On Tue, Oct 17, 2017 at 01:04:16PM +0800, Ming Lei wrote:

Hi Jens,

The 1st patch runs idle hctx after dealy in scsi_mq_get_budget(),
so that we can keep same behaviour with before, and it can be
thought as a fix.

The 2nd patch cleans up RESTART, and removes handling for TAG_SHARED
from current blk-mq's RESTART mechanism because SCSI_MQ can covers its
restart by itself, so that no need to handle TAG_SHARED in blk-mq
RESTART. And >20% IOPS boost is observed in my rand read test over
scsi_debug.

John, please test this two patches and see if it may improve your SAS
IO performance, and you can find the two patches in the following branch:

	https://github.com/ming1/linux/commits/blk_mq_improve_restart_V1

Forget to mention, you need to either pull the above branch directly
or apply the two patches against for-next branch of Jens' block
tree:

	git://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git #for-next

-- 
Ming