[tip:perfcounters/core] perf_counter: Fix frequency adjustment for < HZ

tip-bot for Peter Zijlstra
2009-06-05T16:58:50Z

Commit-ID: 6a24ed6c6082ec65d19331a4bfa30c0512a1a822
Gitweb: http://git.kernel.org/tip/6a24ed6c6082ec65d19331a4bfa30c0512a1a822
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Fri, 5 Jun 2009 18:01:29 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Fri, 5 Jun 2009 18:07:48 +0200

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>

---
include/linux/perf_counter.h | 3 +++
kernel/perf_counter.c | 32 +++++++++++++++++++++++++-------
2 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 6bc2500..4f9d39e 100644
--- 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
--- 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);
}