[tip:perfcounters/core] perf_counter: Do not throttle single swcounter events

tip-bot for Peter Zijlstra
2009-09-17T18:07:53Z

Commit-ID: 584f7ccaaf27eb67ad137d867518db5c53286304
Gitweb: http://git.kernel.org/tip/584f7ccaaf27eb67ad137d867518db5c53286304
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Thu, 17 Sep 2009 18:47:11 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Thu, 17 Sep 2009 20:02:46 +0200

perf_counter: Do not throttle single swcounter events

We can have swcounter events that contribute more than a single
count per event, when used with a non-zero period, those can
generate multiple events, which is when we need throttling.

However, swcounter that contribute only a single count per event
can only come as fast as we can run code, hence don't throttle
them.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

---
kernel/perf_counter.c | 17 +++++++++++++----
1 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 667ab25..fe0d1ad 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -3494,14 +3494,15 @@ static void perf_log_throttle(struct perf_counter *counter, int enable)
* Generic counter overflow handling, sampling.
*/

-int perf_counter_overflow(struct perf_counter *counter, int nmi,
- struct perf_sample_data *data)
+static int __perf_counter_overflow(struct perf_counter *counter, int nmi,
+ int throttle, struct perf_sample_data *data)
{
int events = atomic_read(&counter->event_limit);
- int throttle = counter->pmu->unthrottle != NULL;
struct hw_perf_counter *hwc = &counter->hw;
int ret = 0;

+ throttle = (throttle && counter->pmu->unthrottle != NULL);
+
if (!throttle) {
hwc->interrupts++;
} else {
@@ -3554,6 +3555,12 @@ int perf_counter_overflow(struct perf_counter *counter, int nmi,
return ret;
}

+int perf_counter_overflow(struct perf_counter *counter, int nmi,
+ struct perf_sample_data *data)
+{
+ return __perf_counter_overflow(counter, nmi, 1, data);
+}
+
/*
* Generic software counter infrastructure
*/
@@ -3592,6 +3599,7 @@ static void perf_swcounter_overflow(struct perf_counter *counter,
int nmi, struct perf_sample_data *data)
{
struct hw_perf_counter *hwc = &counter->hw;
+ int throttle = 0;
u64 overflow;

data->period = counter->hw.last_period;
@@ -3601,13 +3609,14 @@ static void perf_swcounter_overflow(struct perf_counter *counter,
return;

for (; overflow; overflow--) {
- if (perf_counter_overflow(counter, nmi, data)) {
+ if (__perf_counter_overflow(counter, nmi, throttle, data)) {
/*
* We inhibit the overflow from happening when
* hwc->interrupts == MAX_INTERRUPTS.
*/
break;
}
+ throttle = 0;
}
}