Re: [Xen-devel] Dynamically adjust nr_pirqs (aka extra_domU_irqs) from 32 default to an value based on MSI-X options, etc.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.09.15 at 15:42, <konrad.wilk@xxxxxxxxxx> wrote:
> We are running into issues where our guests immediately exhaust
> the amount of PIRQs. Using the 'extra_guest_irqs' of course fixes
> it but it would be nice to have this be dynamic.
> 
> One idea I had been toying with was that when an device is inserted
> into an domain we check how many MSI-X it could have and raise
> the nr_pirqs by that. But that would entail some extra logic in
> the libxl. And naturally an hypercall to modify the nr_pirqs.
> 
> The other is to evaluate also based on MSI-X - but in the
> hypervisor as it already has logic to do figure out MSI-X and such.
> 
> Would appreciate feedback, thoughts, etc.

Growing nr_pirqs at any point would be no problem. The issue I
see is making sure it gets shrunk back as needed. In any event
I would favor a solution inside the hypervisor over one involving
the tool stack.

Jan


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