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
Please comment & review, thanks!
https://github.com/ming1/linux/commits/v5.6-blk-mq-improve-cpu-hotplug
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 (8):
blk-mq: assign rq->tag in blk_mq_get_driver_tag
blk-mq: add new state of BLK_MQ_S_INACTIVE
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: re-submit IO in case that hctx is inactive
blk-mq: handle requests dispatched from IO scheduler in case of
inactive hctx
block: deactivate hctx when the hctx is actually inactive
block/blk-flush.c | 143 +++++++++++++---
block/blk-mq-debugfs.c | 2 +
block/blk-mq-tag.c | 2 +-
block/blk-mq-tag.h | 2 +
block/blk-mq.c | 331 ++++++++++++++++++++++++++++++-------
block/blk-mq.h | 24 +--
block/blk.h | 9 +-
drivers/block/loop.c | 2 +-
drivers/md/dm-rq.c | 2 +-
include/linux/blk-mq.h | 6 +
include/linux/cpuhotplug.h | 1 +
11 files changed, 420 insertions(+), 104 deletions(-)
Cc: John Garry <john.garry@xxxxxxxxxx>
Cc: Bart Van Assche <bvanassche@xxxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
--
2.25.2
