linux-kernel - Re: [lkp-robot] [fs] 91f9943e1c: aim7.jobs-per-min -26.6% regression

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Date:   Mon, 16 Oct 2017 09:34:18 +0200
From:   Christoph Hellwig <hch@....de>
To:     kernel test robot <xiaolong.ye@...el.com>
Cc:     Christoph Hellwig <hch@....de>, Al Viro <viro@...iv.linux.org.uk>,
        Jan Kara <jack@...e.cz>, LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>, lkp@...org
Subject: Re: [lkp-robot] [fs]  91f9943e1c:  aim7.jobs-per-min -26.6%
        regression

The only change for the non-nowait case is that we now do a trylock before
locking i_rwsem.  In the past that was the more optimal pattern.  Can you
test the patch below if that's not the case anymore?  We have a few more
instances like that which might also want to be changed then.

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 309e26c9dddb..ad61c78605d1 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -258,10 +258,11 @@ xfs_file_buffered_aio_read(
 	ssize_t			ret;
 
 	trace_xfs_file_buffered_read(ip, iov_iter_count(to), iocb->ki_pos);
-
-	if (!xfs_ilock_nowait(ip, XFS_IOLOCK_SHARED)) {
-		if (iocb->ki_flags & IOCB_NOWAIT)
+		
+	if (iocb->ki_flags & IOCB_NOWAIT) {
+		if (!xfs_ilock_nowait(ip, XFS_IOLOCK_SHARED))
 			return -EAGAIN;
+	} else {
 		xfs_ilock(ip, XFS_IOLOCK_SHARED);
 	}
 	ret = generic_file_read_iter(iocb, to);