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authorJens Axboe <axboe@fb.com>2015-04-16 02:05:48 +0300
committerAl Viro <viro@zeniv.linux.org.uk>2015-04-24 22:45:28 +0300
commitfe0f07d08ee35fb13d2cb048970072fe4f71ad14 (patch)
treebeb614e8860cfa1791143d01ba17f686304c5caf /fs/direct-io.c
parent8e3c500594dca9a12c27eb6d77b82e0766879bfd (diff)
downloadlinux-fe0f07d08ee35fb13d2cb048970072fe4f71ad14.tar.xz
direct-io: only inc/dec inode->i_dio_count for file systems
do_blockdev_direct_IO() increments and decrements the inode ->i_dio_count for each IO operation. It does this to protect against truncate of a file. Block devices don't need this sort of protection. For a capable multiqueue setup, this atomic int is the only shared state between applications accessing the device for O_DIRECT, and it presents a scaling wall for that. In my testing, as much as 30% of system time is spent incrementing and decrementing this value. A mixed read/write workload improved from ~2.5M IOPS to ~9.6M IOPS, with better latencies too. Before: clat percentiles (usec): | 1.00th=[ 33], 5.00th=[ 34], 10.00th=[ 34], 20.00th=[ 34], | 30.00th=[ 34], 40.00th=[ 34], 50.00th=[ 35], 60.00th=[ 35], | 70.00th=[ 35], 80.00th=[ 35], 90.00th=[ 37], 95.00th=[ 80], | 99.00th=[ 98], 99.50th=[ 151], 99.90th=[ 155], 99.95th=[ 155], | 99.99th=[ 165] After: clat percentiles (usec): | 1.00th=[ 95], 5.00th=[ 108], 10.00th=[ 129], 20.00th=[ 149], | 30.00th=[ 155], 40.00th=[ 161], 50.00th=[ 167], 60.00th=[ 171], | 70.00th=[ 177], 80.00th=[ 185], 90.00th=[ 201], 95.00th=[ 270], | 99.00th=[ 390], 99.50th=[ 398], 99.90th=[ 418], 99.95th=[ 422], | 99.99th=[ 438] In other setups, Robert Elliott reported seeing good performance improvements: https://lkml.org/lkml/2015/4/3/557 The more applications accessing the device, the worse it gets. Add a new direct-io flags, DIO_SKIP_DIO_COUNT, which tells do_blockdev_direct_IO() that it need not worry about incrementing or decrementing the inode i_dio_count for this caller. Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Christoph Hellwig <hch@lst.de> Cc: Theodore Ts'o <tytso@mit.edu> Cc: Elliott, Robert (Server Storage) <elliott@hp.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Jens Axboe <axboe@fb.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/direct-io.c')
-rw-r--r--fs/direct-io.c7
1 files changed, 5 insertions, 2 deletions
diff --git a/fs/direct-io.c b/fs/direct-io.c
index c3b560b24a46..745d2342651a 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -253,7 +253,9 @@ static ssize_t dio_complete(struct dio *dio, loff_t offset, ssize_t ret,
if (dio->end_io && dio->result)
dio->end_io(dio->iocb, offset, transferred, dio->private);
- inode_dio_done(dio->inode);
+ if (!(dio->flags & DIO_SKIP_DIO_COUNT))
+ inode_dio_end(dio->inode);
+
if (is_async) {
if (dio->rw & WRITE) {
int err;
@@ -1195,7 +1197,8 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
/*
* Will be decremented at I/O completion time.
*/
- atomic_inc(&inode->i_dio_count);
+ if (!(dio->flags & DIO_SKIP_DIO_COUNT))
+ inode_dio_begin(inode);
retval = 0;
sdio.blkbits = blkbits;