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. Please comment & review, thanks! https://github.com/ming1/linux/commits/v5.7-rc-blk-mq-improve-cpu-hotplug 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 (9): blk-mq: mark blk_mq_get_driver_tag as static blk-mq: assign rq->tag in blk_mq_get_driver_tag blk-mq: prepare for draining IO when hctx's all CPUs are offline blk-mq: support rq filter callback when iterating rqs 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 | 39 ++-- block/blk-mq-tag.h | 4 + block/blk-mq.c | 384 ++++++++++++++++++++++++++++++------- block/blk-mq.h | 25 ++- 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, 495 insertions(+), 122 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