From fe0f07d08ee35fb13d2cb048970072fe4f71ad14 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Wed, 15 Apr 2015 17:05:48 -0600 Subject: 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 Cc: Christoph Hellwig Cc: Theodore Ts'o Cc: Elliott, Robert (Server Storage) Cc: Al Viro Signed-off-by: Jens Axboe Signed-off-by: Al Viro --- fs/nfs/direct.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) (limited to 'fs/nfs/direct.c') diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c index ed0e6031be88..b2cbc3a6cdd9 100644 --- a/fs/nfs/direct.c +++ b/fs/nfs/direct.c @@ -386,7 +386,7 @@ 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_end(inode); if (dreq->iocb) { long res = (long) dreq->error; @@ -486,7 +486,7 @@ 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_begin(inode); while (iov_iter_count(iter)) { struct page **pagevec; @@ -538,7 +538,7 @@ 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_end(inode); nfs_direct_req_release(dreq); return result < 0 ? result : -EIO; } @@ -872,7 +872,7 @@ 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_begin(inode); NFS_I(inode)->write_io += iov_iter_count(iter); while (iov_iter_count(iter)) { @@ -928,7 +928,7 @@ 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_end(inode); nfs_direct_req_release(dreq); return result < 0 ? result : -EIO; } -- cgit v1.2.3