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

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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@xxxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Keith Busch <keith.busch@xxxxxxxxx>







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