diff options
| author | Tejun Heo <tj@kernel.org> | 2022-04-27 09:49:12 -1000 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2022-04-27 13:51:28 -0600 |
| commit | 4cddeacad6d4b23493a108d0705e7d2ab89ba5a3 (patch) | |
| tree | 4cd48b87f9ee474a66de078d79d2bc1bc5625443 /block | |
| parent | 8c936f9ea11ec4e35e288810a7503b5c841a355f (diff) | |
Revert "block: inherit request start time from bio for BLK_CGROUP"
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@kernel.org>
Cc: stable@vger.kernel.org # v5.16+
Link: https://lore.kernel.org/r/YmmeOLfo5lzc+8yI@slm.duckdns.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
| -rw-r--r-- | block/blk-mq.c | 9 |
1 files changed, 1 insertions, 8 deletions
diff --git a/block/blk-mq.c b/block/blk-mq.c index c4370d276170..84d749511f55 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); |