whose device driver uses the blk-mq interface. Currently "dev -d"
always displays 0 in all fields for the blk-mq disk because blk-mq
does not increment/decrement request_list.count[2] on I/O creation
and I/O completion. The following values are used in blk-mq in such
situations:
- I/O creation: blk_mq_ctx.rq_dispatched[2]
- I/O completion: blk_mq_ctx.rq_completed[2]
So, we can get the counter of in-progress I/Os as follows:
in progress I/Os == rq_dispatched - rq_completed
This patch displays the result of above calculation for the disk.
It determines whether the device driver uses blk-mq if the
request_queue.mq_ops is not NULL. The "DRV" field is displayed as
"N/A(MQ)" if the value for in-flight in the device driver does not
exist for blk-mq.
(m.mizuma@jp.fujitsu.com)
