xfs: increase the default parallelism levels of pwork clientspwork-parallelism_2019-11-22

Increase the default parallelism level for pwork clients so that we can
take advantage of computers with a lot of CPUs and a lot of hardware.

8x raid0 spinning rust running quotacheck:
1		39s
2		29s
4		26s
8		24s
24 (nr_cpus)	24s

4x raid0 sata ssds running quotacheck:
1		12s
2		12s
4		12s
8		13s
24 (nr_cpus)	14s

4x raid0 nvme ssds running quotacheck:
1		18s
2		18s
4		19s
8		20s
20 (nr_cpus)	20s

So, mixed results...

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

1 files changed, 38 insertions, 3 deletions

diff --git a/fs/xfs/xfs_pwork.c b/fs/xfs/xfs_pwork.c
index 4bcc3e61056c..9589995a5137 100644
--- a/fs/xfs/xfs_pwork.c
+++ b/fs/xfs/xfs_pwork.c
@@ -127,10 +127,45 @@ xfs_pwork_guess_datadev_parallelism(
 	struct xfs_mount	*mp)
 {
 	struct xfs_buftarg	*btp = mp->m_ddev_targp;
+	unsigned int		threads;
+	unsigned int		max_threads;
+	int			iomin;
+	int			ioopt;
 
 	/*
-	 * For now we'll go with the most conservative setting possible,
-	 * which is two threads for an SSD and 1 thread everywhere else.
+	 * For metadata activities we probably can't scale further than the
+	 * number of AGs and the number of online CPUs; and we must abide the
+	 * workqueue maximum thread count.
 	 */
-	return blk_queue_nonrot(btp->bt_bdev->bd_queue) ? 2 : 1;
+	max_threads = min(mp->m_sb.sb_agcount,
+			min_t(unsigned int, num_online_cpus(), WQ_MAX_ACTIVE));
+
+	if (blk_queue_nonrot(btp->bt_bdev->bd_queue)) {
+		threads = max_threads;
+		goto out;
+	}
+
+	/*
+	 * For filesystems on rotational storage with configured stripe width
+	 * and stripe units, we assume that there's a multidisk setup (e.g.
+	 * RAID) and that we can parallelise according to the setup's geometry.
+	 * First we try the values in the superblock and then we resort to
+	 * probing the block layer.
+	 */
+	if (mp->m_sb.sb_width && mp->m_sb.sb_unit) {
+		threads = mp->m_sb.sb_width / mp->m_sb.sb_unit;
+		goto out;
+	}
+
+	iomin = bdev_io_min(btp->bt_bdev);
+	ioopt = bdev_io_opt(btp->bt_bdev);
+	if (iomin > 0 && ioopt > 0) {
+		threads = ioopt / iomin;
+		goto out;
+	}
+
+	/* Unexciting rotating disks get one thread. */
+	threads = 1;
+out:
+	return clamp(threads, 1U, max_threads);
 }