On Mon, Oct 09, 2017 at 11:04:39PM +0800, Ming Lei wrote: > Hi John, > > On Mon, Oct 09, 2017 at 01:09:22PM +0100, John Garry wrote: > > 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 > > Thanks for testing this patchset! > > Looks there is big improvement, but the gap compared with > block legacy is not small too. > > > > > 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. > > Could you test on the following branch and see if it makes a > difference? > > https://github.com/ming1/linux/commits/blk_mq_improve_scsi_mpath_perf_V6.1_test Hi John, Please test the following branch directly: https://github.com/ming1/linux/tree/blk_mq_improve_scsi_mpath_perf_V6.2_test And code is simplified and cleaned up much in V6.2, then only two extra patches(top 2) are needed against V6 which was posted yesterday. Please test SCSI_MQ with mq-deadline, which should be the default mq scheduler on your HiSilicon SAS. -- Ming
