From: Jens Axboe <axboe@kernel.dk>
To: Jianchao Wang <jianchao.w.wang@oracle.com>
Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH V2] blk-mq: insert rq with DONTPREP to hctx dispatch list when requeue
Date: Mon, 11 Feb 2019 19:51:27 -0700 [thread overview]
Message-ID: <077964ab-0502-49ab-132d-657d32df7461@kernel.dk> (raw)
In-Reply-To: <1549936585-1702-1-git-send-email-jianchao.w.wang@oracle.com>
On 2/11/19 6:56 PM, Jianchao Wang wrote:
> When requeue, if RQF_DONTPREP, rq has contained some driver
> specific data, so insert it to hctx dispatch list to avoid any
> merge. Take scsi as example, here is the trace event log (no
> io scheduler, because RQF_STARTED would prevent merging),
>
> kworker/0:1H-339 [000] ...1 2037.209289: block_rq_insert: 8,0 R 4096 () 32768 + 8 [kworker/0:1H]
> scsi_inert_test-1987 [000] .... 2037.220465: block_bio_queue: 8,0 R 32776 + 8 [scsi_inert_test]
> scsi_inert_test-1987 [000] ...2 2037.220466: block_bio_backmerge: 8,0 R 32776 + 8 [scsi_inert_test]
> kworker/0:1H-339 [000] .... 2047.220913: block_rq_issue: 8,0 R 8192 () 32768 + 16 [kworker/0:1H]
> scsi_inert_test-1996 [000] ..s1 2047.221007: block_rq_complete: 8,0 R () 32768 + 8 [0]
> scsi_inert_test-1996 [000] .Ns1 2047.221045: block_rq_requeue: 8,0 R () 32776 + 8 [0]
> kworker/0:1H-339 [000] ...1 2047.221054: block_rq_insert: 8,0 R 4096 () 32776 + 8 [kworker/0:1H]
> kworker/0:1H-339 [000] ...1 2047.221056: block_rq_issue: 8,0 R 4096 () 32776 + 8 [kworker/0:1H]
> scsi_inert_test-1986 [000] ..s1 2047.221119: block_rq_complete: 8,0 R () 32776 + 8 [0]
>
> (32768 + 8) was requeued by scsi_queue_insert and had RQF_DONTPREP.
> Then it was merged with (32776 + 8) and issued. Due to RQF_DONTPREP,
> the sdb only contained the part of (32768 + 8), then only that part
> was completed. The lucky thing was that scsi_io_completion detected
> it and requeued the remaining part. So we didn't get corrupted data.
> However, the requeue of (32776 + 8) is not expected.
Looks good to me, I'll add this for 5.0.
--
Jens Axboe
next prev parent reply other threads:[~2019-02-12 2:51 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-12 1:56 [PATCH V2] blk-mq: insert rq with DONTPREP to hctx dispatch list when requeue Jianchao Wang
2019-02-12 2:51 ` Jens Axboe [this message]
2019-02-15 2:00 ` Ming Lei
2019-02-15 2:34 ` jianchao.wang
2019-02-15 3:14 ` Ming Lei
2019-02-15 3:41 ` jianchao.wang
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