> -----Original Message-----
> From: Ming Lei [mailto:ming....@redhat.com]
> Sent: Friday, February 9, 2018 11:01 AM
> To: Kashyap Desai
> Cc: Hannes Reinecke; Jens Axboe; linux-bl...@vger.kernel.org; Christoph
> Hellwig; Mike Snitzer; linux-scsi@vger.kernel.org; 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 Fri, Feb 09, 2018 at 10:28:23AM +0530, Kashyap Desai wrote:
> > > -----Original Message-----
> > > From: Ming Lei [mailto:ming....@redhat.com]
> > > Sent: Thursday, February 8, 2018 10:23 PM
> > > To: Hannes Reinecke
> > > Cc: Kashyap Desai; Jens Axboe; linux-bl...@vger.kernel.org;
> > > Christoph Hellwig; Mike Snitzer; linux-scsi@vger.kernel.org; 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....@redhat.com]
> > > > >> Sent: Wednesday, February 7, 2018 5:53 PM
> > > > >> To: Hannes Reinecke
> > > > >> Cc: Kashyap Desai; Jens Axboe; linux-bl...@vger.kernel.org;
> > > > >> Christoph Hellwig; Mike Snitzer; linux-scsi@vger.kernel.org;
> > > > >> 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.

I  will be doing some more testing and post you my findings.

>
> 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?

NO.  For CPU Lock up we need irq poll interface to quit from ISR loop of
the driver.

>
>
> Thanks,
> Ming

Reply via email to