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 15:08:58 -0500 |
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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. 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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