[PATCH V9 00/11] blk-mq: improvement CPU hotplug

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

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 inactive(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

Thanks John Garry for running lots of tests on arm64 with this patchset
and co-working on investigating all kinds of issues.

Thanks Christoph's review on V7.

Please comment & review, thanks!

https://github.com/ming1/linux/commits/v5.7-rc-blk-mq-improve-cpu-hotplug

V9:
	- add Reviewed-by tag
	- document more on memory barrier usage between getting driver tag
	and handling cpu offline(7/11)
	- small code cleanup as suggested by Chritoph(7/11)
	- rebase against for-5.8/block(1/11, 2/11)
V8:
	- add patches to share code with blk_rq_prep_clone
	- code re-organization as suggested by Christoph, most of them are
	in 04/11, 10/11
	- add reviewed-by tag

V7:
	- fix updating .nr_active in get_driver_tag
	- add hctx->cpumask check in cpuhp handler
	- only drain requests which tag is >= 0
	- pass more aggressive cpuhotplug&io test

V6:
	- simplify getting driver tag, so that we can drain in-flight
	  requests correctly without using synchronize_rcu()
	- handle re-submission of flush & passthrough request correctly

V5:
	- rename BLK_MQ_S_INTERNAL_STOPPED as BLK_MQ_S_INACTIVE
	- re-factor code for re-submit requests in cpu dead hotplug handler
	- address requeue corner case

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 (11):
  block: clone nr_integrity_segments and write_hint in blk_rq_prep_clone
  block: add helper for copying request
  blk-mq: mark blk_mq_get_driver_tag as static
  blk-mq: assign rq->tag in blk_mq_get_driver_tag
  blk-mq: support rq filter callback when iterating rqs
  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 inactive
  block: add blk_end_flush_machinery
  blk-mq: add blk_mq_hctx_handle_dead_cpu for handling cpu dead
  blk-mq: re-submit IO in case that hctx is inactive
  block: deactivate hctx when the hctx is actually inactive

 block/blk-core.c           |  27 ++-
 block/blk-flush.c          | 141 ++++++++++++---
 block/blk-mq-debugfs.c     |   2 +
 block/blk-mq-tag.c         |  39 ++--
 block/blk-mq-tag.h         |   4 +
 block/blk-mq.c             | 352 +++++++++++++++++++++++++++++--------
 block/blk-mq.h             |  22 ++-
 block/blk.h                |  11 +-
 drivers/block/loop.c       |   2 +-
 drivers/md/dm-rq.c         |   2 +-
 include/linux/blk-mq.h     |   6 +
 include/linux/cpuhotplug.h |   1 +
 12 files changed, 477 insertions(+), 132 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>
-- 
2.25.2