On Sun, Oct 19, 2014 at 2:35 PM, Peter Zijlstra <pet...@infradead.org> wrote: > On Thu, Oct 16, 2014 at 05:00:56PM -0700, Andy Lutomirski wrote: >> The current cap_user_rdpmc code seems rather confused to me. On x86, >> *all* events set cap_user_rdpmc if the global rdpmc control is set. >> But only x86_pmu events define .event_idx, so amd uncore events won't >> actually expose their rdpmc index to userspace. >> >> Would it make more sense to add a flag PERF_X86_EVENT_RDPMC_PERMITTED >> that gets set on all events created while rdpmc == 1, to change >> x86_pmu_event_idx to do something like: >> >> if (event->hw.flags & PERF_X86_EVENT_RDPMC_PERMITTED) >> return event->hw.event_base_rdpmc + 1; >> else >> return 0; >> >> and to change arch_perf_update_userpage cap_user_rdpmc to match >> PERF_X86_EVENT_RDPMC_PERMITTED? >> >> Then we could ditch the static key and greatly simplify writes to the >> rdpmc flag by just counting PERF_X86_EVENT_RDPMC_PERMITTED events. >> >> This would be a user-visible change on AMD, and I can't test it. > > I have AMD hardware to test this. But yes something like that seems > fine.
Before I totally screw this up: is .event_idx used for anything except userspace rdpmc? There are a whole bunch of implementations of that callback: - perf_event_idx_default seems fishy - power_pmu_event_idx seems even fishier - cpumsf_pmu_event_idx is the same as power_pmu_event_idx. - perf_swevent_event_idx returns 0. etc. x86 is the only implementation of arch_perf_update_userpage, which makes me think that the .event_idx callback should just be removed and that arch_perf_update_userpage should be responsible for filling it in if needed. --Andy -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
