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ring-buffer: move code around to remove some branches

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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>
This commit is contained in:
Steven Rostedt 2009-05-11 22:11:05 -04:00 committed by Steven Rostedt
parent 88eb012536
commit 168b6b1d05
1 changed files with 10 additions and 10 deletions
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20
kernel/trace/ring_buffer.c
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@ -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;
@ -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;
@ -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) {