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

[Ming Lei <ming.lei@redhat.com>]

On Wed, Oct 02, 2019 at 08:36:52AM -0600, Jens Axboe wrote:
> 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?

It has been resent out just now.

Thanks,
Ming