path: root/include/trace
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authorSteven Rostedt <rostedt@goodmis.org>2013-11-14 22:57:29 -0500
committerChris Mason <chris.mason@fusionio.com>2013-11-20 20:44:47 -0500
commit4cd8587ce8fb79e49d1d6d1fc065f056188fb86a (patch)
tree3139157ec70bf16dcc5a436eccd743d41397dc5e /include/trace
parent52a157592140ac76d9f15637543aecc2100f95cb (diff)
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>
Diffstat (limited to 'include/trace')
1 files changed, 3 insertions, 1 deletions
diff --git a/include/trace/events/btrfs.h b/include/trace/events/btrfs.h
index f18b3b76e01e..4832d75dcbae 100644
--- a/include/trace/events/btrfs.h
+++ b/include/trace/events/btrfs.h
@@ -162,12 +162,14 @@ DEFINE_EVENT(btrfs__inode, btrfs_inode_evict,
TP_PROTO(struct btrfs_root *root, struct extent_map *map),
TP_ARGS(root, map),
__field( u64, root_objectid )
__field( u64, start )

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