perf_counter: Fix frequency adjustment for < HZ

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 25 insertions, 7 deletions

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index f8390668c391..47c92fb927f2 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -1187,8 +1187,9 @@ static void perf_log_period(struct perf_counter *counter, u64 period);
 static void perf_adjust_freq(struct perf_counter_context *ctx)
 {
         struct perf_counter *counter;
+        struct hw_perf_counter *hwc;
         u64 interrupts, sample_period;
-        u64 events, period;
+        u64 events, period, freq;
         s64 delta;
 
         spin_lock(&ctx->lock);
@@ -1196,8 +1197,10 @@ static void perf_adjust_freq(struct perf_counter_context *ctx)
                 if (counter->state != PERF_COUNTER_STATE_ACTIVE)
                         continue;
 
-                interrupts = counter->hw.interrupts;
-                counter->hw.interrupts = 0;
+                hwc = &counter->hw;
+
+                interrupts = hwc->interrupts;
+                hwc->interrupts = 0;
 
                 if (interrupts == MAX_INTERRUPTS) {
                         perf_log_throttle(counter, 1);
@@ -1208,20 +1211,35 @@ static void perf_adjust_freq(struct perf_counter_context *ctx)
                 if (!counter->attr.freq || !counter->attr.sample_freq)
                         continue;
 
-                events = HZ * interrupts * counter->hw.sample_period;
+                if (counter->attr.sample_freq < HZ) {
+                        freq = counter->attr.sample_freq;
+
+                        hwc->freq_count += freq;
+                        hwc->freq_interrupts += interrupts;
+
+                        if (hwc->freq_count < HZ)
+                                continue;
+
+                        interrupts = hwc->freq_interrupts;
+                        hwc->freq_interrupts = 0;
+                        hwc->freq_count -= HZ;
+                } else
+                        freq = HZ;
+
+                events = freq * interrupts * hwc->sample_period;
                 period = div64_u64(events, counter->attr.sample_freq);
 
-                delta = (s64)(1 + period - counter->hw.sample_period);
+                delta = (s64)(1 + period - hwc->sample_period);
                 delta >>= 1;
 
-                sample_period = counter->hw.sample_period + delta;
+                sample_period = hwc->sample_period + delta;
 
                 if (!sample_period)
                         sample_period = 1;
 
                 perf_log_period(counter, sample_period);
 
-                counter->hw.sample_period = sample_period;
+                hwc->sample_period = sample_period;
         }
         spin_unlock(&ctx->lock);
 }