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Btrfs: Fix streaming read performance with checksumming on

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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: Chris Mason <chris.mason@oracle.com>
This commit is contained in:
Chris Mason
2008-07-31 15:42:53 -04:00
parent 37d1aeee39
commit 61b4944018
5 changed files with 99 additions and 54 deletions
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57
fs/btrfs/inode.c
View File

@@ -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,