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

[Chao Gao <chao.gao@xxxxxxxxx>]

On Tue, Apr 18, 2017 at 02:13:36AM -0600, Jan Beulich wrote:
>>>> On 16.04.17 at 22:13, <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.
>> This method will pose a strict restriction to the maximum of entry in
>> one list. But it may affect vCPU hotplug. 
>
>I don't view this as really suitable - irq_guest_action is quite different,
>as one can reasonably place expectations on how many devices may
>share an interrupt line. If someone really hit this boundary, (s)he
>could likely re-configure their system by moving expansion cards
>between slots. Neither of this is comparable with the PI situation, as
>it looks to me.
>
>Furthermore, whether a guest would be able to start / use PI would
>be quite hard to tell for an admin as it seems, again as opposed to
>the case with the shared interrupt lines.
>

Indeed. It would annoy the admin. What's your opinion on the
first and second methods? Do you think we need such policy to
restrict the #entry in the list even with the first two methods?

Thanks
Chao

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