Re: [RFC] blk-mq: clean up the hctx restart

[Bart Van Assche]

On Wed, 2018-08-01 at 16:58 +-0800, Ming Lei wrote:
+AD4- On Wed, Aug 01, 2018 at 10:17:30AM +-0800, jianchao.wang wrote:
+AD4- +AD4- However, due to the limits in hctx+AF8-may+AF8-queue, q+AF8-b still cannot get the
+AD4- +AD4- tags. The RR restart also will not wake up q+AF8-a.
+AD4- +AD4- This is unfair for q+AF8-a.
+AD4- +AD4- 
+AD4- +AD4- When we remove RR restart fashion, at least, the q+AF8-a will be waked up by
+AD4- +AD4- the hctx restart.
+AD4- +AD4- Is this the improvement of fairness you said in driver tag allocation ?
+AD4- 
+AD4- I mean the fairness is totally covered by the general tag allocation
+AD4- algorithm now, which is sort of FIFO style because of waitqueue, but RR
+AD4- restart wakes up queue in the order of request queue.

>From sbitmap.h:

+ACM-define SBQ+AF8-WAIT+AF8-QUEUES 8

What do you think is the effect of your patch if more than eight LUNs are
active and the SCSI queue is full?

Thanks,

Bart.