On Fri, Feb 09, 2018 at 10:28:23AM +0530, Kashyap Desai wrote: > > -----Original Message----- > > From: Ming Lei [mailto:ming.lei@xxxxxxxxxx] > > Sent: Thursday, February 8, 2018 10:23 PM > > To: Hannes Reinecke > > Cc: Kashyap Desai; Jens Axboe; linux-block@xxxxxxxxxxxxxxx; Christoph > > Hellwig; Mike Snitzer; linux-scsi@xxxxxxxxxxxxxxx; Arun Easi; Omar > Sandoval; > > Martin K . Petersen; James Bottomley; Christoph Hellwig; Don Brace; > Peter > > Rivera; Paolo Bonzini; Laurence Oberman > > Subject: Re: [PATCH 0/5] blk-mq/scsi-mq: support global tags & introduce > > force_blk_mq > > > > On Thu, Feb 08, 2018 at 08:00:29AM +0100, Hannes Reinecke wrote: > > > On 02/07/2018 03:14 PM, Kashyap Desai wrote: > > > >> -----Original Message----- > > > >> From: Ming Lei [mailto:ming.lei@xxxxxxxxxx] > > > >> Sent: Wednesday, February 7, 2018 5:53 PM > > > >> To: Hannes Reinecke > > > >> Cc: Kashyap Desai; Jens Axboe; linux-block@xxxxxxxxxxxxxxx; > > > >> Christoph Hellwig; Mike Snitzer; linux-scsi@xxxxxxxxxxxxxxx; Arun > > > >> Easi; Omar > > > > Sandoval; > > > >> Martin K . Petersen; James Bottomley; Christoph Hellwig; Don Brace; > > > > Peter > > > >> Rivera; Paolo Bonzini; Laurence Oberman > > > >> Subject: Re: [PATCH 0/5] blk-mq/scsi-mq: support global tags & > > > >> introduce force_blk_mq > > > >> > > > >> On Wed, Feb 07, 2018 at 07:50:21AM +0100, Hannes Reinecke wrote: > > > >>> Hi all, > > > >>> > > > >>> [ .. ] > > > >>>>> > > > >>>>> Could you share us your patch for enabling global_tags/MQ on > > > >>>> megaraid_sas > > > >>>>> so that I can reproduce your test? > > > >>>>> > > > >>>>>> See below perf top data. "bt_iter" is consuming 4 times more > CPU. > > > >>>>> > > > >>>>> Could you share us what the IOPS/CPU utilization effect is after > > > >>>> applying the > > > >>>>> patch V2? And your test script? > > > >>>> Regarding CPU utilization, I need to test one more time. > > > >>>> Currently system is in used. > > > >>>> > > > >>>> I run below fio test on total 24 SSDs expander attached. > > > >>>> > > > >>>> numactl -N 1 fio jbod.fio --rw=randread --iodepth=64 --bs=4k > > > >>>> --ioengine=libaio --rw=randread > > > >>>> > > > >>>> Performance dropped from 1.6 M IOPs to 770K IOPs. > > > >>>> > > > >>> This is basically what we've seen with earlier iterations. > > > >> > > > >> Hi Hannes, > > > >> > > > >> As I mentioned in another mail[1], Kashyap's patch has a big issue, > > > > which > > > >> causes only reply queue 0 used. > > > >> > > > >> [1] https://marc.info/?l=linux-scsi&m=151793204014631&w=2 > > > >> > > > >> So could you guys run your performance test again after fixing the > > > > patch? > > > > > > > > Ming - > > > > > > > > I tried after change you requested. Performance drop is still > unresolved. > > > > From 1.6 M IOPS to 770K IOPS. > > > > > > > > See below data. All 24 reply queue is in used correctly. > > > > > > > > IRQs / 1 second(s) > > > > IRQ# TOTAL NODE0 NODE1 NAME > > > > 360 16422 0 16422 IR-PCI-MSI 70254653-edge megasas > > > > 364 15980 0 15980 IR-PCI-MSI 70254657-edge megasas > > > > 362 15979 0 15979 IR-PCI-MSI 70254655-edge megasas > > > > 345 15696 0 15696 IR-PCI-MSI 70254638-edge megasas > > > > 341 15659 0 15659 IR-PCI-MSI 70254634-edge megasas > > > > 369 15656 0 15656 IR-PCI-MSI 70254662-edge megasas > > > > 359 15650 0 15650 IR-PCI-MSI 70254652-edge megasas > > > > 358 15596 0 15596 IR-PCI-MSI 70254651-edge megasas > > > > 350 15574 0 15574 IR-PCI-MSI 70254643-edge megasas > > > > 342 15532 0 15532 IR-PCI-MSI 70254635-edge megasas > > > > 344 15527 0 15527 IR-PCI-MSI 70254637-edge megasas > > > > 346 15485 0 15485 IR-PCI-MSI 70254639-edge megasas > > > > 361 15482 0 15482 IR-PCI-MSI 70254654-edge megasas > > > > 348 15467 0 15467 IR-PCI-MSI 70254641-edge megasas > > > > 368 15463 0 15463 IR-PCI-MSI 70254661-edge megasas > > > > 354 15420 0 15420 IR-PCI-MSI 70254647-edge megasas > > > > 351 15378 0 15378 IR-PCI-MSI 70254644-edge megasas > > > > 352 15377 0 15377 IR-PCI-MSI 70254645-edge megasas > > > > 356 15348 0 15348 IR-PCI-MSI 70254649-edge megasas > > > > 337 15344 0 15344 IR-PCI-MSI 70254630-edge megasas > > > > 343 15320 0 15320 IR-PCI-MSI 70254636-edge megasas > > > > 355 15266 0 15266 IR-PCI-MSI 70254648-edge megasas > > > > 335 15247 0 15247 IR-PCI-MSI 70254628-edge megasas > > > > 363 15233 0 15233 IR-PCI-MSI 70254656-edge megasas > > > > > > > > > > > > Average: CPU %usr %nice %sys %iowait > %steal > > > > %irq %soft %guest %gnice %idle > > > > Average: 18 3.80 0.00 14.78 10.08 > 0.00 > > > > 0.00 4.01 0.00 0.00 67.33 > > > > Average: 19 3.26 0.00 15.35 10.62 > 0.00 > > > > 0.00 4.03 0.00 0.00 66.74 > > > > Average: 20 3.42 0.00 14.57 10.67 > 0.00 > > > > 0.00 3.84 0.00 0.00 67.50 > > > > Average: 21 3.19 0.00 15.60 10.75 > 0.00 > > > > 0.00 4.16 0.00 0.00 66.30 > > > > Average: 22 3.58 0.00 15.15 10.66 > 0.00 > > > > 0.00 3.51 0.00 0.00 67.11 > > > > Average: 23 3.34 0.00 15.36 10.63 > 0.00 > > > > 0.00 4.17 0.00 0.00 66.50 > > > > Average: 24 3.50 0.00 14.58 10.93 > 0.00 > > > > 0.00 3.85 0.00 0.00 67.13 > > > > Average: 25 3.20 0.00 14.68 10.86 > 0.00 > > > > 0.00 4.31 0.00 0.00 66.95 > > > > Average: 26 3.27 0.00 14.80 10.70 > 0.00 > > > > 0.00 3.68 0.00 0.00 67.55 > > > > Average: 27 3.58 0.00 15.36 10.80 > 0.00 > > > > 0.00 3.79 0.00 0.00 66.48 > > > > Average: 28 3.46 0.00 15.17 10.46 > 0.00 > > > > 0.00 3.32 0.00 0.00 67.59 > > > > Average: 29 3.34 0.00 14.42 10.72 > 0.00 > > > > 0.00 3.34 0.00 0.00 68.18 > > > > Average: 30 3.34 0.00 15.08 10.70 > 0.00 > > > > 0.00 3.89 0.00 0.00 66.99 > > > > Average: 31 3.26 0.00 15.33 10.47 > 0.00 > > > > 0.00 3.33 0.00 0.00 67.61 > > > > Average: 32 3.21 0.00 14.80 10.61 > 0.00 > > > > 0.00 3.70 0.00 0.00 67.67 > > > > Average: 33 3.40 0.00 13.88 10.55 > 0.00 > > > > 0.00 4.02 0.00 0.00 68.15 > > > > Average: 34 3.74 0.00 17.41 10.61 > 0.00 > > > > 0.00 4.51 0.00 0.00 63.73 > > > > Average: 35 3.35 0.00 14.37 10.74 > 0.00 > > > > 0.00 3.84 0.00 0.00 67.71 > > > > Average: 36 0.54 0.00 1.77 0.00 > 0.00 > > > > 0.00 0.00 0.00 0.00 97.69 > > > > .. > > > > Average: 54 3.60 0.00 15.17 10.39 > 0.00 > > > > 0.00 4.22 0.00 0.00 66.62 > > > > Average: 55 3.33 0.00 14.85 10.55 > 0.00 > > > > 0.00 3.96 0.00 0.00 67.31 > > > > Average: 56 3.40 0.00 15.19 10.54 > 0.00 > > > > 0.00 3.74 0.00 0.00 67.13 > > > > Average: 57 3.41 0.00 13.98 10.78 > 0.00 > > > > 0.00 4.10 0.00 0.00 67.73 > > > > Average: 58 3.32 0.00 15.16 10.52 > 0.00 > > > > 0.00 4.01 0.00 0.00 66.99 > > > > Average: 59 3.17 0.00 15.80 10.35 > 0.00 > > > > 0.00 3.86 0.00 0.00 66.80 > > > > Average: 60 3.00 0.00 14.63 10.59 > 0.00 > > > > 0.00 3.97 0.00 0.00 67.80 > > > > Average: 61 3.34 0.00 14.70 10.66 > 0.00 > > > > 0.00 4.32 0.00 0.00 66.97 > > > > Average: 62 3.34 0.00 15.29 10.56 > 0.00 > > > > 0.00 3.89 0.00 0.00 66.92 > > > > Average: 63 3.29 0.00 14.51 10.72 > 0.00 > > > > 0.00 3.85 0.00 0.00 67.62 > > > > Average: 64 3.48 0.00 15.31 10.65 > 0.00 > > > > 0.00 3.97 0.00 0.00 66.60 > > > > Average: 65 3.34 0.00 14.36 10.80 > 0.00 > > > > 0.00 4.11 0.00 0.00 67.39 > > > > Average: 66 3.13 0.00 14.94 10.70 > 0.00 > > > > 0.00 4.10 0.00 0.00 67.13 > > > > Average: 67 3.06 0.00 15.56 10.69 > 0.00 > > > > 0.00 3.82 0.00 0.00 66.88 > > > > Average: 68 3.33 0.00 14.98 10.61 > 0.00 > > > > 0.00 3.81 0.00 0.00 67.27 > > > > Average: 69 3.20 0.00 15.43 10.70 > 0.00 > > > > 0.00 3.82 0.00 0.00 66.85 > > > > Average: 70 3.34 0.00 17.14 10.59 > 0.00 > > > > 0.00 3.00 0.00 0.00 65.92 > > > > Average: 71 3.41 0.00 14.94 10.56 > 0.00 > > > > 0.00 3.41 0.00 0.00 67.69 > > > > > > > > Perf top - > > > > > > > > 64.33% [kernel] [k] bt_iter > > > > 4.86% [kernel] [k] blk_mq_queue_tag_busy_iter > > > > 4.23% [kernel] [k] _find_next_bit > > > > 2.40% [kernel] [k] native_queued_spin_lock_slowpath > > > > 1.09% [kernel] [k] sbitmap_any_bit_set > > > > 0.71% [kernel] [k] sbitmap_queue_clear > > > > 0.63% [kernel] [k] find_next_bit > > > > 0.54% [kernel] [k] _raw_spin_lock_irqsave > > > > > > > Ah. So we're spending quite some time in trying to find a free tag. > > > I guess this is due to every queue starting at the same position > > > trying to find a free tag, which inevitably leads to a contention. > > > > IMO, the above trace means that blk_mq_in_flight() may be the > bottleneck, > > and looks not related with tag allocation. > > > > Kashyap, could you run your performance test again after disabling > iostat by > > the following command on all test devices and killing all utilities > which may > > read iostat(/proc/diskstats, ...)? > > > > echo 0 > /sys/block/sdN/queue/iostat > > Ming - After changing iostat = 0 , I see performance issue is resolved. > > Below is perf top output after iostats = 0 > > > 23.45% [kernel] [k] bt_iter > 2.27% [kernel] [k] blk_mq_queue_tag_busy_iter > 2.18% [kernel] [k] _find_next_bit > 2.06% [megaraid_sas] [k] complete_cmd_fusion > 1.87% [kernel] [k] clflush_cache_range > 1.70% [kernel] [k] dma_pte_clear_level > 1.56% [kernel] [k] __domain_mapping > 1.55% [kernel] [k] sbitmap_queue_clear > 1.30% [kernel] [k] gup_pgd_range Hi Kashyap, Thanks for your test and update. Looks blk_mq_queue_tag_busy_iter() is still sampled by perf even though iostats is disabled, and I guess there may be utilities which are reading iostats a bit frequently. Either there is issue introduced in part_round_stats() recently since I remember that this counter should have been read at most one time during one jiffies in IO path, or the implementation of blk_mq_in_flight() can become a bit heavy in your environment. Jens may have idea about this issue. And I guess the lockup issue may be avoided by this approach now? Thanks, Ming
