Re: [Xen-devel] [PATCH] x86/apic/x2apic: Share IRQ vector between cluster members only when no cpumask is specified

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 08/07/2017 12:20 PM, Andrew Cooper wrote:
> On 07/08/17 17:06, Jan Beulich wrote:
>>>>> Andrew Cooper <andrew.cooper3@xxxxxxxxxx> 08/07/17 5:40 PM >>>
>>> On 07/08/17 16:38, Jan Beulich wrote:
>>>> So a single NIC drove the system out of vectors? That's insane, I would
>>>> say, i.e. I'd call this a misconfigured system. But yeah, if we really want
>>>> to get such a thing to work despite the insanity ...
>>> No.  That's one single (dual headed) card with 128 virtual functions each.
>> But putting such in a single-core system is, well, not very reasonable. At
>> the very least I'd expect the admin to limit the number of VFs then, or not
>> load a driver in Dom0 for them (but only for the PF).
> Its not a single core system, but cluster mode allocates vectors across
> clusters, not cores. This turns even the largest server system into a
> single core system as far as vector availability goes.

In my case we have enough vectors on a fully-populated system (4
sockets), which is how it was installed.

However, we want to be able to reduce the number of processors and one
such configuration is to limit processors to a single socket (which
translates to a single cluster as far APIC is concerned). Requiring
admins to also reduce number of virtual functions is probably somewhat
complicated to explain/document (especially since this would depend on
number of cores on a socket).

-boris

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