Hi Jiri, Arnaldo

Thank you for posting a patch.

Its all in tmp.perf/core, but from what I saw, yeah, he requested being
able to have a group leader.

Nakamura-san, isn't that the case?

Yes, that's right.

With these patches, I think we can use event group to register multiple 
perf events, just like PAPI.
If I find any problems, I will point them out.

Best Regards
Shunsuke