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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Jan


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