On 10/13/2017 01:08 PM, Jens Axboe wrote: > On 10/13/2017 12:05 PM, Ming Lei wrote: >> Hi Jens, >> >> In Red Hat internal storage test wrt. blk-mq scheduler, we found that I/O >> performance is much bad with mq-deadline, especially about sequential I/O >> on some multi-queue SCSI devcies(lpfc, qla2xxx, SRP...) >> >> Turns out one big issue causes the performance regression: requests are >> still dequeued from sw queue/scheduler queue even when ldd's queue is >> busy, so I/O merge becomes quite difficult to make, then sequential IO >> performance degrades a lot. >> >> This issue becomes one of mains reasons for reverting default SCSI_MQ >> in V4.13. >> >> This 8 patches improve this situation, and brings back performance loss. >> >> With this change, SCSI-MQ sequential I/O performance is improved much, Paolo >> reported that mq-deadline performance improved much[2] in his dbench test >> wrt V2. Also performance improvement on lpfc/qla2xx was observed with V1.[1] >> >> [1] http://marc.info/?l=linux-block&m=150151989915776&w=2 >> [2] https://marc.info/?l=linux-block&m=150217980602843&w=2 > > I wanted to run some sanity testing on this series before committing it, > and unfortunately it doesn't even boot for me. Just hangs after loading > the kernel. Maybe an error slipped in for v8/9? Or it might be something with kyber, my laptop defaults to that. Test box seems to boot (which is SCSI), and nvme loads fine by default, but not with kyber. I don't have time to look into this more today, but the above might help you figure out what is going on. -- Jens Axboe
