perf: Optimize some swcounter attr.sample_period==1 paths

Avoid the rather expensive perf_swevent_set_period() if we know
we have to sample every single event anyway.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <20091120212508.299508332@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 11 insertions, 6 deletions

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 1dfb6cc4fdea..8e55b440e28a 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -3759,16 +3759,16 @@ again:
         return nr;
 }
 
-static void perf_swevent_overflow(struct perf_event *event,
+static void perf_swevent_overflow(struct perf_event *event, u64 overflow,
                                     int nmi, struct perf_sample_data *data,
                                     struct pt_regs *regs)
 {
         struct hw_perf_event *hwc = &event->hw;
         int throttle = 0;
-        u64 overflow;
 
         data->period = event->hw.last_period;
-        overflow = perf_swevent_set_period(event);
+        if (!overflow)
+                overflow = perf_swevent_set_period(event);
 
         if (hwc->interrupts == MAX_INTERRUPTS)
                 return;
@@ -3801,14 +3801,19 @@ static void perf_swevent_add(struct perf_event *event, u64 nr,
 
         atomic64_add(nr, &event->count);
 
+        if (!regs)
+                return;
+
         if (!hwc->sample_period)
                 return;
 
-        if (!regs)
+        if (nr == 1 && hwc->sample_period == 1 && !event->attr.freq)
+                return perf_swevent_overflow(event, 1, nmi, data, regs);
+
+        if (atomic64_add_negative(nr, &hwc->period_left))
                 return;
 
-        if (!atomic64_add_negative(nr, &hwc->period_left))
-                perf_swevent_overflow(event, nmi, data, regs);
+        perf_swevent_overflow(event, 0, nmi, data, regs);
 }
 
 static int perf_swevent_is_counting(struct perf_event *event)