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Commit 168b6b1d authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt
Browse files

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: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 88eb0125

kernel/trace/ring_buffer.c

+10 −10
Original line number Diff line number Diff line
@@ -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) {