Re: [PATCH v3] perf evsel: Fix missing exclude_{host,guest} setting

[Ravi Bangoria]

> The current logic for the perf missing feature has a bug that it can
> wrongly clear some modifiers like G or H.  Actually some PMUs don't
> support any filtering or exclusion while others do.  But we check it
> as a global feature.

(Sorry to pitch in bit late)

AMD has one more problem on a similar line. On AMD, non-precise and
precise sampling are provided by core and IBS pmu respectively. Plus,
core pmu has filtering capability but IBS does not. Perf by default
sets precise_ip=3 and exclude_guest=1 and goes on decreasing precise_ip
with exclude_guest set until perf_event_open() succeeds. This is
causing perf to always fallback to core pmu (non-precise mode) even if
it's perfectly feasible to do precise sampling. Do you guys think this
problem should also be addressed while designing solution for Namhyung's
patch or solve it seperately like below patch:

---><---