Re: [Xen-devel] Enabling VT-d PI by default

[Chao Gao <chao.gao@xxxxxxxxx>]

On Tue, Apr 18, 2017 at 02:24:05PM +0800, Tian, Kevin wrote:
>> From: Gao, Chao
>> Sent: Monday, April 17, 2017 4:14 AM
>> 
>> On Tue, Apr 11, 2017 at 02:21:07AM -0600, Jan Beulich wrote:
>> >>>> On 11.04.17 at 02:59, <chao.gao@xxxxxxxxx> wrote:
>> 3. Like what we do in struct irq_guest_action_t, can we limit the
>> maximum of entry we support in the list. With this approach, during
>> domain creation, we calculate the available entries and compare with
>> the domain's vCPU number to decide whether the domain can use VT-d PI.
>
>VT-d PI is global instead of per-domain. I guess you actually mean
>failing device assignment operation if counting new domain's #VCPUs
>exceeds the limitation.

Almost agree. But I think device assignment is also allowed in that
case.  We just disable the new created domain to use VT-d PI.

>
>> This method will pose a strict restriction to the maximum of entry in
>> one list. But it may affect vCPU hotplug.
>> 
>> According to your intuition, which methods are feasible and
>> acceptable? I will attempt to mitigate this issue per your advices.
>> 
>
>My understanding is that we need them all. #1 is the baseline,
>with #2/#3 as further optimization. :-)

Thanks your input. I will have a try.

Thanks
Chao

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