[ipxe-devel] hyperv net device driver design question

[Michael Brown]

On 22/01/18 17:12, Roman Kagan wrote:
> Our workaround was to disable the message page once the VMBus setup was
> over and the message page was no longer needed, and not to enable the
> event page as we were using polling anyway so we could busy-wait
> directly on the ringbuffer descriptors.

That didn't seem to work for us; the virtual NIC stopped passing traffic 
as soon as Windows took ownership of VMBus.

>> I'd be very happy to update iPXE to bind via the VMBus UEFI protocols, if
>> you have documentation and/or an open source implementation of the protocols
>> matching those found in Hyper-V's own UEFI firmware.
> 
> Frankly I think Microsoft has no incentive to even make this protocol
> stable, let alone document it, so I don't see this as a viable solution.

Fair point.

> OTOH we already have a preliminary version of Hyper-V SCSI driver for
> OVMF; it also includes the VMBus bus driver defining its own protocol
> (similar to XenBus) to which the devices attach.  I guess iPXE can be
> made to use it if found in the system.

That sounds like a good plan to me.

>  What is unclear to me is whether
> it's beneficial compared to re-implementing the Hyper-V network driver
> in OVMF proper, given that OVMF has a fairly complete network stack
> itself and that it's not quite obvious how to make iPXE available in
> OVMF.

The network stack in EDK2 (and hence OVMF) is nowhere near as fast as 
iPXE.  I've personally observed iPXE obtain sustained throughputs of 
5000 Mbps; the EDK2 stack typically struggles to reach even 100 Mbps. 
Also, we have meaningful error messages.  :)

If there's going to be a stable (and, ideally, documented) protocol for 
VMBus in OVMF, then I'll be updating iPXE to be able to use it anyway. 
Is the protocol header file available somewhere?

Thanks,

Michael