perf: Optimize the hotpath by converting the perf output buffer to local_t
Since there is now only a single writer, we can use
local_t instead and avoid all these pesky LOCK insn.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 8cf737d..1f98c78 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -2916,7 +2916,7 @@
struct perf_mmap_data *data = handle->data;
preempt_disable();
- atomic_inc(&data->nest);
+ local_inc(&data->nest);
}
static void perf_output_put_handle(struct perf_output_handle *handle)
@@ -2925,13 +2925,13 @@
unsigned long head;
again:
- head = atomic_long_read(&data->head);
+ head = local_read(&data->head);
/*
* IRQ/NMI can happen here, which means we can miss a head update.
*/
- if (!atomic_dec_and_test(&data->nest))
+ if (!local_dec_and_test(&data->nest))
return;
/*
@@ -2945,12 +2945,12 @@
* Now check if we missed an update, rely on the (compiler)
* barrier in atomic_dec_and_test() to re-read data->head.
*/
- if (unlikely(head != atomic_long_read(&data->head))) {
- atomic_inc(&data->nest);
+ if (unlikely(head != local_read(&data->head))) {
+ local_inc(&data->nest);
goto again;
}
- if (atomic_xchg(&data->wakeup, 0))
+ if (local_xchg(&data->wakeup, 0))
perf_output_wakeup(handle);
preempt_enable();
@@ -3031,7 +3031,7 @@
if (!data->nr_pages)
goto out;
- have_lost = atomic_read(&data->lost);
+ have_lost = local_read(&data->lost);
if (have_lost)
size += sizeof(lost_event);
@@ -3045,24 +3045,24 @@
*/
tail = ACCESS_ONCE(data->user_page->data_tail);
smp_rmb();
- offset = head = atomic_long_read(&data->head);
+ offset = head = local_read(&data->head);
head += size;
if (unlikely(!perf_output_space(data, tail, offset, head)))
goto fail;
- } while (atomic_long_cmpxchg(&data->head, offset, head) != offset);
+ } while (local_cmpxchg(&data->head, offset, head) != offset);
handle->offset = offset;
handle->head = head;
if (head - tail > data->watermark)
- atomic_inc(&data->wakeup);
+ local_inc(&data->wakeup);
if (have_lost) {
lost_event.header.type = PERF_RECORD_LOST;
lost_event.header.misc = 0;
lost_event.header.size = sizeof(lost_event);
lost_event.id = event->id;
- lost_event.lost = atomic_xchg(&data->lost, 0);
+ lost_event.lost = local_xchg(&data->lost, 0);
perf_output_put(handle, lost_event);
}
@@ -3070,7 +3070,7 @@
return 0;
fail:
- atomic_inc(&data->lost);
+ local_inc(&data->lost);
perf_output_put_handle(handle);
out:
rcu_read_unlock();
@@ -3086,10 +3086,10 @@
int wakeup_events = event->attr.wakeup_events;
if (handle->sample && wakeup_events) {
- int events = atomic_inc_return(&data->events);
+ int events = local_inc_return(&data->events);
if (events >= wakeup_events) {
- atomic_sub(wakeup_events, &data->events);
- atomic_inc(&data->wakeup);
+ local_sub(wakeup_events, &data->events);
+ local_inc(&data->wakeup);
}
}