Re: [Lsf] [LSF/MM TOPIC] block-mq issues with FC

[Bart Van Assche <bart.vanassche@sandisk.com>]

On 04/08/2016 04:29 AM, Hannes Reinecke wrote:
> I'd like to propose a topic on block-mq issues with FC.
> During my performance testing using block/scsi-mq with FC I've hit
> several issues I'd like to discuss:
>
> - timeout handling:
> Out of necessity the status of any timed out command is undefined.
> So to be absolutely safe HBAs will be using extended timeouts here
> (eg 70secs for lpfc). During that time we _could_ signal I/O timeout
> to the upper layers, but then the tag will be reused, despite the
> HBA still having a reference to it.
> I'd like to discuss how this could be solved best with blk-mq.
>
> - Adaption on other HBAs to multiqueue:
> The current block-mq design assumes symmetric send and receive
> queues (in effect queue pairs). Any hardware _not_ providing this
> (like qla2xxx) can not be easily converted to scsi-mq. I'd like to
> discuss how one could approach converting these drivers.

Hello Hannes,

Without commenting on the specifics of the above proposal, I'm 
interested in a further discussion of how to improve multiqueue support 
for FC drivers.

Bart.