Re: [Xen-users] How to assign a SR-IOV Virtual Function to Host

[Mark van Dijk <lists+xen@xxxxxxxxxxxxxx>]

>I have a use-case like, I need to use one of the VFs on the host
>machine itself.
>So, is there any way to assign VF to host itself and use it as a
>regular device there.
>
>Or, how can we can access a VF created by SR-OV on host machine
>directly.

Hi Venkatesh,

I tested SR-IOV a couple of months ago and this is how I got it to work
at one point.

So, normally you have an ethernet device with address e.g. 02:00.0. With
SR-IOV the addresses are extended. From memory I recall this extends
addresses to something like either 02:00.1, 02:00.2 OR 02:01.0,
02:02.0. It's one or the other.

Then I got SR-IOV to work by issuing, in the dom0 kernel boot cmdline,
xen.pciback=(02:00.1)(02:00.2).

If you don't hide the base address (02:00.0) in that line then it
should still be usable by the dom0. And then in your VM config you pass
the address to the VM with e.g. pci=['02:00.1'].

I also found that SR-IOV degraded the performance of the NIC somewhat.

Note that SR-IOV is only supported by some devices, e.g. the Intel
10Gbit ixgbe device. I used Intel's external driver (the one they share
on their website, it is different from the in-kernel driver). Read the
README thoroughly and make sure that you disable LRO, this is crucial
for both SR-IOV and for the ip_forward=1 sysctl, even without SR-IOV.

LRO can be disabled in a couple of ways -- when you compile the module;
when you load the kernel module with LRO=0 in modules.conf or by using
ethtool. I strongly recommend you use the first option here: disable it
by passing some argument to the 'make' command -- this should be in the
README, at least for Intel drivers.

Let me know if this works for you. If not I will test this stuff out on
my SR-IOV capable server and get back to you. 

-- 
Adios,
Mark van Dijk.                ,---------------------------------
-----------------------------'         Wed Sep 05 10:43 UTC 2012
Today is Pungenday, the 29th day of Bureaucracy in the YOLD 3178

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