Btrfs: stop using btrfs_schedule_bio()

btrfs_schedule_bio() hands IO off to a helper thread to do the actual
submit_bio() call.  This has been used to make sure async crc and
compression helpers don't get stuck on IO submission.  To maintain good
performance, over time the IO submission threads duplicated some IO
scheduler characteristics such as high and low priority IOs and they
also made some ugly assumptions about request allocation batch sizes.

All of this cost at least one extra context switch during IO submission,
and doesn't fit well with the modern blkmq IO stack.  So, this commit stops
using btrfs_schedule_bio().  We may need to adjust the number of async
helper threads for crcs and compression, but long term it's a better
path.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

5 files changed, 15 insertions, 63 deletions

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index b05b361e2062..ae7d93bfba97 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -378,7 +378,7 @@ blk_status_t btrfs_submit_compressed_write(struct inode *inode, u64 start,
 				BUG_ON(ret); /* -ENOMEM */
 			}
 
-			ret = btrfs_map_bio(fs_info, bio, 0, 1);
+			ret = btrfs_map_bio(fs_info, bio, 0);
 			if (ret) {
 				bio->bi_status = ret;
 				bio_endio(bio);
@@ -409,7 +409,7 @@ blk_status_t btrfs_submit_compressed_write(struct inode *inode, u64 start,
 		BUG_ON(ret); /* -ENOMEM */
 	}
 
-	ret = btrfs_map_bio(fs_info, bio, 0, 1);
+	ret = btrfs_map_bio(fs_info, bio, 0);
 	if (ret) {
 		bio->bi_status = ret;
 		bio_endio(bio);
@@ -668,7 +668,7 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 						  fs_info->sectorsize);
 			sums += csum_size * nr_sectors;
 
-			ret = btrfs_map_bio(fs_info, comp_bio, mirror_num, 0);
+			ret = btrfs_map_bio(fs_info, comp_bio, mirror_num);
 			if (ret) {
 				comp_bio->bi_status = ret;
 				bio_endio(comp_bio);
@@ -693,7 +693,7 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 		BUG_ON(ret); /* -ENOMEM */
 	}
 
-	ret = btrfs_map_bio(fs_info, comp_bio, mirror_num, 0);
+	ret = btrfs_map_bio(fs_info, comp_bio, mirror_num);
 	if (ret) {
 		comp_bio->bi_status = ret;
 		bio_endio(comp_bio);
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 307861d0a040..bad83867c519 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -791,8 +791,7 @@ static void run_one_async_done(struct btrfs_work *work)
 		return;
 	}
 
-	ret = btrfs_map_bio(btrfs_sb(inode->i_sb), async->bio,
-			async->mirror_num, 1);
+	ret = btrfs_map_bio(btrfs_sb(inode->i_sb), async->bio, async->mirror_num);
 	if (ret) {
 		async->bio->bi_status = ret;
 		bio_endio(async->bio);
@@ -892,12 +891,12 @@ static blk_status_t btree_submit_bio_hook(struct inode *inode, struct bio *bio,
 					  BTRFS_WQ_ENDIO_METADATA);
 		if (ret)
 			goto out_w_error;
-		ret = btrfs_map_bio(fs_info, bio, mirror_num, 0);
+		ret = btrfs_map_bio(fs_info, bio, mirror_num);
 	} else if (!async) {
 		ret = btree_csum_one_bio(bio);
 		if (ret)
 			goto out_w_error;
-		ret = btrfs_map_bio(fs_info, bio, mirror_num, 0);
+		ret = btrfs_map_bio(fs_info, bio, mirror_num);
 	} else {
 		/*
 		 * kthread helpers are used to submit writes so that
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 2ef5f542f58a..42d1be32b2d9 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2108,7 +2108,7 @@ static blk_status_t btrfs_submit_bio_hook(struct inode *inode, struct bio *bio,
 	}
 
 mapit:
-	ret = btrfs_map_bio(fs_info, bio, mirror_num, 0);
+	ret = btrfs_map_bio(fs_info, bio, mirror_num);
 
 out:
 	if (ret) {
@@ -7850,7 +7850,7 @@ static inline blk_status_t submit_dio_repair_bio(struct inode *inode,
 	if (ret)
 		return ret;
 
-	ret = btrfs_map_bio(fs_info, bio, mirror_num, 0);
+	ret = btrfs_map_bio(fs_info, bio, mirror_num);
 
 	return ret;
 }
@@ -8376,7 +8376,7 @@ static inline blk_status_t btrfs_submit_dio_bio(struct bio *bio,
 			goto err;
 	}
 map:
-	ret = btrfs_map_bio(fs_info, bio, 0, 0);
+	ret = btrfs_map_bio(fs_info, bio, 0);
 err:
 	return ret;
 }
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index d09371b0cdf9..eb92b4bdbc64 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -6415,52 +6415,8 @@ static void btrfs_end_bio(struct bio *bio)
 	}
 }
 
-/*
- * see run_scheduled_bios for a description of why bios are collected for
- * async submit.
- *
- * This will add one bio to the pending list for a device and make sure
- * the work struct is scheduled.
- */
-static noinline void btrfs_schedule_bio(struct btrfs_device *device,
-					struct bio *bio)
-{
-	struct btrfs_fs_info *fs_info = device->fs_info;
-	int should_queue = 1;
-	struct btrfs_pending_bios *pending_bios;
-
-	/* don't bother with additional async steps for reads, right now */
-	if (bio_op(bio) == REQ_OP_READ) {
-		btrfsic_submit_bio(bio);
-		return;
-	}
-
-	WARN_ON(bio->bi_next);
-	bio->bi_next = NULL;
-
-	spin_lock(&device->io_lock);
-	if (op_is_sync(bio->bi_opf))
-		pending_bios = &device->pending_sync_bios;
-	else
-		pending_bios = &device->pending_bios;
-
-	if (pending_bios->tail)
-		pending_bios->tail->bi_next = bio;
-
-	pending_bios->tail = bio;
-	if (!pending_bios->head)
-		pending_bios->head = bio;
-	if (device->running_pending)
-		should_queue = 0;
-
-	spin_unlock(&device->io_lock);
-
-	if (should_queue)
-		btrfs_queue_work(fs_info->submit_workers, &device->work);
-}
-
 static void submit_stripe_bio(struct btrfs_bio *bbio, struct bio *bio,
-			      u64 physical, int dev_nr, int async)
+			      u64 physical, int dev_nr)
 {
 	struct btrfs_device *dev = bbio->stripes[dev_nr].dev;
 	struct btrfs_fs_info *fs_info = bbio->fs_info;
@@ -6478,10 +6434,7 @@ static void submit_stripe_bio(struct btrfs_bio *bbio, struct bio *bio,
 
 	btrfs_bio_counter_inc_noblocked(fs_info);
 
-	if (async)
-		btrfs_schedule_bio(dev, bio);
-	else
-		btrfsic_submit_bio(bio);
+	btrfsic_submit_bio(bio);
 }
 
 static void bbio_error(struct btrfs_bio *bbio, struct bio *bio, u64 logical)
@@ -6502,7 +6455,7 @@ static void bbio_error(struct btrfs_bio *bbio, struct bio *bio, u64 logical)
 }
 
 blk_status_t btrfs_map_bio(struct btrfs_fs_info *fs_info, struct bio *bio,
-			   int mirror_num, int async_submit)
+			   int mirror_num)
 {
 	struct btrfs_device *dev;
 	struct bio *first_bio = bio;
@@ -6571,7 +6524,7 @@ blk_status_t btrfs_map_bio(struct btrfs_fs_info *fs_info, struct bio *bio,
 			bio = first_bio;
 
 		submit_stripe_bio(bbio, bio, bbio->stripes[dev_nr].physical,
-				  dev_nr, async_submit);
+				  dev_nr);
 	}
 	btrfs_bio_counter_dec(fs_info);
 	return BLK_STS_OK;
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 0ae0677a8d86..bc2bbaa485b7 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -436,7 +436,7 @@ int btrfs_read_chunk_tree(struct btrfs_fs_info *fs_info);
 int btrfs_alloc_chunk(struct btrfs_trans_handle *trans, u64 type);
 void btrfs_mapping_tree_free(struct extent_map_tree *tree);
 blk_status_t btrfs_map_bio(struct btrfs_fs_info *fs_info, struct bio *bio,
-			   int mirror_num, int async_submit);
+			   int mirror_num);
 int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 		       fmode_t flags, void *holder);
 struct btrfs_device *btrfs_scan_one_device(const char *path,