Re: [Xen-devel] Status of FLR in Xen 4.4

[Matthias <matthias.kannenberg@xxxxxxxxxxxxxx>]

Hi,

thanks for your answers, the cards are a AMD HD 5750 and a HD 5400, both with dual functions (due to audio capabilities), both co-assigned to their respective domU and both not capable of FLR from lspci -vvv output.

also, @Ross, I'm running a 3.8.2 Kernel, so this should be fine, but I assume that the 'official' command where xl asks the dom0 about the reset do not work (if I have understand david correctly) since it's dual function so no dual bus reset is actually executed causing the misbehaviour, and on the other side xm doing a bus reset so it works in this specific case.

I'm currently recompiling the kernel to see if your patch works David.

Also, just to understand it better, is the secondary bus reset the thing which you can manually invoke via /sys/bus/pci/devices/.../reset ?

So as a workaround, would the following work in principle?

xl pci-assignable-remove 0X:00.0
xl pci-assignable-remove 0X:00.1

echo "1" > /sys/bus/pci/devices/0X:00.0/reset
echo "1" > /sys/bus/pci/devices/0X:00.1/reset
xl pci-assignable-add 0X:00.0
xl pci-assignable-add 0X:00.1

Anyway, thanks for your answers and I will report if the patch works!

2013/9/26 David Vrabel <david.vrabel@xxxxxxxxxx>

On 26/09/13 18:48, Ross Philipson wrote:
> On 09/26/2013 12:20 PM, David Vrabel wrote:
>> On 26/09/13 17:05, Matthias wrote:
>>> Hi everyone,
>>>
>>> I would like to ask what the current status of FLR, or better of FLR
>>> emulation is in latest Xen and if we can expect better support in the
>>> future.
>>
>> What are these cards, are they multi-function and do they actually
>> support FLR?  Many graphics cards do not.
>>
>> I have the following hack to pciback to fallback to a bus reset for
>> multi-function devices without FLR.  Does it help for your use case?
>> You will need to ensure that all functions are co-assigned to the same
>> domain.
>
> New kernels (e.g. 3.8) have full support for PCI-e and PCI AF FLRs as
> well as fallback support for D0-D3 and secondary bus resets. This
> functionality is also in the some of the last 2.6 kernels like 2.6.39.
> If you are using an older kernel I guess you might need to patch it.

It will only do a secondary bus reset iff the function to be reset is
the only function on that bus.  If you have a multi-function device
secondary bus reset is not tried.

David

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