa:
> On Fri, Oct 26, 2012 at 11:14:45AM +0200, Peter Zijlstra wrote:
> > I haven't actually looked at the implementation, but I understood it to
> > be a group modifier, not an event modifier.
>
> we might want to be able to use PERF_SAMPLE_READ for single event
> same as for groups
What is the merits of doing it?
>
> the difference between single event and group 'S' modifier:
>
> $ ./perf record -e 'cycles:S' ls
> - records 'cycles' samples and read period value via PERF_SAMPLE_READ
>
> $ ./perf record -e '{cycles,cache-misses}:S'
> - samples just on 'cycles' samples and read both period values
> (cycles and cache-misses) via PERF_SAMPLE_READ group format
>
> $ ./perf record -e '{cycles,cache-misses}:S,instructions' ls
> $ ./perf record -e '{cycles:S,cache-misses},instructions' ls
> $ ./perf record -e 'cycles:S,instructions' ls
> - non matching sample_type
>
> hm, thats the unique sample_type issue again ;) Once we set
> PERF_SAMPLE_READ for event or group, we need to set it for
> all other events in session, otherwise the report fails
Sorry, I don't understand why we need to set it for all events. Just
setting it for a group is not sufficient? Please shed some light on
this.
Thanks,
Namhyung
>
> sooo, it looks like:
> - global record '-S' option instead, setting PERF_SAMPLE_READ sample type
> globaly for all events
> - and ':S' group modifier to enable sampling only on leader
> with group format reading for the rest of the group
> - ':S' group modifier alone would imply -S
>
> How about that?
>
> thanks,
> jirka
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