Messages in this thread | | | Subject | Re: [PATCH 2/4] perf/x86/intel: fix event update for auto-reload | From | "Liang, Kan" <> | Date | Tue, 19 Dec 2017 15:24:49 -0500 |
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On 12/19/2017 3:08 PM, Liang, Kan wrote: > > > On 12/19/2017 1:58 PM, Peter Zijlstra wrote: >> On Mon, Dec 18, 2017 at 03:34:49AM -0800, kan.liang@linux.intel.com >> wrote: >>> arch/x86/events/core.c | 14 ++++++++++++++ >>> arch/x86/events/intel/ds.c | 8 +++++++- >>> 2 files changed, 21 insertions(+), 1 deletion(-) >>> >>> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c >>> index 35552ea..f74e21d 100644 >>> --- a/arch/x86/events/core.c >>> +++ b/arch/x86/events/core.c >>> @@ -100,6 +100,20 @@ u64 x86_perf_event_update(struct perf_event *event, >>> * of the count. >>> */ >>> delta = (new_raw_count << shift) - (prev_raw_count << shift); >>> + >>> + /* >>> + * Take auto-reload into account >>> + * For the auto-reload before the last time, it went through the >>> + * whole period (reload_val) every time. >>> + * Just simply add period * times to the event. >>> + * >>> + * For the last load, the elapsed delta (event-)time need to be >>> + * corrected by adding the period. Because the start point is >>> -period. >>> + */ >>> + if (reload_times > 0) { >>> + delta += (reload_val << shift); >>> + local64_add(reload_val * (reload_times - 1), &event->count); >>> + } >>> delta >>= shift; >>> local64_add(delta, &event->count); >>> diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c >>> index 0b693b7..f0f6026 100644 >>> --- a/arch/x86/events/intel/ds.c >>> +++ b/arch/x86/events/intel/ds.c >>> @@ -1256,11 +1256,17 @@ static void __intel_pmu_pebs_event(struct >>> perf_event *event, >>> void *base, void *top, >>> int bit, int count) >>> { >>> + struct hw_perf_event *hwc = &event->hw; >>> struct perf_sample_data data; >>> struct pt_regs regs; >>> void *at = get_next_pebs_record_by_bit(base, top, bit); >>> - if (!intel_pmu_save_and_restart(event, 0, 0) && >>> + /* >>> + * Now, auto-reload is only enabled in fixed period mode. >>> + * The reload value is always hwc->sample_period. >>> + * May need to change it, if auto-reload is enabled in freq mode >>> later. >>> + */ >>> + if (!intel_pmu_save_and_restart(event, hwc->sample_period, count >>> - 1) && >>> !(event->hw.flags & PERF_X86_EVENT_AUTO_RELOAD)) >>> return; >> >> This all looks very wrong... In auto reload we should never call >> intel_pmu_save_and_restore() in the first place I think. >> >> Things like x86_perf_event_update() and x86_perf_event_set_period() >> simply _cannot_ do the right thing when we auto reload the counter. >> > > I think it should be OK to call it in first place. > For x86_perf_event_update(), the reload_times will tell if it's auto > reload. Both period_left and event->count are carefully recalculated for > auto reload.
Think a bit more. You are right. We cannot rely on count to tell us if it's auto reload. The count could also be 1 if auto reload is enabled.
I will fix it in V2.
Thanks, Kan
> For x86_perf_event_set_period(), there is nothing special needed for > auto reload. The period is fixed. The period_left from > x86_perf_event_update() is already handled. > > > BTW: It should be 'count' not 'count - 1' which pass to > intel_pmu_save_and_restart(). I just found the issue. I will fix it in > V2 with other improvements if there are any. > > Thanks, > Kan > >
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