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Revert "block: inherit request start time from bio for BLK_CGROUP"
commit4cddeacad6
upstream. This reverts commit0006707723
. 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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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1 changed files with 1 additions and 8 deletions
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@ -1122,14 +1122,7 @@ void blk_mq_start_request(struct request *rq)
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trace_block_rq_issue(rq);
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if (test_bit(QUEUE_FLAG_STATS, &q->queue_flags)) {
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u64 start_time;
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#ifdef CONFIG_BLK_CGROUP
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if (rq->bio)
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start_time = bio_issue_time(&rq->bio->bi_issue);
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else
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#endif
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start_time = ktime_get_ns();
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rq->io_start_time_ns = start_time;
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rq->io_start_time_ns = ktime_get_ns();
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rq->stats_sectors = blk_rq_sectors(rq);
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rq->rq_flags |= RQF_STATS;
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rq_qos_issue(q, rq);
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