On Sat, Sep 30, 2017 at 06:27:13PM +0800, 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 degrades a lot. > > This issue becomes one of mains reasons for reverting default SCSI_MQ > in V4.13. > > The 1st patch takes direct issue in blk_mq_request_bypass_insert(), > then we can improve dm-mpath's performance in part 2, which will > be posted out soon. > > The 2nd six patches improve this situation, and brings back > some 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 performanc > improvement on lpfc/qla2xx was observed with V1.[1] > > Please consider it for V4.15. > > [1] http://marc.info/?l=linux-block&m=150151989915776&w=2 > [2] https://marc.info/?l=linux-block&m=150217980602843&w=2 > > 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 (7): > blk-mq: issue rq directly in blk_mq_request_bypass_insert() > blk-mq-sched: fix scheduler bad performance > sbitmap: introduce __sbitmap_for_each_set() > blk-mq: introduce blk_mq_dequeue_from_ctx() > blk-mq-sched: move actual dispatching into one helper > blk-mq-sched: improve dispatching from sw queue > blk-mq-sched: don't dequeue request until all in ->dispatch are > flushed > > block/blk-core.c | 3 +- > block/blk-mq-debugfs.c | 1 + > block/blk-mq-sched.c | 104 ++++++++++++++++++++++++++++++++++++------- > block/blk-mq.c | 114 +++++++++++++++++++++++++++++++++++++++--------- > block/blk-mq.h | 4 +- > drivers/md/dm-rq.c | 2 +- > include/linux/blk-mq.h | 3 ++ > include/linux/sbitmap.h | 64 +++++++++++++++++++-------- > 8 files changed, 238 insertions(+), 57 deletions(-) Oops, the title should have been: [PATCH V5 0/7] blk-mq-sched: improve sequential I/O performance(part 1) Sorry for that. -- Ming
