Re: [RFC PATCH 0/7] blk-mq: improvement on handling IO during CPU hotplug

From: John Garry <john.garry@huawei.com>
To: Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@kernel.dk>
Cc: <linux-block@vger.kernel.org>,
	"James E . J . Bottomley" <jejb@linux.ibm.com>,
	"Martin K . Petersen" <martin.petersen@oracle.com>,
	<linux-scsi@vger.kernel.org>,
	Bart Van Assche <bvanassche@acm.org>,
	"Hannes Reinecke" <hare@suse.com>, Christoph Hellwig <hch@lst.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Keith Busch <keith.busch@intel.com>
Subject: Re: [RFC PATCH 0/7] blk-mq: improvement on handling IO during CPU hotplug
Date: Tue, 16 Jul 2019 14:54:24 +0800	[thread overview]
Message-ID: <c2c83d98-2012-13af-ab46-5a28303c0f87@huawei.com> (raw)
In-Reply-To: <20190712024726.1227-1-ming.lei@redhat.com>

在 12/07/2019 10:47, 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!
> 

Hi Ming,

FWIW, to me this series looks reasonable.

So you have plans to post an updated "[PATCH 0/9] blk-mq/scsi: convert 
private reply queue into blk_mq hw queue" then?

All the best,
John

> 
> Ming Lei (7):
>    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: add callback of .free_request
>    SCSI: implement .free_request callback
>    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             | 147 ++++++++++++++++++++++++++++++++++---
>   block/blk-mq.h             |   3 +-
>   drivers/block/loop.c       |   2 +-
>   drivers/md/dm-rq.c         |   2 +-
>   drivers/scsi/scsi_lib.c    |  13 ++++
>   include/linux/blk-mq.h     |  12 +++
>   include/linux/cpuhotplug.h |   1 +
>   10 files changed, 170 insertions(+), 16 deletions(-)
> 
> 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>
> 
> 