Re: [PATCH V4 0/5] blk-mq: improvement on handling IO during CPU hotplug

["chenxiang (M)" <chenxiang66@hisilicon.com>]

Hi,

在 2019/10/14 9:50, Ming Lei 写道:
> 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.

I tested those patchset with John's testcase, except dump_stack() in 
function __blk_mq_run_hw_queue() sometimes occurs  which don't
affect the function, it solves the CPU hotplug issue, so add tested-by 
for those patchset:

Tested-by: Xiang Chen <chenxiang66@hisilicon.com>

>
> V4:
> 	- resubmit IOs in dispatch list in case that this hctx is dead
>
> 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
> 	- address comments from John Garry and Minwoo
>
>
>
> Ming Lei (5):
>    blk-mq: add new state of BLK_MQ_S_INTERNAL_STOPPED
>    blk-mq: prepare for draining IO when hctx's all CPUs are offline
>    blk-mq: stop to handle IO and drain IO before hctx becomes dead
>    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
>
>   block/blk-mq-debugfs.c     |   2 +
>   block/blk-mq-tag.c         |   2 +-
>   block/blk-mq-tag.h         |   2 +
>   block/blk-mq.c             | 137 ++++++++++++++++++++++++++++++++++---
>   block/blk-mq.h             |   3 +-
>   drivers/block/loop.c       |   2 +-
>   drivers/md/dm-rq.c         |   2 +-
>   include/linux/blk-mq.h     |   5 ++
>   include/linux/cpuhotplug.h |   1 +
>   9 files changed, 141 insertions(+), 15 deletions(-)
>
> Cc: John Garry <john.garry@huawei.com>
> Cc: Bart Van Assche <bvanassche@acm.org>
> Cc: Hannes Reinecke <hare@suse.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Keith Busch <keith.busch@intel.com>
>