On 12/08/2019 14:43, Ming Lei wrote:
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!
V2:
- patch4 & patch 5 in V1 have been merged to block tree, so remove
them
- address comments from John Garry and Minwoo
Ming Lei (5):
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: re-submit IO in case that hctx is dead
blk-mq: handle requests dispatched from IO scheduler in case that hctx
is dead
Hi Ming,
This looks to fix the hotplug issue for me.
Previously I could manufacture a scenario while running fio where I got
IO timeouts, like this:
root@(none)$ echo 0 > ./sys/devices/system/cpu/cpu0/online
[ 296.897627] process 891 (fio) no longer affine to cpu0
[ 296.898488] process 893 (fio) no longer affine to cpu0
[ 296.910270] process 890 (fio) no longer affine to cpu0
[ 296.927322] IRQ 775: no longer affine to CPU0
[ 296.932762] CPU0: shutdown
[ 296.935469] psci: CPU0 killed.
root@(none)$ [ 326.971962] sas: Enter sas_scsi_recover_host busy: 61
failed: 61
[ 326.977978] sas: sas_scsi_find_task: aborting task 0x00000000e2cdc79b
root@(none)$ [ 333.047964] hisi_sas_v3_hw 0000:74:02.0: internal task
abort: timeout and not done.
[ 333.055616] hisi_sas_v3_hw 0000:74:02.0: abort task: internal abort (-5)
[ 333.062306] sas: sas_scsi_find_task: querying task 0x00000000e2cdc79b
[ 333.068776] sas: sas_scsi_find_task: task 0x00000000e2cdc79b not at LU
[ 333.075295] sas: task 0x00000000e2cdc79b is not at LU: I_T recover
[ 333.081464] sas: I_T nexus reset for dev 5000c500a7b95a49
Please notice the 30-second delay for the SCSI IO timeout.
And now I don't see it; here's a sample for irq shutdown:
root@(none)$ echo 0 > ./sys/devices/system/cpu/cpu0/online
[ 344.608148] process 849 (fio) no longer affine to cpu0
[ 344.608639] process 848 (fio) no longer affine to cpu0
[ 344.609454] process 850 (fio) no longer affine to cpu0
[ 344.643481] process 847 (fio) no longer affine to cpu0
[ 346.213842] IRQ 775: no longer affine to CPU0
[ 346.219712] CPU0: shutdown
[ 346.222425] psci: CPU0 killed.
Please notice the ~1.5s pause, which would be the queue draining.
So FWIW:
Tested-by: John Garry <john.garry@xxxxxxxxxx>
JFYI, I tested on 5.3-rc5 and cherry-picked
https://github.com/ming1/linux/commit/0d2cd3c99bb0fe81d2c0ca5d68e02bdc4521d4d6
and "blk-mq: add callback of .cleanup_rq".
Cheers,
John
block/blk-mq-debugfs.c | 2 +
block/blk-mq-tag.c | 2 +-
block/blk-mq-tag.h | 2 +
block/blk-mq.c | 143 +++++++++++++++++++++++++++++++++----
block/blk-mq.h | 3 +-
drivers/block/loop.c | 2 +-
drivers/md/dm-rq.c | 2 +-
include/linux/blk-mq.h | 5 ++
include/linux/cpuhotplug.h | 1 +
9 files changed, 146 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>
