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>

1 files changed, 10 insertions, 10 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index a9e645a5bc10..16b24d49604c 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -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) {