Re: [PATCH V3 0/5] blk-mq: improvement on handling IO during CPU hotplug

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

On 08/10/2019 05:18, 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!
>
> John, I don't add your tested-by tag since V3 have some changes,
> and I appreciate if you may run your test on V3.
>

Will do, Thanks

> V3:
> 	- re-organize patch 2 & 3 a bit for addressing Hannes's comment
> 	- fix patch 4 for avoiding potential deadlock, as found by Hannes
>
> V2:
> 	- patch4 & patch 5 in V1 have been merged to block tree, so remove
> 	  them
> 	- addres