Hi. By any chance, could this be backported to 4.14? I'm confused with "SCSI: allow to pass null rq to scsi_prep_state_check()" since it uses refactored flags. === if (req && !(req->rq_flags & RQF_PREEMPT)) === Is it safe to revert to REQ_PREEMPT here, or rq_flags should also be replaced with cmd_flags? Thanks. On sobota 14. října 2017 11:22:24 CEST 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 > > gitweb: > https://github.com/ming1/linux/commits/ blk_mq_improve_scsi_mpath_perf_V10_p > art1 > > V10: > - fix hang with kyber used > - address comments from Bart > > V9: > - change title of patch1 > - rename blk_mq_get_budget() as blk_mq_get_dispatch_budget() > - make check on .get_budget/.put_budget cleaner > - all are suggested by Jens, thank for review > > V8: > - introduce helper of blk_mq_get_budget > - handle failure path of get_budget > > V7: > - introduce .get_budget/.put_budget, and IO merge gets improved > compared with V6, and in theory this approach is better than the way > taken in block legacy > > - drop patch of 'blk-mq-sched: don't dequeue request until all in > ->dispatch are flushed' > > V6: > - address comments from Christoph > - drop the 1st patch which changes blk_mq_request_bypass_insert(), > which should belong to dm-mpath's improvement > - move ' blk-mq-sched: move actual dispatching into one helper' > as 2nd patch, and use the introduced helper to simplify dispatch > logic > - merge two previous patches into one for improving dispatch from sw queue > - make comment/commit log line width as ~70, as suggested by > Christoph > > V5: > - address some comments from Omar > - add Tested-by & Reveiewed-by tag > - use direct issue for blk_mq_request_bypass_insert(), and > start to consider to improve sequential I/O for dm-mpath > - only include part 1(the original patch 1 ~ 6), as suggested > by Omar > > V4: > - add Reviewed-by tag > - some trival change: typo fix in commit log or comment, > variable name, no actual functional change > > V3: > - totally round robin for picking req from ctx, as suggested > by Bart > - remove one local variable in __sbitmap_for_each_set() > - drop patches of single dispatch list, which can improve > performance on mq-deadline, but cause a bit degrade on > none because all hctxs need to be checked after ->dispatch > is flushed. Will post it again once it is mature. > - rebase on v4.13-rc6 with block for-next > > V2: > - dequeue request from sw queues in round roubin's style > as suggested by Bart, and introduces one helper in sbitmap > for this purpose > - improve bio merge via hash table from sw queue > - add comments about using DISPATCH_BUSY state in lockless way, > simplifying handling on busy state, > - hold ctx->lock when clearing ctx busy bit as suggested > by Bart > > > Ming Lei (8): > blk-mq-sched: dispatch from scheduler only after progress is made on > ->dispatch > blk-mq-sched: move actual dispatching into one helper > sbitmap: introduce __sbitmap_for_each_set() > block: kyber: check if there is request in ctx in kyber_has_work() > blk-mq: introduce .get_budget and .put_budget in blk_mq_ops > blk-mq-sched: improve dispatching from sw queue > SCSI: allow to pass null rq to scsi_prep_state_check() > SCSI: implement .get_budget and .put_budget for blk-mq > > block/blk-mq-sched.c | 148 > +++++++++++++++++++++++++++++++++++++++++------- block/blk-mq-sched.h | > 2 +- > block/blk-mq.c | 82 +++++++++++++++++++++++++-- > block/blk-mq.h | 22 ++++++- > block/kyber-iosched.c | 2 +- > drivers/scsi/scsi_lib.c | 79 ++++++++++++++++++-------- > include/linux/blk-mq.h | 13 +++++ > include/linux/sbitmap.h | 64 +++++++++++++++------ > 8 files changed, 342 insertions(+), 70 deletions(-)
