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Commit 61b49440 authored by Chris Mason's avatar Chris Mason
Browse files

Btrfs: Fix streaming read performance with checksumming on 



Large streaming reads make for large bios, which means each entry on the
list async work queues represents a large amount of data.  IO
congestion throttling on the device was kicking in before the async
worker threads decided a single thread was busy and needed some help.

The end result was that a streaming read would result in a single CPU
running at 100% instead of balancing the work off to other CPUs.

This patch also changes the pre-IO checksum lookup done by reads to
work on a per-bio basis instead of a per-page.  This results in many
extra btree lookups on large streaming reads.  Doing the checksum lookup
right before bio submit allows us to reuse searches while processing
adjacent offsets.

Signed-off-by: default avatarChris Mason <chris.mason@oracle.com>
parent 37d1aeee

fs/btrfs/async-thread.c

+1 −1
Original line number Diff line number Diff line
@@ -160,7 +160,7 @@ void btrfs_init_workers(struct btrfs_workers *workers, int max) 
	INIT_LIST_HEAD(&workers->idle_list);

	spin_lock_init(&workers->lock);

	workers->max_workers = max;

	workers->idle_thresh = 64;

	workers->idle_thresh = 32;

}



/*

fs/btrfs/ctree.h

+2 −0
Original line number Diff line number Diff line
@@ -1613,6 +1613,8 @@ int btrfs_lookup_inode(struct btrfs_trans_handle *trans, struct btrfs_root 
		       struct btrfs_key *location, int mod);



/* file-item.c */

int btrfs_lookup_bio_sums(struct btrfs_root *root, struct inode *inode,

			  struct bio *bio);

int btrfs_insert_file_extent(struct btrfs_trans_handle *trans,

			       struct btrfs_root *root,

			       u64 objectid, u64 pos, u64 disk_offset,

fs/btrfs/disk-io.c

+15 −0
Original line number Diff line number Diff line
@@ -1357,10 +1357,25 @@ struct btrfs_root *open_ctree(struct super_block *sb, 
	 */

	btrfs_init_workers(&fs_info->workers, fs_info->thread_pool_size);

	btrfs_init_workers(&fs_info->submit_workers, fs_info->thread_pool_size);



	/* a higher idle thresh on the submit workers makes it much more

	 * likely that bios will be send down in a sane order to the

	 * devices

	 */

	fs_info->submit_workers.idle_thresh = 64;



	btrfs_init_workers(&fs_info->fixup_workers, 1);

	btrfs_init_workers(&fs_info->endio_workers, fs_info->thread_pool_size);

	btrfs_init_workers(&fs_info->endio_write_workers,

			   fs_info->thread_pool_size);



	/*

	 * endios are largely parallel and should have a very

	 * low idle thresh

	 */

	fs_info->endio_workers.idle_thresh = 4;

	fs_info->endio_write_workers.idle_thresh = 4;



	btrfs_start_workers(&fs_info->workers, 1);

	btrfs_start_workers(&fs_info->submit_workers, 1);

	btrfs_start_workers(&fs_info->fixup_workers, 1);

fs/btrfs/file-item.c

+77 −0
Original line number Diff line number Diff line
@@ -134,6 +134,83 @@ int btrfs_lookup_file_extent(struct btrfs_trans_handle *trans, 
	return ret;

}



int btrfs_lookup_bio_sums(struct btrfs_root *root, struct inode *inode,

			  struct bio *bio)

{

	u32 sum;

	struct bio_vec *bvec = bio->bi_io_vec;

	int bio_index = 0;

	u64 offset;

	u64 item_start_offset = 0;

	u64 item_last_offset = 0;

	u32 diff;

	int ret;

	struct btrfs_path *path;

	struct btrfs_csum_item *item = NULL;

	struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;



	path = btrfs_alloc_path();

	path->reada = 2;



	WARN_ON(bio->bi_vcnt <= 0);



	while(bio_index < bio->bi_vcnt) {

		offset = page_offset(bvec->bv_page) + bvec->bv_offset;

		ret = btrfs_find_ordered_sum(inode, offset, &sum);

		if (ret == 0)

			goto found;



		if (!item || offset < item_start_offset ||

		    offset >= item_last_offset) {

			struct btrfs_key found_key;

			u32 item_size;



			if (item)

				btrfs_release_path(root, path);

			item = btrfs_lookup_csum(NULL, root, path,

						 inode->i_ino, offset, 0);

			if (IS_ERR(item)) {

				ret = PTR_ERR(item);

				if (ret == -ENOENT || ret == -EFBIG)

					ret = 0;

				sum = 0;

				printk("no csum found for inode %lu start "

				       "%llu\n", inode->i_ino,

				       (unsigned long long)offset);

				goto found;

			}

			btrfs_item_key_to_cpu(path->nodes[0], &found_key,

					      path->slots[0]);



			item_start_offset = found_key.offset;

			item_size = btrfs_item_size_nr(path->nodes[0],

						       path->slots[0]);

			item_last_offset = item_start_offset +

				(item_size / BTRFS_CRC32_SIZE) *

				root->sectorsize;

			item = btrfs_item_ptr(path->nodes[0], path->slots[0],

					      struct btrfs_csum_item);

		}

		/*

		 * this byte range must be able to fit inside

		 * a single leaf so it will also fit inside a u32

		 */

		diff = offset - item_start_offset;

		diff = diff / root->sectorsize;

		diff = diff * BTRFS_CRC32_SIZE;



		read_extent_buffer(path->nodes[0], &sum,

				   (unsigned long)item + diff,

				   BTRFS_CRC32_SIZE);

found:

		set_state_private(io_tree, offset, sum);

		bio_index++;

		bvec++;

	}

	btrfs_free_path(path);

	return 0;

}



int btrfs_csum_one_bio(struct btrfs_root *root, struct inode *inode,

		       struct bio *bio)

{

fs/btrfs/inode.c

+4 −53
Original line number Diff line number Diff line
@@ -374,6 +374,10 @@ int btrfs_submit_bio_hook(struct inode *inode, int rw, struct bio *bio, 
	BUG_ON(ret);



	if (!(rw & (1 << BIO_RW))) {

		if (!btrfs_test_opt(root, NODATASUM) &&

		    !btrfs_test_flag(inode, NODATASUM)) {

			btrfs_lookup_bio_sums(root, inode, bio);

		}

		goto mapit;

	}
@@ -598,58 +602,6 @@ int btrfs_writepage_end_io_hook(struct page *page, u64 start, u64 end, 
	return btrfs_finish_ordered_io(page->mapping->host, start, end);

}



int btrfs_readpage_io_hook(struct page *page, u64 start, u64 end)

{

	int ret = 0;

	struct inode *inode = page->mapping->host;

	struct btrfs_root *root = BTRFS_I(inode)->root;

	struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;

	struct btrfs_csum_item *item;

	struct btrfs_path *path = NULL;

	u32 csum;



	if (btrfs_test_opt(root, NODATASUM) ||

	    btrfs_test_flag(inode, NODATASUM))

		return 0;



	/*

	 * It is possible there is an ordered extent that has

	 * not yet finished for this range in the file.  If so,

	 * that extent will have a csum cached, and it will insert

	 * the sum after all the blocks in the extent are fully

	 * on disk.  So, look for an ordered extent and use the

	 * sum if found.  We have to do this before looking in the

	 * btree because csum items are pre-inserted based on

	 * the file size.  btrfs_lookup_csum might find an item

	 * that still hasn't been fully filled.

	 */

	ret = btrfs_find_ordered_sum(inode, start, &csum);

	if (ret == 0)

		goto found;



	ret = 0;

	path = btrfs_alloc_path();

	item = btrfs_lookup_csum(NULL, root, path, inode->i_ino, start, 0);

	if (IS_ERR(item)) {

		ret = PTR_ERR(item);

		/* a csum that isn't present is a preallocated region. */

		if (ret == -ENOENT || ret == -EFBIG)

			ret = 0;

		csum = 0;

		printk("no csum found for inode %lu start %Lu\n", inode->i_ino,

		       start);

		goto out;

	}

	read_extent_buffer(path->nodes[0], &csum, (unsigned long)item,

			   BTRFS_CRC32_SIZE);

found:

	set_state_private(io_tree, start, csum);

out:

	if (path)

		btrfs_free_path(path);

	return ret;

}



struct io_failure_record {

	struct page *page;

	u64 start;
@@ -3613,7 +3565,6 @@ static struct extent_io_ops btrfs_extent_io_ops = { 
	.fill_delalloc = run_delalloc_range,

	.submit_bio_hook = btrfs_submit_bio_hook,

	.merge_bio_hook = btrfs_merge_bio_hook,

	.readpage_io_hook = btrfs_readpage_io_hook,

	.readpage_end_io_hook = btrfs_readpage_end_io_hook,

	.writepage_end_io_hook = btrfs_writepage_end_io_hook,

	.writepage_start_hook = btrfs_writepage_start_hook,