How hard is BHyVe's 16 vCPU limit, is it configurable under any circumstance?
tinkr at openmailbox.org
Wed Nov 12 22:09:01 UTC 2014
On 2014-11-12 23:55, Allan Jude wrote:
> On 2014-11-12 16:39, tinkr at openmailbox.org wrote:
>> In order justify giving energy to BHyVe, I need to know if it's
>> "future-proof" in that the 16 vCPU limit can be increased?
>> Please let the world know if BHyVe's 16 vCPU limit can be lifted in
>> way, by configuration, patch, etc. (and if you want to, why this limit
>> is in place by default today).
>> freebsd-virtualization at freebsd.org mailing list
>> To unsubscribe, send any mail to
>> "freebsd-virtualization-unsubscribe at freebsd.org"
> You can increase the limit by editing sys/amd64/include/vmm.h
> #define VM_MAXCPU 16
> From what I've been told, things scale badly above 24 CPUs. They plan
> solve this issue, but have not yet. If you system has enough cores to
> support using more than 16 per VM, you can modify the file and
> the kernel and use as many CPUs as you want, but not much testing has
> happened with bigger numbers.
Thank you very much for responding.
Only for completeness, do you have any particular idea about
* When the scaling above 24 vCPU:s will be optimized, like approx how
many years away is it (like 1 or more than 1)?, and
* What the technological reason for the scaling is, is it that somehow
the BHyVe instances on the different cores need to inter-communicate,
for instance that all disk and network IO is done via one single core
In all cases, your response is great news, as your baseline answer that
it's doable and only a question of optimization and tweaking of present
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