Re: [dpdk-dev] [RFC] ethdev: use special speed for virtual Ethernetdevices

["Morten Brørup" <mb@smartsharesystems.com>]

> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Thomas Monjalon
> Sent: Wednesday, April 1, 2020 11:54 AM
> 
> 01/04/2020 11:33, Morten Brørup:
> > Thomas, Ferruh, Andrew (Ethernet API Maintainers),
> >
> > A command line option was recently added to set which speed a vNIC
> reports when the link is up. This makes sense for Spanning Tree and
> other protocols which depend on link speed.
> 
> Please could you reference the patch?

It is a patch for the virtio driver:
http://inbox.dpdk.org/dev/20191212085012.9170-1-i.dyukov@samsung.com/T/#m052f90ea8c559406aeaefaea1fc24ed9bb573788

> 
> > However, I suspect that this workaround rarely reflects the physical
> truth, and suggest that the application should handle it instead.
> 
> I don't understand why we need to define some speed for virtual
> devices.
> 
> > In other words... Instead of faking it in the virtual Ethernet
> drivers, I suggest that rte_ethdev.h defines a special speed value for
> vNICs which really don't have a physical link speed:
> >
> > #define ETH_SPEED_NUM_NONE         0 /**< Not defined */
> 
> The only issue with this constant is the lack of RTE_ prefix :-)
> Otherwise I think "0 - NONE - not defined" fits well with virtual
> device case.
> 
> > +#define ETH_SPEED_NUM_UNKNOWN      1 /**< Unknown (virtual device)
> */
> 
> 1 means 1 Mbps
> 
> > #define ETH_SPEED_NUM_10M         10 /**<  10 Mbps */
> >
> > Alternatively, we could expand the meaning of ETH_SPEED_NUM_NONE:
> >
> > -#define ETH_SPEED_NUM_NONE         0 /**< Not defined */
> > +#define ETH_SPEED_NUM_NONE         0 /**< Not defined or unknown
> (virtual device) */
> 
> Yes I agree with extending the comment for NONE.
> 
> > The special value could also be used in cases like this:
> >
> http://inbox.dpdk.org/dev/AM0PR0502MB401907ADE7CEA27DC642DF35D2CB0@AM0P
> R0502MB4019.eurprd05.prod.outlook.com/T/#t
> 
> Yes, if speed is unknown, it should be reported as 0.

So the next related question is: Should a vNIC be allowed to report a fake speed if it does not know that the underlying hardware actually provides this speed?