On Tue, Jul 31, 2018 at 12:02:15PM +0800, Jianchao Wang wrote:

Currently, we will always set SCHED_RESTART whenever there are
requests in hctx->dispatch, then when request is completed and
freed the hctx queues will be restarted to avoid IO hang. This
is unnecessary most of time. Especially when there are lots of
LUNs attached to one host, the RR restart loop could be very
expensive.

The big RR restart loop has been killed in the following commit:

commit 97889f9ac24f8d2fc8e703ea7f80c162bab10d4d
Author: Ming Lei [off-list ref]
Date:   Mon Jun 25 19:31:48 2018 +0800

    blk-mq: remove synchronize_rcu() from blk_mq_del_queue_tag_set()


Thanks,
Ming