From 4cddeacad6d4b23493a108d0705e7d2ab89ba5a3 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Wed, 27 Apr 2022 09:49:12 -1000 Subject: 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 Cc: stable@vger.kernel.org # v5.16+ Link: https://lore.kernel.org/r/YmmeOLfo5lzc+8yI@slm.duckdns.org Signed-off-by: Jens Axboe --- block/blk-mq.c | 9 +-------- 1 file changed, 1 insertion(+), 8 deletions(-) (limited to 'block/blk-mq.c') 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); -- cgit v1.2.3