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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2011-02-16 11:22:34 +0100
committerIngo Molnar <mingo@elte.hu>2011-02-16 13:30:55 +0100
commit163ec4354a5135c6c38c3f4a9b46a31900ebdf48 (patch)
tree59063e726453ace397c66d95cab09ac43265be41
parent4979d2729af22f6ce8faa325fc60a85a2c2daa02 (diff)
downloadop-kernel-dev-163ec4354a5135c6c38c3f4a9b46a31900ebdf48.zip
op-kernel-dev-163ec4354a5135c6c38c3f4a9b46a31900ebdf48.tar.gz
perf: Optimize throttling code
By pre-computing the maximum number of samples per tick we can avoid a multiplication and a conditional since MAX_INTERRUPTS > max_samples_per_tick. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu>
-rw-r--r--include/linux/perf_event.h4
-rw-r--r--kernel/perf_event.c43
-rw-r--r--kernel/sysctl.c2
3 files changed, 29 insertions, 20 deletions
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 38c8b25..8ceb5a6 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1110,6 +1110,10 @@ extern int sysctl_perf_event_paranoid;
extern int sysctl_perf_event_mlock;
extern int sysctl_perf_event_sample_rate;
+extern int perf_proc_update_handler(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp,
+ loff_t *ppos);
+
static inline bool perf_paranoid_tracepoint_raw(void)
{
return sysctl_perf_event_paranoid > -1;
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 65dcdc7..e03be08 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -150,7 +150,24 @@ int sysctl_perf_event_mlock __read_mostly = 512; /* 'free' kb per user */
/*
* max perf event sample rate
*/
-int sysctl_perf_event_sample_rate __read_mostly = 100000;
+#define DEFAULT_MAX_SAMPLE_RATE 100000
+int sysctl_perf_event_sample_rate __read_mostly = DEFAULT_MAX_SAMPLE_RATE;
+static int max_samples_per_tick __read_mostly =
+ DIV_ROUND_UP(DEFAULT_MAX_SAMPLE_RATE, HZ);
+
+int perf_proc_update_handler(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp,
+ loff_t *ppos)
+{
+ int ret = proc_dointvec(table, write, buffer, lenp, ppos);
+
+ if (ret || !write)
+ return ret;
+
+ max_samples_per_tick = DIV_ROUND_UP(sysctl_perf_event_sample_rate, HZ);
+
+ return 0;
+}
static atomic64_t perf_event_id;
@@ -4941,26 +4958,14 @@ static int __perf_event_overflow(struct perf_event *event, int nmi,
if (unlikely(!is_sampling_event(event)))
return 0;
- if (!throttle) {
- hwc->interrupts++;
- } else {
- if (hwc->interrupts != MAX_INTERRUPTS) {
- hwc->interrupts++;
- if (HZ * hwc->interrupts >
- (u64)sysctl_perf_event_sample_rate) {
- hwc->interrupts = MAX_INTERRUPTS;
- perf_log_throttle(event, 0);
- ret = 1;
- }
- } else {
- /*
- * Keep re-disabling events even though on the previous
- * pass we disabled it - just in case we raced with a
- * sched-in and the event got enabled again:
- */
+ if (unlikely(hwc->interrupts >= max_samples_per_tick)) {
+ if (throttle) {
+ hwc->interrupts = MAX_INTERRUPTS;
+ perf_log_throttle(event, 0);
ret = 1;
}
- }
+ } else
+ hwc->interrupts++;
if (event->attr.freq) {
u64 now = perf_clock();
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 0f1bd83..daef911 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -948,7 +948,7 @@ static struct ctl_table kern_table[] = {
.data = &sysctl_perf_event_sample_rate,
.maxlen = sizeof(sysctl_perf_event_sample_rate),
.mode = 0644,
- .proc_handler = proc_dointvec,
+ .proc_handler = perf_proc_update_handler,
},
#endif
#ifdef CONFIG_KMEMCHECK
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