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>

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 6bc2500..4f9d39e 100644 (file)
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -373,6 +373,9 @@ struct hw_perf_counter {
        u64                             sample_period;
        atomic64_t                      period_left;
        u64                             interrupts;
+
+       u64                             freq_count;
+       u64                             freq_interrupts;
 #endif
 };
 

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index f839066..47c92fb 100644 (file)
--- 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);
 }