metag: perf: fix frequency sampling (dynamic period)

Frequency sampling mode dynamically adjusts the sample period so as to
hit a particular frequency of samples. The sample period starts at just
1 and then gets increased if the interrupt rate is too high. This
changed sample period needs handling in metag_pmu_event_set_period to
update period_left (as the ARM equivalent does). The calculated delta
also needs subtracting from period_left in metag_pmu_event_update in
order to hit the conditional blocks in metag_pmu_event_set_period which
update last_period (which is used in the dynamic sampling period
calculation).

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>

diff --git a/arch/metag/kernel/perf/perf_event.c b/arch/metag/kernel/perf/perf_event.c
index 5bf984f..6210126 100644 (file)
--- a/arch/metag/kernel/perf/perf_event.c
+++ b/arch/metag/kernel/perf/perf_event.c
@@ -214,6 +214,7 @@ again:
        delta = (new_raw_count - prev_raw_count) & MAX_PERIOD;
 
        local64_add(delta, &event->count);
+       local64_sub(delta, &hwc->period_left);
 }
 
 int metag_pmu_event_set_period(struct perf_event *event,
@@ -223,6 +224,10 @@ int metag_pmu_event_set_period(struct perf_event *event,
        s64 period = hwc->sample_period;
        int ret = 0;
 
+       /* The period may have been changed */
+       if (unlikely(period != hwc->last_period))
+               left += period - hwc->last_period;
+
        if (unlikely(left <= -period)) {
                left = period;
                local64_set(&hwc->period_left, left);