This reverts commit 0006707723233cb2a9a23ca19fc3d0864835704c. It has a
couple problems:
* bio_issue_time() is stored in bio->bi_issue truncated to 51 bits. This
overflows in slightly over 26 days. Setting rq->io_start_time_ns with it
means that io duration calculation would yield >26days after 26 days of
uptime. This, for example, confuses kyber making it cause high IO
latencies.
* rq->io_start_time_ns should record the time that the IO is issued to the
device so that on-device latency can be measured. However,
bio_issue_time() is set before the bio goes through the rq-qos controllers
(wbt, iolatency, iocost), so when the bio gets throttled in any of the
mechanisms, the measured latencies make no sense - on-device latencies end
up higher than request-alloc-to-completion latencies.
We'll need a smarter way to avoid calling ktime_get_ns() repeatedly
back-to-back. For now, let's revert the commit.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v5.16+
---
block/blk-mq.c | 9 +--------
1 file changed, 1 insertion(+), 8 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index c4370d2761706..84d749511f551 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1131,14 +1131,7 @@ void blk_mq_start_request(struct request *rq)
trace_block_rq_issue(rq);
if (test_bit(QUEUE_FLAG_STATS, &q->queue_flags)) {
- u64 start_time;
-#ifdef CONFIG_BLK_CGROUP
- if (rq->bio)
- start_time = bio_issue_time(&rq->bio->bi_issue);
- else
-#endif
- start_time = ktime_get_ns();
- rq->io_start_time_ns = start_time;
+ rq->io_start_time_ns = ktime_get_ns();
rq->stats_sectors = blk_rq_sectors(rq);
rq->rq_flags |= RQF_STATS;
rq_qos_issue(q, rq);
--
2.36.0
