block: default to QD=1 writes for blk-mq rotational zoned devices

block: default to QD=1 writes for blk-mq rotational zoned devices

For blk-mq rotational zoned block devices (e.g. SMR HDDs), default to
having zone write plugging limit write operations to a maximum queue
depth of 1 for all zones. This significantly reduce write seek overhead
and improves SMR HDD write throughput.

For remotely connected disks with a very high network latency this
features might not be useful. However, remotely connected zoned devices
are rare at the moment, and we cannot know the round trip latency to
pick a good default for network attached devices. System administrators
can however disable this feature in that case.

For BIO based (non blk-mq) rotational zoned block devices, the device
driver (e.g. a DM target driver) can directly set an appropriate
default.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>