Btrfs: add branch prediction hints in the read page end IO function

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 <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 5d31f80c05622a6a5d98ce4b15f6b9358694b15d..0297f6f4d4c3f34002eb4136f0955a730f5cd8e1 100644 (file)
--- 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);