ring-buffer: move code around to remove some branches
This is a bit of micro-optimizations. But since the ring buffer is used
in tracing every function call, it is an extreme hot path. Every nanosecond
counts.
This change shows over 5% improvement in the ring-buffer-benchmark.
[ Impact: more efficient code ]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index a9e645a..16b24d4 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1400,7 +1400,7 @@
unsigned long length)
{
struct ring_buffer_event *event;
- u64 ts, delta;
+ u64 ts, delta = 0;
int commit = 0;
int nr_loops = 0;
@@ -1431,20 +1431,21 @@
if (likely(cpu_buffer->tail_page == cpu_buffer->commit_page &&
rb_page_write(cpu_buffer->tail_page) ==
rb_commit_index(cpu_buffer))) {
+ u64 diff;
- delta = ts - cpu_buffer->write_stamp;
+ diff = ts - cpu_buffer->write_stamp;
- /* make sure this delta is calculated here */
+ /* make sure this diff is calculated here */
barrier();
/* Did the write stamp get updated already? */
if (unlikely(ts < cpu_buffer->write_stamp))
- delta = 0;
+ goto get_event;
- else if (unlikely(test_time_stamp(delta))) {
+ delta = diff;
+ if (unlikely(test_time_stamp(delta))) {
commit = rb_add_time_stamp(cpu_buffer, &ts, &delta);
-
if (commit == -EBUSY)
return NULL;
@@ -1453,12 +1454,11 @@
RB_WARN_ON(cpu_buffer, commit < 0);
}
- } else
- /* Non commits have zero deltas */
- delta = 0;
+ }
+ get_event:
event = __rb_reserve_next(cpu_buffer, 0, length, &ts);
- if (PTR_ERR(event) == -EAGAIN)
+ if (unlikely(PTR_ERR(event) == -EAGAIN))
goto again;
if (!event) {
