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 <a...@linux-foundation.org> Cc: Christoph Hellwig <h...@lst.de> Cc: Theodore Ts'o <ty...@mit.edu> Cc: Elliott, Robert (Server Storage) <elli...@hp.com> Cc: Al Viro <v...@zeniv.linux.org.uk> Signed-off-by: Jens Axboe <ax...@fb.com> --- fs/block_dev.c | 2 +- fs/btrfs/inode.c | 6 +++--- fs/dax.c | 4 ++-- fs/direct-io.c | 7 +++++-- fs/ext4/indirect.c | 6 +++--- fs/ext4/inode.c | 4 ++-- fs/inode.c | 19 ++++++++++++++++--- fs/nfs/direct.c | 10 +++++----- include/linux/fs.h | 6 +++++- 9 files changed, 42 insertions(+), 22 deletions(-) diff --git a/fs/block_dev.c b/fs/block_dev.c index 975266be67d3..be1335dbd6be 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -155,7 +155,7 @@ blkdev_direct_IO(int rw, struct kiocb *iocb, struct iov_iter *iter, return __blockdev_direct_IO(rw, iocb, inode, I_BDEV(inode), iter, offset, blkdev_get_block, - NULL, NULL, 0); + NULL, NULL, DIO_SKIP_DIO_COUNT); } int __sync_blockdev(struct block_device *bdev, int wait) diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index d2e732d7af52..6fe341a66ed8 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -8129,7 +8129,7 @@ static ssize_t btrfs_direct_IO(int rw, struct kiocb *iocb, if (check_direct_IO(BTRFS_I(inode)->root, rw, iocb, iter, offset)) return 0; - atomic_inc(&inode->i_dio_count); + inode_dio_inc(inode); smp_mb__after_atomic(); /* @@ -8169,7 +8169,7 @@ static ssize_t btrfs_direct_IO(int rw, struct kiocb *iocb, current->journal_info = &outstanding_extents; } else if (test_bit(BTRFS_INODE_READDIO_NEED_LOCK, &BTRFS_I(inode)->runtime_flags)) { - inode_dio_done(inode); + inode_dio_dec(inode); flags = DIO_LOCKING | DIO_SKIP_HOLES; wakeup = false; } @@ -8188,7 +8188,7 @@ static ssize_t btrfs_direct_IO(int rw, struct kiocb *iocb, } out: if (wakeup) - inode_dio_done(inode); + inode_dio_dec(inode); if (relock) mutex_lock(&inode->i_mutex); diff --git a/fs/dax.c b/fs/dax.c index ed1619ec6537..1d4a9a54a938 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -210,7 +210,7 @@ ssize_t dax_do_io(int rw, struct kiocb *iocb, struct inode *inode, } /* Protects against truncate */ - atomic_inc(&inode->i_dio_count); + inode_dio_inc(inode); retval = dax_io(rw, inode, iter, pos, end, get_block, &bh); @@ -220,7 +220,7 @@ ssize_t dax_do_io(int rw, struct kiocb *iocb, struct inode *inode, if ((retval > 0) && end_io) end_io(iocb, pos, retval, bh.b_private); - inode_dio_done(inode); + inode_dio_dec(inode); out: return retval; } diff --git a/fs/direct-io.c b/fs/direct-io.c index e181b6b2e297..cba348e3135f 100644 --- a/fs/direct-io.c +++ b/fs/direct-io.c @@ -254,7 +254,9 @@ 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_dec(dio->inode); + if (is_async) { if (dio->rw & WRITE) { int err; @@ -1199,7 +1201,8 @@ do_blockdev_direct_IO(int rw, 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_inc(inode); retval = 0; sdio.blkbits = blkbits; diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c index 45fe924f82bc..bf77e5b73ae2 100644 --- a/fs/ext4/indirect.c +++ b/fs/ext4/indirect.c @@ -682,11 +682,11 @@ retry: * via ext4_inode_block_unlocked_dio(). Check inode's state * while holding extra i_dio_count ref. */ - atomic_inc(&inode->i_dio_count); + inode_dio_inc(inode); smp_mb(); if (unlikely(ext4_test_inode_state(inode, EXT4_STATE_DIOREAD_LOCK))) { - inode_dio_done(inode); + inode_dio_dec(inode); goto locked; } if (IS_DAX(inode)) @@ -696,7 +696,7 @@ retry: ret = __blockdev_direct_IO(rw, iocb, inode, inode->i_sb->s_bdev, iter, offset, ext4_get_block, NULL, NULL, 0); - inode_dio_done(inode); + inode_dio_dec(inode); } else { locked: if (IS_DAX(inode)) diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 5cb9a212b86f..62d4615aa9b0 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -2978,7 +2978,7 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb, * overwrite DIO as i_dio_count needs to be incremented under i_mutex. */ if (rw == WRITE) - atomic_inc(&inode->i_dio_count); + inode_dio_inc(inode); /* If we do a overwrite dio, i_mutex locking can be released */ overwrite = *((int *)iocb->private); @@ -3080,7 +3080,7 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb, retake_lock: if (rw == WRITE) - inode_dio_done(inode); + inode_dio_dec(inode); /* take i_mutex locking again if we do a ovewrite dio */ if (overwrite) { up_read(&EXT4_I(inode)->i_data_sem); diff --git a/fs/inode.c b/fs/inode.c index f00b16f45507..c4901c40ad65 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -1946,18 +1946,31 @@ void inode_dio_wait(struct inode *inode) EXPORT_SYMBOL(inode_dio_wait); /* - * inode_dio_done - signal finish of a direct I/O requests + * inode_dio_begin - signal start of a direct I/O requests * @inode: inode the direct I/O happens on * * This is called once we've finished processing a direct I/O request, * and is used to wake up callers waiting for direct I/O to be quiesced. */ -void inode_dio_done(struct inode *inode) +void inode_dio_inc(struct inode *inode) +{ + atomic_inc(&inode->i_dio_count); +} +EXPORT_SYMBOL(inode_dio_inc); + +/* + * inode_dio_dec - signal finish of a direct I/O requests + * @inode: inode the direct I/O happens on + * + * This is called once we've finished processing a direct I/O request, + * and is used to wake up callers waiting for direct I/O to be quiesced. + */ +void inode_dio_dec(struct inode *inode) { if (atomic_dec_and_test(&inode->i_dio_count)) wake_up_bit(&inode->i_state, __I_DIO_WAKEUP); } -EXPORT_SYMBOL(inode_dio_done); +EXPORT_SYMBOL(inode_dio_dec); /* * inode_set_flags - atomically set some inode flags diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c index e907c8cf732e..2890317173eb 100644 --- a/fs/nfs/direct.c +++ b/fs/nfs/direct.c @@ -387,7 +387,7 @@ static void nfs_direct_complete(struct nfs_direct_req *dreq, bool write) if (write) nfs_zap_mapping(inode, inode->i_mapping); - inode_dio_done(inode); + inode_dio_dec(inode); if (dreq->iocb) { long res = (long) dreq->error; @@ -487,7 +487,7 @@ static ssize_t nfs_direct_read_schedule_iovec(struct nfs_direct_req *dreq, &nfs_direct_read_completion_ops); get_dreq(dreq); desc.pg_dreq = dreq; - atomic_inc(&inode->i_dio_count); + inode_dio_inc(inode); while (iov_iter_count(iter)) { struct page **pagevec; @@ -539,7 +539,7 @@ static ssize_t nfs_direct_read_schedule_iovec(struct nfs_direct_req *dreq, * generic layer handle the completion. */ if (requested_bytes == 0) { - inode_dio_done(inode); + inode_dio_dec(inode); nfs_direct_req_release(dreq); return result < 0 ? result : -EIO; } @@ -873,7 +873,7 @@ static ssize_t nfs_direct_write_schedule_iovec(struct nfs_direct_req *dreq, &nfs_direct_write_completion_ops); desc.pg_dreq = dreq; get_dreq(dreq); - atomic_inc(&inode->i_dio_count); + inode_dio_inc(inode); NFS_I(inode)->write_io += iov_iter_count(iter); while (iov_iter_count(iter)) { @@ -929,7 +929,7 @@ static ssize_t nfs_direct_write_schedule_iovec(struct nfs_direct_req *dreq, * generic layer handle the completion. */ if (requested_bytes == 0) { - inode_dio_done(inode); + inode_dio_dec(inode); nfs_direct_req_release(dreq); return result < 0 ? result : -EIO; } diff --git a/include/linux/fs.h b/include/linux/fs.h index 52cc4492cb3a..1292ce1d9be5 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2613,6 +2613,9 @@ enum { /* filesystem can handle aio writes beyond i_size */ DIO_ASYNC_EXTEND = 0x04, + + /* inode/fs/bdev does not need truncate protection */ + DIO_SKIP_DIO_COUNT = 0x08, }; void dio_end_io(struct bio *bio, int error); @@ -2633,7 +2636,8 @@ static inline ssize_t blockdev_direct_IO(int rw, struct kiocb *iocb, #endif void inode_dio_wait(struct inode *inode); -void inode_dio_done(struct inode *inode); +void inode_dio_inc(struct inode *inode); +void inode_dio_dec(struct inode *inode); extern void inode_set_flags(struct inode *inode, unsigned int flags, unsigned int mask); -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
