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authorSteven Rostedt <srostedt@redhat.com>2010-10-08 10:50:30 -0400
committerSteven Rostedt <rostedt@goodmis.org>2010-10-20 15:17:56 -0400
commit140ff89127c74b1b1c1b0152a36ea3720ccf6bc3 (patch)
tree4948fdc850ca13b530f5b4f3c4649b2c510e1a30 /kernel
parent69d1b839f7eee347e357b3f6cce7f630cc6ff93d (diff)
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ring-buffer: Remove condition to add timestamp in fast path
There's a condition to check if we should add a time extend or not in the fast path. But this condition is racey (in the sense that we can add a unnecessary time extend, but nothing that can break anything). We later check if the time or event time delta should be zero or have real data in it (not racey), making this first check redundant. This check may help save space once in a while, but really is not worth the hassle to try to save some space that happens at most 134 ms at a time. Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/trace/ring_buffer.c28
1 files changed, 6 insertions, 22 deletions
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index f50f43107e9..d9f3e7a8213 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2119,6 +2119,7 @@ rb_reserve_next_event(struct ring_buffer *buffer,
u64 ts, delta;
int nr_loops = 0;
int add_timestamp;
+ u64 diff;
rb_start_commit(cpu_buffer);
@@ -2155,29 +2156,13 @@ rb_reserve_next_event(struct ring_buffer *buffer,
goto out_fail;
ts = rb_time_stamp(cpu_buffer->buffer);
+ diff = ts - cpu_buffer->write_stamp;
- /*
- * Only the first commit can update the timestamp.
- * Yes there is a race here. If an interrupt comes in
- * just after the conditional and it traces too, then it
- * will also check the deltas. More than one timestamp may
- * also be made. But only the entry that did the actual
- * commit will be something other than zero.
- */
- if (likely(cpu_buffer->tail_page == cpu_buffer->commit_page &&
- rb_page_write(cpu_buffer->tail_page) ==
- rb_commit_index(cpu_buffer))) {
- u64 diff;
-
- diff = ts - cpu_buffer->write_stamp;
-
- /* make sure this diff is calculated here */
- barrier();
-
- /* Did the write stamp get updated already? */
- if (unlikely(ts < cpu_buffer->write_stamp))
- goto get_event;
+ /* make sure this diff is calculated here */
+ barrier();
+ /* Did the write stamp get updated already? */
+ if (likely(ts >= cpu_buffer->write_stamp)) {
delta = diff;
if (unlikely(test_time_stamp(delta))) {
WARN_ONCE(delta > (1ULL << 59),
@@ -2189,7 +2174,6 @@ rb_reserve_next_event(struct ring_buffer *buffer,
}
}
- get_event:
event = __rb_reserve_next(cpu_buffer, length, ts,
delta, add_timestamp);
if (unlikely(PTR_ERR(event) == -EAGAIN))