From mboxrd@z Thu Jan  1 00:00:00 1970
From: Arkadiusz Miskiewicz <a.miskiewicz@gmail.com>
Subject: runtime change of use_blk_mq ?
Date: Thu, 11 Aug 2016 00:49:44 +0200
Message-ID: <201608110049.44832.a.miskiewicz@gmail.com>
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Hi.

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.

-- 
Arkadiusz Miśkiewicz, arekm / ( maven.pl | pld-linux.org )