On 10/13/2017 01:21 PM, Jens Axboe wrote: > 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. Verified that the laptop boots just fine if I remove the kyber udev rule. -- Jens Axboe
