Re: [dpdk-dev] [PATCH] igb_uio: cap max VFs at 7 to reserve one for PF

["Richardson, Bruce" <bruce.richardson@intel.com>]

> -----Original Message-----
> From: Chris Wright [mailto:chrisw@redhat.com]
> Sent: Friday, June 13, 2014 10:52 AM
> To: Richardson, Bruce; Stephen Hemminger
> Cc: Thomas Monjalon; dev@dpdk.org
> Subject: [PATCH] igb_uio: cap max VFs at 7 to reserve one for PF
> 
> To keep from confusing users, cap max VFs at 7, despite PCI SR-IOV config
> space showing a max of 8.  This reserves a queue pair for the PF.
> 
> This issue was cited here:
> 
>  http://dpdk.org/ml/archives/dev/2014-April/001832.html
> 
> Cc: Bruce Richardson <bruce.richardson@intel.com>
> Cc: Stephen Hemminger <stephen@networkplumber.org>
> Signed-off-by: Chris Wright <chrisw@redhat.com>
> ---
> 
> This is what Linux kernel driver does.  I have only
> compile tested it.  Stephen sending to you and Bruce
> in case you want to Ack and add to your current queue.
> 

Sorry, NAK - at least for this implementation.

Hardcoding this to 7 is a bad idea, as the actual max number of VFs supported will depend on the actual hardware used. For someone using an 82599, they can have up to 64 VFs, or 63+PF, so limiting so 7 in that case is a major reduction in capability. What might work there is querying the max number of VFs and limiting to max - 1.
However, even with that, I would suggest that any limit should be possible to override. It's entirely possible that someone max actually want to reserve the full number of VFs, either because they don't want to use the NIC on the host at all, or because they are happy to use a VF on the host instead. Module parameter to allow override might work - and information on it could be added to the error message when we limit the VFs inside the driver.

/Bruce