block: fix that util can be greater than 100%

util means the percentage that disk has IO, and theoretically it should
not be greater than 100%. However, there is a gap for rq-based disk:

io_ticks will be updated when rq is allocated, however, before such rq
dispatch to driver, it will not be account as inflight from
blk_mq_start_request() hence diskstats_show()/part_stat_show() will not
update io_ticks. For example:

1) at t0, issue a new IO, rq is allocated, and blk_account_io_start()
update io_ticks;

2) something is wrong with drivers, and the rq can't be dispatched;

3) at t0 + 10s, drivers recovers and rq is dispatched and done, io_ticks
is updated;

Then if user is using "iostat 1" to monitor "util", between t0 - t0+9s,
util will be zero, and between t0+9s - t0+10s, util will be 1000%.

Fix this problem by updating io_ticks from diskstats_show() and
part_stat_show() if there are rq allocated.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20240509123717.3223892-3-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/genhd.c b/block/genhd.c
index 8f1163d2d17166ed71bd33a1a565e118f2bc3855..7f39fbe6075357d08d157ae0887f5b68de1d9690 100644 (file)
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -951,15 +951,10 @@ ssize_t part_stat_show(struct device *dev,
                       struct device_attribute *attr, char *buf)
 {
        struct block_device *bdev = dev_to_bdev(dev);
-       struct request_queue *q = bdev_get_queue(bdev);
        struct disk_stats stat;
        unsigned int inflight;
 
-       if (queue_is_mq(q))
-               inflight = blk_mq_in_flight(q, bdev);
-       else
-               inflight = part_in_flight(bdev);
-
+       inflight = part_in_flight(bdev);
        if (inflight) {
                part_stat_lock();
                update_io_ticks(bdev, jiffies, true);
@@ -1256,11 +1251,8 @@ 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;
-               if (queue_is_mq(gp->queue))
-                       inflight = blk_mq_in_flight(gp->queue, hd);
-               else
-                       inflight = part_in_flight(hd);
 
+               inflight = part_in_flight(hd);
                if (inflight) {
                        part_stat_lock();
                        update_io_ticks(hd, jiffies, true);