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
