From 4cd8587ce8fb79e49d1d6d1fc065f056188fb86a Mon Sep 17 00:00:00 2001
From: Steven Rostedt <rostedt@goodmis.org>
Date: Thu, 14 Nov 2013 22:57:29 -0500
Subject: [PATCH] btrfs: Use trace condition for get_extent tracepoint
Doing an if statement to test some condition to know if we should
trigger a tracepoint is pointless when tracing is disabled. This just
adds overhead and wastes a branch prediction. This is why the
TRACE_EVENT_CONDITION() was created. It places the check inside the jump
label so that the branch does not happen unless tracing is enabled.
That is, instead of doing:
if (em)
trace_btrfs_get_extent(root, em);
Which is basically this:
if (em)
if (static_key(trace_btrfs_get_extent)) {
Using a TRACE_EVENT_CONDITION() we can just do:
trace_btrfs_get_extent(root, em);
And the condition trace event will do:
if (static_key(trace_btrfs_get_extent)) {
if (em) {
...
The static key is a non conditional jump (or nop) that is faster than
having to check if em is NULL or not.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
---
fs/btrfs/inode.c | 3 +--
include/trace/events/btrfs.h | 4 +++-
2 files changed, 4 insertions(+), 3 deletions(-)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index fd67b34e220d2..f1a77449d032b 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -6187,8 +6187,7 @@ struct extent_map *btrfs_get_extent(struct inode *inode, struct page *page,
write_unlock(&em_tree->lock);
out:
- if (em)
- trace_btrfs_get_extent(root, em);
+ trace_btrfs_get_extent(root, em);
if (path)
btrfs_free_path(path);
diff --git a/include/trace/events/btrfs.h b/include/trace/events/btrfs.h
index f18b3b76e01e2..4832d75dcbaed 100644
--- a/include/trace/events/btrfs.h
+++ b/include/trace/events/btrfs.h
@@ -162,12 +162,14 @@ DEFINE_EVENT(btrfs__inode, btrfs_inode_evict,
{ EXTENT_FLAG_LOGGING, "LOGGING" }, \
{ EXTENT_FLAG_FILLING, "FILLING" })
-TRACE_EVENT(btrfs_get_extent,
+TRACE_EVENT_CONDITION(btrfs_get_extent,
TP_PROTO(struct btrfs_root *root, struct extent_map *map),
TP_ARGS(root, map),
+ TP_CONDITION(map),
+
TP_STRUCT__entry(
__field( u64, root_objectid )
__field( u64, start )
--
GitLab