Re: [PATCH] perf/test: Skip leader sampling for s390

[Chun-Tse Shao <ctshao@google.com>]

We believe we know the problem, appreciate Stephan Eranian's investigation.
It comes from throttling. While the sampling is too high, the generic code
does not modify event scheduling. `perf_event_overflow()` simply returns 1,
and subsequently, `pmu_stop()` only stops the leader event, not the slave
events because the arch layer does not consider groups. Also, the
`event_stop()` callback only operates on a single event, not the siblings.

This would impact all architectures. Perhaps we can extend the
`evnet_stop()` callback to include a new argument to also stop the siblings.
We also welcome all suggestions and open to discuss any potential solutions.

Thanks,
CT

Cc: Stephane Eranian <eranian@google.com>