lkml.org 
[lkml]   [2017]   [Oct]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH V5 00/14] blk-mq-sched: improve sequential I/O performance(part 1)
From
Date
On 30/09/2017 11:27, 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
>

I tested this series for the SAS controller on HiSilicon hip07 platform
as I am interested in enabling MQ for this driver. Driver is
./drivers/scsi/hisi_sas/.

So I found that that performance is improved when enabling default
SCSI_MQ with this series vs baseline. However, it is still not as a good
as when default SCSI_MQ is disabled.

Here are some figures I got with fio:
4.14-rc2 without default SCSI_MQ
read, rw, write IOPS
952K, 133K/133K, 800K

4.14-rc2 with default SCSI_MQ
read, rw, write IOPS
311K, 117K/117K, 320K

This series* without default SCSI_MQ
read, rw, write IOPS
975K, 132K/132K, 790K

This series* with default SCSI_MQ
read, rw, write IOPS
770K, 164K/164K, 594K

Please note that hisi_sas driver does not enable mq by exposing multiple
queues to upper layer (even though it has multiple queues). I have been
playing with enabling it, but my performance is always worse...

* I'm using
https://github.com/ming1/linux/commits/blk_mq_improve_scsi_mpath_perf_V5.1,
as advised by Ming Lei.

Thanks,
John

> 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(-)
>


\
 
 \ /
  Last update: 2017-10-09 14:12    [W:0.201 / U:0.680 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site