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

[Matthew Wilcox <willy@linux.intel.com>]

On Fri, Apr 08, 2016 at 01:29:26PM +0200, 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:

If there's a general block-mq bitching session, I have some ideas :-)

 - Inability to use all queues supported by a device.  Intel's P3700
   supports 31 queues, but block-mq insists on assigning an even multiple
   of CPUs to each queue.  So if you have 48 CPUs, it will use 24 queues.
   If you have 128 CPUs, it will only use 16 of the queues.

 - Interrupt steering needs to be controlled by block-mq instead of
   the driver.  It's pointless to have each driver implement its own
   policies on interrupt steering, irqbalanced remains a source of
   end-user frustration, and block-mq can change the queue<->cpu mapping
   without the driver's knowledge.

(thanks to Keith for his input on the first and suggestion of the second).