On Fri, Oct 13, 2017 at 02:23:07PM -0600, Jens Axboe wrote: > 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. This issue can be fixed by the following one line change: --- diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c index f58cab82105b..94df3ce99f2f 100644 --- a/block/kyber-iosched.c +++ b/block/kyber-iosched.c @@ -641,7 +641,7 @@ static bool kyber_has_work(struct blk_mq_hw_ctx *hctx) if (!list_empty_careful(&khd->rqs[i])) return true; } - return false; + return sbitmap_any_bit_set(&hctx->ctx_map); } #define KYBER_LAT_SHOW_STORE(op) \ -- Ming
