Skip to content

Commit

Permalink
ring-buffer: move code around to remove some branches
Browse files Browse the repository at this point in the history
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>
  • Loading branch information
Steven Rostedt authored and Steven Rostedt committed May 12, 2009
1 parent 88eb012 commit 168b6b1
Showing 1 changed file with 10 additions and 10 deletions.
20 changes: 10 additions & 10 deletions kernel/trace/ring_buffer.c
Original file line number Diff line number Diff line change
Expand Up @@ -1400,7 +1400,7 @@ rb_reserve_next_event(struct ring_buffer_per_cpu *cpu_buffer,
unsigned long length)
{
struct ring_buffer_event *event;
u64 ts, delta;
u64 ts, delta = 0;
int commit = 0;
int nr_loops = 0;

Expand Down Expand Up @@ -1431,20 +1431,21 @@ rb_reserve_next_event(struct ring_buffer_per_cpu *cpu_buffer,
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;

Expand All @@ -1453,12 +1454,11 @@ rb_reserve_next_event(struct ring_buffer_per_cpu *cpu_buffer,

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) {
Expand Down

0 comments on commit 168b6b1

Please sign in to comment.