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SubjectRe: [PATCH 2/4] perf/x86/intel: fix event update for auto-reload
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.

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