When the inflight IOs are slow and no new IOs are issued, we expect
iostat could manifest the IO hang problem. However after
commit 5b18b5a73760 ("block: delete part_round_stats and switch to less
precise counting"), io_tick and time_in_queue will not be updated until
the end of IO, and the avgqu-sz and %util columns of iostat will be zero.

Because it has using stat.nsecs accumulation to express time_in_queue
which is not suitable to change, and may %util will express the status
better when io hang occur. To fix io_ticks, we use update_io_ticks and
inflight to update io_ticks when diskstats_show and part_stat_show
been called.

Fixes: 5b18b5a73760 ("block: delete part_round_stats and switch to less precise counting")
Signed-off-by: Zhang Wensheng <zhangwensheng5@huawei.com>
---
 block/genhd.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c
index 626c8406f21a..df0656ffb4ad 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -913,12 +913,14 @@ ssize_t part_stat_show(struct device *dev,
 	struct disk_stats stat;
 	unsigned int inflight;
 
-	part_stat_read_all(bdev, &stat);
 	if (queue_is_mq(q))
 		inflight = blk_mq_in_flight(q, bdev);
 	else
 		inflight = part_in_flight(bdev);
 
+	if (inflight)
+		update_io_ticks(bdev, jiffies, true);
+	part_stat_read_all(bdev, &stat);
 	return sprintf(buf,
 		"%8lu %8lu %8llu %8u "
 		"%8lu %8lu %8llu %8u "
@@ -1174,12 +1176,14 @@ static int diskstats_show(struct seq_file *seqf, void *v)
 	xa_for_each(&gp->part_tbl, idx, hd) {
 		if (bdev_is_partition(hd) && !bdev_nr_sectors(hd))
 			continue;
-		part_stat_read_all(hd, &stat);
 		if (queue_is_mq(gp->queue))
 			inflight = blk_mq_in_flight(gp->queue, hd);
 		else
 			inflight = part_in_flight(hd);
 
+		if (inflight)
+			update_io_ticks(hd, jiffies, true);
+		part_stat_read_all(hd, &stat);
 		seq_printf(seqf, "%4d %7d %pg "
 			   "%lu %lu %lu %u "
 			   "%lu %lu %lu %u "
-- 
2.31.1

On Tue, 25 Jan 2022 17:19:38 +0800, Zhang Wensheng wrote:
> When the inflight IOs are slow and no new IOs are issued, we expect
> iostat could manifest the IO hang problem. However after
> commit 5b18b5a73760 ("block: delete part_round_stats and switch to less
> precise counting"), io_tick and time_in_queue will not be updated until
> the end of IO, and the avgqu-sz and %util columns of iostat will be zero.
> 
> Because it has using stat.nsecs accumulation to express time_in_queue
> which is not suitable to change, and may %util will express the status
> better when io hang occur. To fix io_ticks, we use update_io_ticks and
> inflight to update io_ticks when diskstats_show and part_stat_show
> been called.
> 
> [...]

Applied, thanks!

[1/1] block: update io_ticks when io hang
      commit: 62847731488f59971413484005a7fb2772cb9249

Best regards,
-- 
Jens Axboe