Re: [xen-4.12-testing test] 169199: regressions - FAIL

[Jan Beulich <jbeulich@suse.com>]

On 08.04.2022 13:16, Roger Pau Monné wrote:
> On Fri, Apr 08, 2022 at 12:08:02PM +0100, Julien Grall wrote:
>> On 08/04/2022 12:01, Roger Pau Monné wrote:
>>>>> I could add a suitable dom0_max_vcpus parameter to osstest.  XenServer
>>>>> uses 16 for example.
>>>>
>>>> I'm afraid a fixed number won't do, the more that iirc there are
>>>> systems with just a few cores in the pool (and you don't want to
>>>> over-commit by default).
>>>
>>> But this won't over commit, it would just assign dom0 16 vCPUs at
>>> most, if the system has less than 16 vCPUs that's what would be
>>> assigned to dom0.
>>
>> AFAICT, this is not the case on Arm. If you ask 16 vCPUs, then you will get
>> that number even if there are 8 pCPUs.
>>
>> In fact, the documentation of dom0_max_vcpus suggests that the numbers of
>> vCPUs can be more than the number of pCPUs.
> 
> It was my understanding that you could only achieve that by using the
> min-max nomenclature, so in order to force 16 vCPUs always you would
> have to use:
> 
> dom0_max_vcpus=16-16
> 
> Otherwise the usage of '_max_' in the option name is pointless, and it
> should instead be dom0_vcpus.

I disagree: Unlike for DomU there's no way to keep a "reserve" of vCPU-s
for Dom0, except by offlining some once Dom0 runs. Hence this "max" in
the name is quite applicable.

Jan