On Mon, Sep 16, 2013 at 08:07:36AM +0200, Peter Zijlstra wrote: > There already was an implicit division there, and > sizeof(pebs_record_hsw) = 176, can it really optimize that constant > division? > > I suppose we could go and introduce CONFIG_PERF_DEBUG and stuff sanity > checks under that.. :/ Or we could write it like so: --- --- a/arch/x86/kernel/cpu/perf_event_intel_ds.c +++ b/arch/x86/kernel/cpu/perf_event_intel_ds.c @@ -954,16 +954,16 @@ static void intel_pmu_drain_pebs_nhm(str ds->pebs_index = ds->pebs_buffer_base; - n = (top - at) / x86_pmu.pebs_record_size; - if (n <= 0) + if (unlikely(at > top)) return; /* * Should not happen, we program the threshold at 1 and do not * set a reset value. */ - WARN_ONCE(n > x86_pmu.max_pebs_events, - "Unexpected number of pebs records %d\n", n); + WARN_ONCE(top - at > x86_pmu.max_pebs_events * x86_pmu.pebs_record_size, + "Unexpected number of pebs records %d\n", + (top - at) / x86_pmu.pebs_record_size); for (; at < top; at += x86_pmu.pebs_record_size) { struct pebs_record_nhm *p = at; -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html