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authorLiu Bo <bo.liu@linux.alibaba.com>2018-08-22 05:54:37 +0800
committerDavid Sterba <dsterba@suse.com>2018-10-15 17:23:38 +0200
commit523983401644ebeb331c923c28c9591c07430a7d (patch)
tree242e5f93f3ed599f93882c14b8a4c420ebb26840 /fs/btrfs/delayed-inode.c
parent9b142115ed3593480b813a9331593e9f199da340 (diff)
downloadlinux-523983401644ebeb331c923c28c9591c07430a7d.tar.bz2
Btrfs: kill btrfs_clear_path_blocking
Btrfs's btree locking has two modes, spinning mode and blocking mode, while searching btree, locking is always acquired in spinning mode and then converted to blocking mode if necessary, and in some hot paths we may switch the locking back to spinning mode by btrfs_clear_path_blocking(). When acquiring locks, both of reader and writer need to wait for blocking readers and writers to complete before doing read_lock()/write_lock(). The problem is that btrfs_clear_path_blocking() needs to switch nodes in the path to blocking mode at first (by btrfs_set_path_blocking) to make lockdep happy before doing its actual clearing blocking job. When switching to blocking mode from spinning mode, it consists of step 1) bumping up blocking readers counter and step 2) read_unlock()/write_unlock(), this has caused serious ping-pong effect if there're a great amount of concurrent readers/writers, as waiters will be woken up and go to sleep immediately. 1) Killing this kind of ping-pong results in a big improvement in my 1600k files creation script, MNT=/mnt/btrfs mkfs.btrfs -f /dev/sdf mount /dev/def $MNT time fsmark -D 10000 -S0 -n 100000 -s 0 -L 1 -l /tmp/fs_log.txt \ -d $MNT/0 -d $MNT/1 \ -d $MNT/2 -d $MNT/3 \ -d $MNT/4 -d $MNT/5 \ -d $MNT/6 -d $MNT/7 \ -d $MNT/8 -d $MNT/9 \ -d $MNT/10 -d $MNT/11 \ -d $MNT/12 -d $MNT/13 \ -d $MNT/14 -d $MNT/15 w/o patch: real 2m27.307s user 0m12.839s sys 13m42.831s w/ patch: real 1m2.273s user 0m15.802s sys 8m16.495s 1.1) latency histogram from funclatency[1] Overall with the patch, there're ~50% less write lock acquisition and the 95% max latency that write lock takes also reduces to ~100ms from >500ms. -------------------------------------------- w/o patch: -------------------------------------------- Function = btrfs_tree_lock msecs : count distribution 0 -> 1 : 2385222 |****************************************| 2 -> 3 : 37147 | | 4 -> 7 : 20452 | | 8 -> 15 : 13131 | | 16 -> 31 : 3877 | | 32 -> 63 : 3900 | | 64 -> 127 : 2612 | | 128 -> 255 : 974 | | 256 -> 511 : 165 | | 512 -> 1023 : 13 | | Function = btrfs_tree_read_lock msecs : count distribution 0 -> 1 : 6743860 |****************************************| 2 -> 3 : 2146 | | 4 -> 7 : 190 | | 8 -> 15 : 38 | | 16 -> 31 : 4 | | -------------------------------------------- w/ patch: -------------------------------------------- Function = btrfs_tree_lock msecs : count distribution 0 -> 1 : 1318454 |****************************************| 2 -> 3 : 6800 | | 4 -> 7 : 3664 | | 8 -> 15 : 2145 | | 16 -> 31 : 809 | | 32 -> 63 : 219 | | 64 -> 127 : 10 | | Function = btrfs_tree_read_lock msecs : count distribution 0 -> 1 : 6854317 |****************************************| 2 -> 3 : 2383 | | 4 -> 7 : 601 | | 8 -> 15 : 92 | | 2) dbench also proves the improvement, dbench -t 120 -D /mnt/btrfs 16 w/o patch: Throughput 158.363 MB/sec w/ patch: Throughput 449.52 MB/sec 3) xfstests didn't show any additional failures. One thing to note is that callers may set path->leave_spinning to have all nodes in the path stay in spinning mode, which means callers are ready to not sleep before releasing the path, but it won't cause problems if they don't want to sleep in blocking mode. [1]: https://github.com/iovisor/bcc/blob/master/tools/funclatency.py Signed-off-by: Liu Bo <bo.liu@linux.alibaba.com> Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs/delayed-inode.c')
-rw-r--r--fs/btrfs/delayed-inode.c3
1 files changed, 0 insertions, 3 deletions
diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index 15dcbd6ef531..c669f250d4a0 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -765,9 +765,6 @@ static int btrfs_batch_insert_items(struct btrfs_root *root,
i++;
}
- /* reset all the locked nodes in the patch to spinning locks. */
- btrfs_clear_path_blocking(path, NULL, 0);
-
/* insert the keys of the items */
setup_items_for_insert(root, path, keys, data_size,
total_data_size, total_size, nitems);