linux-kernel - [PATCH for-6.10/block 2/2] block: fix that util can be greater than 100%

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Date: Thu,  9 May 2024 20:37:17 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: axboe@...nel.dk,
	ming.lei@...hat.com,
	hch@...radead.org,
	mpatocka@...hat.com,
	snitzer@...hat.com
Cc: linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	yukuai3@...wei.com,
	yukuai1@...weicloud.com,
	yi.zhang@...wei.com,
	yangerkun@...wei.com
Subject: [PATCH for-6.10/block 2/2] block: fix that util can be greater than 100%

From: Yu Kuai <yukuai3@...wei.com>

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@...wei.com>
---
 block/genhd.c | 12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c
index 8f1163d2d171..7f39fbe60753 100644
--- 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);
-- 
2.39.2