On Sat, Jun 13, 2020 at 12:17:37AM +0530, Kashyap Desai wrote: > > On 11/06/2020 04:07, Ming Lei wrote: > > >> Using 12x SAS SSDs on hisi_sas v3 hw. mq-deadline results are > > >> included, but it is not always an appropriate scheduler to use. > > >> > > >> Tag depth 4000 (default) 260** > > >> > > >> Baseline: > > >> none sched: 2290K IOPS 894K > > >> mq-deadline sched: 2341K IOPS 2313K > > >> > > >> Final, host_tagset=0 in LLDD* > > >> none sched: 2289K IOPS 703K > > >> mq-deadline sched: 2337K IOPS 2291K > > >> > > >> Final: > > >> none sched: 2281K IOPS 1101K > > >> mq-deadline sched: 2322K IOPS 1278K > > >> > > >> * this is relevant as this is the performance in supporting but not > > >> enabling the feature > > >> ** depth=260 is relevant as some point where we are regularly waiting > > >> for > > >> tags to be available. Figures were are a bit unstable here for > > >> testing. > > John - > > I tried V7 series and debug further on mq-deadline interface. This time I > have used another setup since HDD based setup is not readily available for > me. > In fact, I was able to simulate issue very easily using single scsi_device > as well. BTW, this is not an issue with this RFC, but generic issue. > Since I have converted nr_hw_queue > 1 for Broadcom product using this RFC, > It becomes noticeable now. > > Problem - Using below command I see heavy CPU utilization on " > native_queued_spin_lock_slowpath". This is because kblockd work queue is > submitting IO from all the CPUs even though fio is bound to single CPU. > Lock contention from " dd_dispatch_request" is causing this issue. > > numactl -C 13 fio > single.fio --iodepth=32 --bs=4k --rw=randread --ioscheduler=none --numjobs=1 > --cpus_allowed_policy=split --ioscheduler=mq-deadline > --group_reporting --filename=/dev/sdd > > While running above command, ideally we expect only kworker/13 to be active. > But you can see below - All the CPU is attempting submission and lots of CPU > consumption is due to lock contention. > > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND > 2726 root 0 -20 0 0 0 R 56.5 0.0 0:53.20 > kworker/13:1H-k > 7815 root 20 0 712404 15536 2228 R 43.2 0.0 0:05.03 fio > 2792 root 0 -20 0 0 0 I 26.6 0.0 0:22.19 > kworker/18:1H-k > 2791 root 0 -20 0 0 0 I 19.9 0.0 0:17.17 > kworker/19:1H-k > 1419 root 0 -20 0 0 0 I 19.6 0.0 0:17.03 > kworker/20:1H-k > 2793 root 0 -20 0 0 0 I 18.3 0.0 0:15.64 > kworker/21:1H-k > 1424 root 0 -20 0 0 0 I 17.3 0.0 0:14.99 > kworker/22:1H-k > 2626 root 0 -20 0 0 0 I 16.9 0.0 0:14.68 > kworker/26:1H-k > 2794 root 0 -20 0 0 0 I 16.9 0.0 0:14.87 > kworker/23:1H-k > 2795 root 0 -20 0 0 0 I 16.9 0.0 0:14.81 > kworker/24:1H-k > 2797 root 0 -20 0 0 0 I 16.9 0.0 0:14.62 > kworker/27:1H-k > 1415 root 0 -20 0 0 0 I 16.6 0.0 0:14.44 > kworker/30:1H-k > 2669 root 0 -20 0 0 0 I 16.6 0.0 0:14.38 > kworker/31:1H-k > 2796 root 0 -20 0 0 0 I 16.6 0.0 0:14.74 > kworker/25:1H-k > 2799 root 0 -20 0 0 0 I 16.6 0.0 0:14.56 > kworker/28:1H-k > 1425 root 0 -20 0 0 0 I 16.3 0.0 0:14.21 > kworker/34:1H-k > 2746 root 0 -20 0 0 0 I 16.3 0.0 0:14.33 > kworker/32:1H-k > 2798 root 0 -20 0 0 0 I 16.3 0.0 0:14.50 > kworker/29:1H-k > 2800 root 0 -20 0 0 0 I 16.3 0.0 0:14.27 > kworker/33:1H-k > 1423 root 0 -20 0 0 0 I 15.9 0.0 0:14.10 > kworker/54:1H-k > 1784 root 0 -20 0 0 0 I 15.9 0.0 0:14.03 > kworker/55:1H-k > 2801 root 0 -20 0 0 0 I 15.9 0.0 0:14.15 > kworker/35:1H-k > 2815 root 0 -20 0 0 0 I 15.9 0.0 0:13.97 > kworker/56:1H-k > 1484 root 0 -20 0 0 0 I 15.6 0.0 0:13.90 > kworker/57:1H-k > 1485 root 0 -20 0 0 0 I 15.6 0.0 0:13.82 > kworker/59:1H-k > 1519 root 0 -20 0 0 0 I 15.6 0.0 0:13.64 > kworker/62:1H-k > 2315 root 0 -20 0 0 0 I 15.6 0.0 0:13.87 > kworker/58:1H-k > 2627 root 0 -20 0 0 0 I 15.6 0.0 0:13.69 > kworker/61:1H-k > 2816 root 0 -20 0 0 0 I 15.6 0.0 0:13.75 > kworker/60:1H-k > > > I root cause this issue - > > Block layer always queue IO on hctx context mapped to CPU-13, but hw queue > run from all the hctx context. > I noticed in my test hctx48 has queued all the IOs. No other hctx has queued > IO. But all the hctx is counting for "run". > > # cat hctx48/queued > 2087058 > > #cat hctx*/run > 151318 > 30038 > 83110 > 50680 > 69907 > 60391 > 111239 > 18036 > 33935 > 91648 > 34582 > 22853 > 61286 > 19489 > > Below patch has fix - "Run the hctx queue for which request was completed > instead of running all the hardware queue." > If this looks valid fix, please include in V8 OR I can post separate patch > for this. Just want to have some level of review from this discussion. > > diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c > index 0652acd..f52118f 100644 > --- a/drivers/scsi/scsi_lib.c > +++ b/drivers/scsi/scsi_lib.c > @@ -554,6 +554,7 @@ static bool scsi_end_request(struct request *req, > blk_status_t error, > struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(req); > struct scsi_device *sdev = cmd->device; > struct request_queue *q = sdev->request_queue; > + struct blk_mq_hw_ctx *mq_hctx = req->mq_hctx; > > if (blk_update_request(req, error, bytes)) > return true; > @@ -595,7 +596,8 @@ static bool scsi_end_request(struct request *req, > blk_status_t error, > !list_empty(&sdev->host->starved_list)) > kblockd_schedule_work(&sdev->requeue_work); > else > - blk_mq_run_hw_queues(q, true); > + blk_mq_run_hw_queue(mq_hctx, true); > + //blk_mq_run_hw_queues(q, true); This way may cause IO hang because ->device_busy is shared by all hctxs. Thanks, Ming
