| Message ID | 20200811114337.689881-1-fdmanana@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | btrfs: a few performance improvements for fsync and rename/link | expand |
On 8/11/20 7:43 AM, fdmanana@kernel.org wrote: > From: Filipe Manana <fdmanana@suse.com> > > During a rename we pin the log to make sure no one commits a log that > reflects an ongoing rename operation, as it might result in a committed > log where it recorded the unlink of the old name without having recorded > the new name. However we are taking the subvolume's log_mutex before > incrementing the log_writers counter, which is not necessary since that > counter is atomic and we only remove the old name from the log and add > the new name to the log after we have incremented log_writers, ensuring > that no one can commit the log after we have removed the old name from > the log and before we added the new name to the log. > > By taking the log_mutex lock we are just adding unnecessary contention on > the lock, which can become visible for workloads that mix renames with > fsyncs, writes for files opened with O_SYNC and unlink operations (if the > inode or its parent were fsynced before in the current transaction). > > So just remove the lock and unlock of the subvolume's log_mutex at > btrfs_pin_log_trans(). > > Using dbench, which mixes different types of operations that end up taking > that mutex (fsyncs, renames, unlinks and writes into files opened with > O_SYNC) revealed some small gains. The following script that calls dbench > was used: > > #!/bin/bash > > DEV=/dev/nvme0n1 > MNT=/mnt/btrfs > MOUNT_OPTIONS="-o ssd -o space_cache=v2" > MKFS_OPTIONS="-m single -d single" > THREADS=32 > > echo "performance" | tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor > mkfs.btrfs -f $MKFS_OPTIONS $DEV > mount $MOUNT_OPTIONS $DEV $MNT > > dbench -s -t 600 -D $MNT $THREADS > > umount $MNT > > The test was run on bare metal, no virtualization, on a box with 12 cores > (Intel i7-8700), 64Gb of RAM and using a NVMe device, with a kernel > configuration that is the default of typical distributions (debian in this > case), without debug options enabled (kasan, kmemleak, slub debug, debug > of page allocations, lock debugging, etc). > > Results before this patch: > > Operation Count AvgLat MaxLat > ---------------------------------------- > NTCreateX 4410848 0.017 738.640 > Close 3240222 0.001 0.834 > Rename 186850 7.478 1272.476 > Unlink 890875 0.128 785.018 > Deltree 128 2.846 12.081 > Mkdir 64 0.002 0.003 > Qpathinfo 3997659 0.009 11.171 > Qfileinfo 701307 0.001 0.478 > Qfsinfo 733494 0.002 1.103 > Sfileinfo 359362 0.004 3.266 > Find 1546226 0.041 4.128 > WriteX 2202803 7.905 1376.989 > ReadX 6917775 0.003 3.887 > LockX 14392 0.002 0.043 > UnlockX 14392 0.001 0.085 > Flush 309225 0.128 1033.936 > > Throughput 231.555 MB/sec (sync open) 32 clients 32 procs max_latency=1376.993 ms > > Results after this patch: > > Operation Count AvgLat MaxLat > ---------------------------------------- > NTCreateX 4603244 0.017 232.776 > Close 3381299 0.001 1.041 > Rename 194871 7.251 1073.165 > Unlink 929730 0.133 119.233 > Deltree 128 2.871 10.199 > Mkdir 64 0.002 0.004 > Qpathinfo 4171343 0.009 11.317 > Qfileinfo 731227 0.001 1.635 > Qfsinfo 765079 0.002 3.568 > Sfileinfo 374881 0.004 1.220 > Find 1612964 0.041 4.675 > WriteX 2296720 7.569 1178.204 > ReadX 7213633 0.003 3.075 > LockX 14976 0.002 0.076 > UnlockX 14976 0.001 0.061 > Flush 322635 0.102 579.505 > > Throughput 241.4 MB/sec (sync open) 32 clients 32 procs max_latency=1178.207 ms > (+4.3% throughput, -14.4% max latency) > > Signed-off-by: Filipe Manana <fdmanana@suse.com> Reviewed-by: Josef Bacik <josef@toxicpanda.com> Thanks, Josef
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c index 696dd861cc3c..4e7ef3fd5288 100644 --- a/fs/btrfs/tree-log.c +++ b/fs/btrfs/tree-log.c @@ -215,9 +215,7 @@ static int join_running_log_trans(struct btrfs_root *root) */ void btrfs_pin_log_trans(struct btrfs_root *root) { - mutex_lock(&root->log_mutex); atomic_inc(&root->log_writers); - mutex_unlock(&root->log_mutex); } /*