On 08/10/2016 03:49 PM, Arkadiusz Miskiewicz wrote:
Is runtime enabling/disabling of blk-mq supported?
Doesn't seem to work here:
4.1.30 (but the same thing on 4.6.3):
# zcat /proc/config.gz |grep _MQ_DEF
# CONFIG_SCSI_MQ_DEFAULT is not set
# CONFIG_DM_MQ_DEFAULT is not set
# cat /sys/module/scsi_mod/parameters/use_blk_mq
N
# grep "" /sys/block/sd*/queue/scheduler
/sys/block/sda/queue/scheduler:noop [deadline] cfq
/sys/block/sdb/queue/scheduler:noop [deadline] cfq
/sys/block/sdc/queue/scheduler:noop [deadline] cfq
/sys/block/sdd/queue/scheduler:noop [deadline] cfq
/sys/block/sde/queue/scheduler:noop [deadline] cfq
/sys/block/sdf/queue/scheduler:noop [deadline] cfq
/sys/block/sdg/queue/scheduler:noop [deadline] cfq
# echo Y > /sys/module/scsi_mod/parameters/use_blk_mq
# cat /sys/module/scsi_mod/parameters/use_blk_mq
Y
# grep "" /sys/block/sd*/queue/scheduler
/sys/block/sda/queue/scheduler:noop [deadline] cfq
/sys/block/sdb/queue/scheduler:noop [deadline] cfq
/sys/block/sdc/queue/scheduler:noop [deadline] cfq
/sys/block/sdd/queue/scheduler:noop [deadline] cfq
/sys/block/sde/queue/scheduler:noop [deadline] cfq
/sys/block/sdf/queue/scheduler:noop [deadline] cfq
/sys/block/sdg/queue/scheduler:noop [deadline] cfq
so use_blk_mq is Y but queue/scheduler for existing devices still contains I/O
schedulers and shows deadline as active. Looks like blk-mq is not active.
Hello Arkadiusz,
From drivers/scsi/hosts.c, scsi_host_alloc():
shost->use_blk_mq = scsi_use_blk_mq && !shost->hostt->disable_blk_mq;
In other words, if you want the change of
/sys/module/scsi_mod/parameters/use_blk_mq to become effective, you will
have to trigger SCSI host removal and re-add. For a boot drive this is
not possible. But when using a SCSI-over-network driver unloading and
reloading the appropriate SCSI LLD should be sufficient. Some SCSI LLD
drivers, e.g. ib_srp, allow to log out and relogin without unloading and
reloading the kernel driver.
Bart.
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