[V2,2/6] Btrfs: add branch prediction hints in the read page end IO function

Commit Message

Miao Xie July 25, 2013, 11:22 a.m. UTC

This patch add some branch prediction hints into the end IO function
of the read page, it reduced the percentage of the branch misses from
5.5% to 4.9%.

Signed-off-by: Miao Xie <[e-mail]>
---
Changelog v1 -> v2:
- Just change the description in the changelog
---
 fs/btrfs/extent_io.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

Patch

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index a722235..6b6ba1a 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2502,7 +2502,7 @@  static void end_bio_extent_readpage(struct bio *bio, int err)
 
 		spin_lock(&tree->lock);
 		state = find_first_extent_bit_state(tree, start, EXTENT_LOCKED);
-		if (state && state->start == start) {
+		if (likely(state && state->start == start)) {
 			/*
 			 * take a reference on the state, unlock will drop
 			 * the ref
@@ -2512,7 +2512,8 @@  static void end_bio_extent_readpage(struct bio *bio, int err)
 		spin_unlock(&tree->lock);
 
 		mirror = io_bio->mirror_num;
-		if (uptodate && tree->ops && tree->ops->readpage_end_io_hook) {
+		if (likely(uptodate && tree->ops &&
+			   tree->ops->readpage_end_io_hook)) {
 			ret = tree->ops->readpage_end_io_hook(page, start, end,
 							      state, mirror);
 			if (ret)
@@ -2521,12 +2522,15 @@  static void end_bio_extent_readpage(struct bio *bio, int err)
 				clean_io_failure(start, page);
 		}
 
-		if (!uptodate && tree->ops && tree->ops->readpage_io_failed_hook) {
+		if (likely(uptodate))
+			goto readpage_ok;
+
+		if (tree->ops && tree->ops->readpage_io_failed_hook) {
 			ret = tree->ops->readpage_io_failed_hook(page, mirror);
 			if (!ret && !err &&
 			    test_bit(BIO_UPTODATE, &bio->bi_flags))
 				uptodate = 1;
-		} else if (!uptodate) {
+		} else {
 			/*
 			 * The generic bio_readpage_error handles errors the
 			 * following way: If possible, new read requests are
@@ -2547,7 +2551,7 @@  static void end_bio_extent_readpage(struct bio *bio, int err)
 				continue;
 			}
 		}
-
+readpage_ok:
 		if (uptodate && tree->track_uptodate) {
 			set_extent_uptodate(tree, start, end, &cached,
 					    GFP_ATOMIC);