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>

1 files changed, 15 insertions, 15 deletions

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 8cf737da3ec4..1f98c78c3343 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -2916,7 +2916,7 @@ static void perf_output_get_handle(struct perf_output_handle *handle)
         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 @@ static void perf_output_put_handle(struct perf_output_handle *handle)
         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 @@ again:
          * 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 @@ int perf_output_begin(struct perf_output_handle *handle,
         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 @@ int perf_output_begin(struct perf_output_handle *handle,
                  */
                 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 @@ int perf_output_begin(struct perf_output_handle *handle,
         return 0;
 
 fail:
-        atomic_inc(&data->lost);
+        local_inc(&data->lost);
         perf_output_put_handle(handle);
 out:
         rcu_read_unlock();
@@ -3086,10 +3086,10 @@ void perf_output_end(struct perf_output_handle *handle)
         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);
                 }
         }