Re: [PATCH V5 0/6] blk-mq: improvement CPU hotplug

[John Garry <john.garry@huawei.com>]

+- Keith

On 31/01/2020 10:58, Ming Lei wrote:
> On Fri, Jan 31, 2020 at 6:24 PM John Garry <john.garry@huawei.com> wrote:
>>
>>>> [  141.976109] Call trace:
>>>> [  141.978550]  __switch_to+0xbc/0x218
>>>> [  141.982029]  blk_mq_run_work_fn+0x1c/0x28
>>>> [  141.986027]  process_one_work+0x1e0/0x358
>>>> [  141.990025]  worker_thread+0x40/0x488
>>>> [  141.993678]  kthread+0x118/0x120
>>>> [  141.996897]  ret_from_fork+0x10/0x18
>>>
>>> Hi John,
>>>
>>> Thanks for your test!
>>>
>>
>> Hi Ming,
>>
>>> Could you test the following patchset and only the last one is changed?
>>>
>>> https://github.com/ming1/linux/commits/my_for_5.6_block
>>
>> For SCSI testing, I will ask my colleague Xiang Chen to test when he
>> returns to work. So I did not see this issue for my SCSI testing for
>> your original v5, but I was only using 1x as opposed to maybe 20x SAS disks.
>>
>> BTW, did you test NVMe? For some reason I could not trigger a scenario
>> where we're draining the outstanding requests for a queue which is being
>> deactivated - I mean, the queues were always already quiesced.
> 
> I run cpu hotplug test on both NVMe and SCSI in KVM, and fio just runs
> as expected.
> 
> NVMe is often 1:1 mapping, so it might be a bit difficult to trigger
> draining in-flight IOs.

I generally have a 4:1 mapping for my NVMe cards - so many CPUs.

But more alarming is that I see this on every run:

[  246.378744] psci: CPU6 killed (polled 0 ms)
[  246.427955] irq_migrate_all_off_this_cpu: 3 callbacks suppressed
[  246.427956] IRQ 822: no longer affine to CPU7
[  246.438586] CPU7: shutdown
[  246.441300] psci: CPU7 killed (polled 0 ms)
[  247.015206] pcieport 0000:00:08.0: can't change power state from 
D3cold to D0 (config space inaccessible)
Jobs: 6[  267.503159] rcu: INFO: rcu_preempt detected stalls on 
CPUs/tasks:
[  267.509244] rcu: 25-...0: (1 GPs behind) 
idle=11e/1/0x4000000000000000 softirq=1175/1177 fqs=2626
[  267.518283] (detected by 0, t=5255 jiffies, g=14001, q=1787)
[  267.524016] Task dump for CPU 25:
[  267.527318] irqbalance      R  running task        0  1275      1 
0x00000002
[  267.534354] Call trace:
[  267.536790]  __switch_to+0xbc/0x218
[  267.540266]  0xffff800014c53d68
Jobs: 6 (f=6): [R(6)][96.0%][r=0KiB/s[  278.195193] nvme nvme1: 
controller is down; will reset: CSTS=0xffffffff, PCI_STATUS=0xffff
,w=0KiB/s][r=0,w=0 IOPS][eta 00m:[  278.205197] nvme nvme0: controller 
is down; will reset: CSTS=0xffffffff, PCI_STATUS=0xffff
Jobs: 6 (f=6): [R(6)][0.0%][r=0KiB/s,w=0KiB/s][r=0,w=0 IO[  330.523157] 
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
[  330.529242] rcu: 25-...0: (1 GPs behind) 
idle=11e/1/0x4000000000000000 softirq=1175/1177 fqs=10503
[  330.538366] (detected by 0, t=21010 jiffies, g=14001, q=2318)
[  330.544186] Task dump for CPU 25:
[  330.547488] irqbalance      R  running task        0  1275      1 
0x00000002
[  330.554523] Call trace:
[  330.556958]  __switch_to+0xbc/0x218
[  330.560434]  0xffff800014c53d68
[  393.543155] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
[  393.549242] rcu: 25-...0: (1 GPs behind) 
idle=11e/1/0x4000000000000000 softirq=1175/1177 fqs=18379
[  393.558366] (detected by 8, t=36765 jiffies, g=14001, q=2385)
[  393.564187] Task dump for CPU 25:
[  393.567488] irqbalance      R  running task        0  1275      1 
0x00000002
[  393.574523] Call trace:
[  393.576960]  __switch_to+0xbc/0x218
[  393.580435]  0xffff800014c53d68
[  456.567156] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
[  456.573246] rcu: 25-...0: (1 GPs behind) 
idle=11e/1/0x4000000000000000 softirq=1175/1177 fqs=26255
[  456.582389] (detected by 90, t=52520 jiffies, g=14001, q=2397)
[  456.588296] Task dump for CPU 25:
[  456.591601] irqbalance      R  running task        0  1275      1 
0x00000002
[  456.598638] Call trace:
[  456.601078]  __switch_to+0xbc/0x218
[  456.604556]  0xffff800014c53d68
[  519.587152] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
[  519.593235] rcu: 25-...0: (1 GPs behind) 
idle=11e/1/0x4000000000000000 softirq=1175/1177 fqs=34131
[  519.602357] (detected by 90, t=68275 jiffies, g=14001, q=2405)
[  519.608264] Task dump for CPU 25:
[  519.611566] irqbalance      R  running task        0  1275      1 
0x00000002
[  519.618601] Call trace:
[  519.621036]  __switch_to+0xbc/0x218
[  519.624511]  0xffff800014c53d68
[  582.603153] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
[  582.609236] rcu: 25-...0: (1 GPs behind) 
idle=11e/1/0x4000000000000000 softirq=1175/1177 fqs=42006
[  582.618358] (detected by 90, t=84029 jiffies, g=14001, q=2409)
[  582.624265] Task dump for CPU 25:
[  582.627567] irqbalance      R  running task        0  1275      1 
0x00000002
[  582.634601] Call trace:
[  582.637036]  __switch_to+0xbc/0x218
[  582.640511]  0xffff800014c53d68


I tested v5.5 and I cannot see this, but your branch is based in 5.5-rc2 
with lots of other stuff on top. The only thing I changed was 
nvme.use_threaded_interrupts = 1.

Note that I do see this with v5.5 for my hotplug test, as expected:
[  280.221917] nvme nvme1: I/O 114 QID 19 timeout, completion polledta 
01m:50s]

...so I'm not going insane.

Thanks,
John