Re: [PATCH V2 0/5] blk-mq: improvement on handling IO during CPU hotplug

[Jens Axboe <axboe@kernel.dk>]

On 10/2/19 3:56 AM, John Garry wrote:
> On 22/08/2019 18:39, John Garry wrote:
>> On 12/08/2019 14:43, Ming Lei wrote:
>>> Hi,
>>>
>>> Thomas mentioned:
>>>      "
>>>       That was the constraint of managed interrupts from the very
>>> beginning:
>>>
>>>        The driver/subsystem has to quiesce the interrupt line and the
>>> associated
>>>        queue _before_ it gets shutdown in CPU unplug and not fiddle
>>> with it
>>>        until it's restarted by the core when the CPU is plugged in again.
>>>      "
>>>
>>> But no drivers or blk-mq do that before one hctx becomes dead(all
>>> CPUs for one hctx are offline), and even it is worse, blk-mq stills tries
>>> to run hw queue after hctx is dead, see blk_mq_hctx_notify_dead().
>>>
>>> This patchset tries to address the issue by two stages:
>>>
>>> 1) add one new cpuhp state of CPUHP_AP_BLK_MQ_ONLINE
>>>
>>> - mark the hctx as internal stopped, and drain all in-flight requests
>>> if the hctx is going to be dead.
>>>
>>> 2) re-submit IO in the state of CPUHP_BLK_MQ_DEAD after the hctx
>>> becomes dead
>>>
>>> - steal bios from the request, and resubmit them via
>>> generic_make_request(),
>>> then these IO will be mapped to other live hctx for dispatch
>>>
>>> Please comment & review, thanks!
>>>
>>> V2:
>>>      - patch4 & patch 5 in V1 have been merged to block tree, so remove
>>>        them
>>>      - address comments from John Garry and Minwoo
>>>
>>>
>>> Ming Lei (5):
>>>    blk-mq: add new state of BLK_MQ_S_INTERNAL_STOPPED
>>>    blk-mq: add blk-mq flag of BLK_MQ_F_NO_MANAGED_IRQ
>>>    blk-mq: stop to handle IO before hctx's all CPUs become offline
>>>    blk-mq: re-submit IO in case that hctx is dead
>>>    blk-mq: handle requests dispatched from IO scheduler in case that hctx
>>>      is dead
>>
>> Hi Ming,
>>
>> This looks to fix the hotplug issue for me.
>>
>> Previously I could manufacture a scenario while running fio where I got
>> IO timeouts, like this:
>>
>> root@(none)$ echo 0 > ./sys/devices/system/cpu/cpu0/online
>> [  296.897627] process 891 (fio) no longer affine to cpu0
>> [  296.898488] process 893 (fio) no longer affine to cpu0
>> [  296.910270] process 890 (fio) no longer affine to cpu0
>> [  296.927322] IRQ 775: no longer affine to CPU0
>> [  296.932762] CPU0: shutdown
>> [  296.935469] psci: CPU0 killed.
>> root@(none)$ [  326.971962] sas: Enter sas_scsi_recover_host busy: 61
>> failed: 61
>> [  326.977978] sas: sas_scsi_find_task: aborting task 0x00000000e2cdc79b
>> root@(none)$ [  333.047964] hisi_sas_v3_hw 0000:74:02.0: internal task
>> abort: timeout and not done.
>> [  333.055616] hisi_sas_v3_hw 0000:74:02.0: abort task: internal abort (-5)
>> [  333.062306] sas: sas_scsi_find_task: querying task 0x00000000e2cdc79b
>> [  333.068776] sas: sas_scsi_find_task: task 0x00000000e2cdc79b not at LU
>> [  333.075295] sas: task 0x00000000e2cdc79b is not at LU: I_T recover
>> [  333.081464] sas: I_T nexus reset for dev 5000c500a7b95a49
>>
>> Please notice the 30-second delay for the SCSI IO timeout.
>>
>> And now I don't see it; here's a sample for irq shutdown:
>> root@(none)$ echo 0 > ./sys/devices/system/cpu/cpu0/online
>> [  344.608148] process 849 (fio) no longer affine to cpu0
>> [  344.608639] process 848 (fio) no longer affine to cpu0
>> [  344.609454] process 850 (fio) no longer affine to cpu0
>> [  344.643481] process 847 (fio) no longer affine to cpu0
>> [  346.213842] IRQ 775: no longer affine to CPU0
>> [  346.219712] CPU0: shutdown
>> [  346.222425] psci: CPU0 killed.
>>
>> Please notice the ~1.5s pause, which would be the queue draining.
>>
>> So FWIW:
>> Tested-by: John Garry <john.garry@huawei.com>
>>
>> JFYI, I tested on 5.3-rc5 and cherry-picked
>> https://github.com/ming1/linux/commit/0d2cd3c99bb0fe81d2c0ca5d68e02bdc4521d4d6
>> and "blk-mq: add callback of .cleanup_rq".
>>
>> Cheers,
>> John
> 
> Hi Jens,
> 
> I don't mean to be pushy, but can we consider to get these patches from
> Ming merged?
> 
> As above, I tested on my SCSI driver and it works. I also tested on an
> NVMe disk, and it solves the condition which generates this message:
> root@(none)$ echo 0 > /sys/devices/system/cpu/cpu2/online
> [  465.635960] CPU2: shutdown
> [  465.638662] psci: CPU2 killed.
> [  111.381653] nvme nvme0: I/O 705 QID 18 timeout, completion polled
> 
> (that's on top off v5.4-rc1)

Ming, can you repost the series?

-- 
Jens Axboe