Re: Xen/arm: Virtual ITS command queue handling

[Vijay Kilari <vijay.kilari@gmail.com>]

On Tue, May 19, 2015 at 7:24 PM, Ian Campbell <ian.campbell@citrix.com> wrote:
> On Tue, 2015-05-19 at 14:36 +0100, Ian Campbell wrote:
>> On Tue, 2015-05-19 at 14:27 +0100, Julien Grall wrote:
>> > With the multiple vITS we would have to retrieve the number of vITS.
>> > Maybe by extending the xen_arch_domainconfig?
>>
>> I'm sure we can find a way.
>>
>> The important question is whether we want to go for a N:N vits:pits
>> mapping or 1:N.
>>
>> So far I think we are leaning (slightly?) towards the 1:N model, if we
>> can come up with a satisfactory answer for what to do with global
>> commands.
>
> Actually, Julien just mentioned NUMA which I think is a strong argument
> for the N:N model.
>
> We need to make a choice here one way or another, since it has knock on
> effects on other parts, e.g the handling of SYNC and INVALL etc.
>
> Given that N:N seems likely to be simpler from the Xen side and in any
> case doesn't preclude us moving to a 1:N model (or even a 2:N model etc)
> in the future how about we start with that?
>
> If there is agreement in taking this direction then I will adjust the
> relevant sections of the document to reflect this.

Yes, this make Xen side simple. Most important point to discuss is

1) How Xen maps vITS to pITS. its0 -> vits0?
2) When PCI device is assigned to DomU, how does domU choose
    vITS to send commands.  AFAIK, the BDF of assigned device
    is different from actual BDF in DomU.