Remove branch hints

PATCH In review David Sterba 2 participants 4 messages Oct 2, 2014 – Oct 3, 2014 Btrfs file system

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David Sterba

author

2014-10-02 16:53 UTC #0 lore raw

cover Remove branch hints

Two patches removing some 'unlikely' branch hints where it does not make much sense. Sent separately from the other cleanups in case they do not seem to fit.

You can pull from

git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux.git remove-unlikely

David Sterba (2):
btrfs: remove unlikely from NULL checks
btrfs: remove unlikely from data-dependent branches and slow paths

 fs/btrfs/async-thread.c | 10 +++++-----
 fs/btrfs/extent-tree.c  |  4 ++--
 fs/btrfs/file.c         |  4 ++--
 fs/btrfs/inode.c        | 10 +++++-----
 fs/btrfs/ioctl.c        |  2 +-
 fs/btrfs/transaction.c  |  2 +-
 6 files changed, 16 insertions(+), 16 deletions(-)

Signature · 1 line

1.8.4.5

David Sterba

author

2014-10-02 16:53 UTC #1 lore raw

PATCH 1/2 btrfs: remove unlikely from NULL checks

Unlikely is implicit for NULL checks of pointers.

Signed-off-by David Sterba <[email protected]>

---
 fs/btrfs/async-thread.c | 10 +++++-----
 fs/btrfs/inode.c        |  2 +-
 2 files changed, 6 insertions(+), 6 deletions(-)

fs/btrfs/async-thread.c +5 -5

index 2da0a66790ba..4dabeb893b7c 100644
@@ -92,7 +92,7 @@ __btrfs_alloc_workqueue(const char *name, int flags, int max_active,
 {
 	struct __btrfs_workqueue *ret = kzalloc(sizeof(*ret), GFP_NOFS);
 
-	if (unlikely(!ret))
+	if (!ret)
 		return NULL;
 
 	ret->max_active = max_active;

@@ -116,7 +116,7 @@ __btrfs_alloc_workqueue(const char *name, int flags, int max_active,
 		ret->normal_wq = alloc_workqueue("%s-%s", flags,
 						 ret->max_active, "btrfs",
 						 name);
-	if (unlikely(!ret->normal_wq)) {
+	if (!ret->normal_wq) {
 		kfree(ret);
 		return NULL;
 	}

@@ -138,12 +138,12 @@ struct btrfs_workqueue *btrfs_alloc_workqueue(const char *name,
 {
 	struct btrfs_workqueue *ret = kzalloc(sizeof(*ret), GFP_NOFS);
 
-	if (unlikely(!ret))
+	if (!ret)
 		return NULL;
 
 	ret->normal = __btrfs_alloc_workqueue(name, flags & ~WQ_HIGHPRI,
 					      max_active, thresh);
-	if (unlikely(!ret->normal)) {
+	if (!ret->normal) {
 		kfree(ret);
 		return NULL;
 	}

@@ -151,7 +151,7 @@ struct btrfs_workqueue *btrfs_alloc_workqueue(const char *name,
 	if (flags & WQ_HIGHPRI) {
 		ret->high = __btrfs_alloc_workqueue(name, flags, max_active,
 						    thresh);
-		if (unlikely(!ret->high)) {
+		if (!ret->high) {
 			__btrfs_destroy_workqueue(ret->normal);
 			kfree(ret);
 			return NULL;

fs/btrfs/inode.c +1 -1

index 344a322eb386..998e67fdf2f6 100644
@@ -9013,7 +9013,7 @@ static int __start_delalloc_inodes(struct btrfs_root *root, int delay_iput,
 		spin_unlock(&root->delalloc_lock);
 
 		work = btrfs_alloc_delalloc_work(inode, 0, delay_iput);
-		if (unlikely(!work)) {
+		if (!work) {
 			if (delay_iput)
 				btrfs_add_delayed_iput(inode);
 			else

Signature · 1 line

1.8.4.5

David Sterba

author

2014-10-02 16:53 UTC #2 lore raw

PATCH 2/2 btrfs: remove unlikely from data-dependent branches and slow paths

In reply to David Sterba

There are the branch hints that obviously depend on the data being processed, the CPU predictor will do better job according to the actual load. It also does not make sense to use the hints in slow paths that do a lot of other operations like locking, waiting or IO.

Signed-off-by David Sterba <[email protected]>

---
 fs/btrfs/extent-tree.c | 4 ++--
 fs/btrfs/file.c        | 4 ++--
 fs/btrfs/inode.c       | 8 ++++----
 fs/btrfs/ioctl.c       | 2 +-
 fs/btrfs/transaction.c | 2 +-
 5 files changed, 10 insertions(+), 10 deletions(-)

fs/btrfs/extent-tree.c +2 -2

index 44d04979f071..ede740bfaac0 100644
@@ -9694,7 +9694,7 @@ void btrfs_end_nocow_write(struct btrfs_root *root)
 
 int btrfs_start_nocow_write(struct btrfs_root *root)
 {
-	if (unlikely(atomic_read(&root->will_be_snapshoted)))
+	if (atomic_read(&root->will_be_snapshoted))
 		return 0;
 
 	percpu_counter_inc(&root->subv_writers->counter);

@@ -9702,7 +9702,7 @@ int btrfs_start_nocow_write(struct btrfs_root *root)
 	 * Make sure counter is updated before we check for snapshot creation.
 	 */
 	smp_mb();
-	if (unlikely(atomic_read(&root->will_be_snapshoted))) {
+	if (atomic_read(&root->will_be_snapshoted)) {
 		btrfs_end_nocow_write(root);
 		return 0;
 	}

fs/btrfs/file.c +2 -2

index 29b147d46b0a..a18ceabd99a8 100644
@@ -452,7 +452,7 @@ static noinline int btrfs_copy_from_user(loff_t pos, int num_pages,
 		if (unlikely(copied == 0))
 			break;
 
-		if (unlikely(copied < PAGE_CACHE_SIZE - offset)) {
+		if (copied < PAGE_CACHE_SIZE - offset) {
 			offset += copied;
 		} else {
 			pg++;

@@ -1792,7 +1792,7 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
 	if (sync)
 		atomic_inc(&BTRFS_I(inode)->sync_writers);
 
-	if (unlikely(file->f_flags & O_DIRECT)) {
+	if (file->f_flags & O_DIRECT) {
 		num_written = __btrfs_direct_write(iocb, from, pos);
 	} else {
 		num_written = __btrfs_buffered_write(file, from, pos);

fs/btrfs/inode.c +4 -4

index 998e67fdf2f6..47d214560831 100644
@@ -7802,9 +7802,9 @@ static int btrfs_submit_direct_hook(int rw, struct btrfs_dio_private *dip,
 	atomic_inc(&dip->pending_bios);
 
 	while (bvec <= (orig_bio->bi_io_vec + orig_bio->bi_vcnt - 1)) {
-		if (unlikely(map_length < submit_len + bvec->bv_len ||
+		if (map_length < submit_len + bvec->bv_len ||
 		    bio_add_page(bio, bvec->bv_page, bvec->bv_len,
-				 bvec->bv_offset) < bvec->bv_len)) {
+				 bvec->bv_offset) < bvec->bv_len) {
 			/*
 			 * inc the count before we submit the bio so
 			 * we know the end IO handler won't happen before

@@ -8017,8 +8017,8 @@ static ssize_t btrfs_direct_IO(int rw, struct kiocb *iocb,
 		ret = btrfs_delalloc_reserve_space(inode, count);
 		if (ret)
 			goto out;
-	} else if (unlikely(test_bit(BTRFS_INODE_READDIO_NEED_LOCK,
-				     &BTRFS_I(inode)->runtime_flags))) {
+	} else if (test_bit(BTRFS_INODE_READDIO_NEED_LOCK,
+				     &BTRFS_I(inode)->runtime_flags)) {
 		inode_dio_done(inode);
 		flags = DIO_LOCKING | DIO_SKIP_HOLES;
 		wakeup = false;

fs/btrfs/ioctl.c +1 -1

index 0ff212757b95..f2c60cd70e63 100644
@@ -3167,7 +3167,7 @@ static void clone_update_extent_map(struct inode *inode,
 					em->start + em->len - 1, 0);
 	}
 
-	if (unlikely(ret))
+	if (ret)
 		set_bit(BTRFS_INODE_NEEDS_FULL_SYNC,
 			&BTRFS_I(inode)->runtime_flags);
 }

fs/btrfs/transaction.c +1 -1

index 16d0c1b62b3e..8eded14e8c5c 100644
@@ -418,7 +418,7 @@ start_transaction(struct btrfs_root *root, u64 num_items, unsigned int type,
 		/*
 		 * Do the reservation for the relocation root creation
 		 */
-		if (unlikely(need_reserve_reloc_root(root))) {
+		if (need_reserve_reloc_root(root)) {
 			num_bytes += root->nodesize;
 			reloc_reserved = true;
 		}

Signature · 1 line

1.8.4.5

Zach Brown

2014-10-03 17:11 UTC #3 lore raw

In reply to David Sterba

Quoted 10 lines · David Sterba

Two patches removing some 'unlikely' branch hints where it does not make much sense. Sent separately from the other cleanups in case they do not seem to fit.
You can pull from
git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux.git remove-unlikely
David Sterba (2):
btrfs: remove unlikely from NULL checks
btrfs: remove unlikely from data-dependent branches and slow paths

Enthusiastically-Reviewed-by Zach Brown <[email protected]>

- z