Re: [PATCH v2 2/2] x86: Raise the hard VCPU count limit

Ingo Molnar
2011-07-21T09:25:08Z

* Sasha Levin <levinsasha928@gmail.com> wrote:

> The patch raises the hard limit of VCPU count to 254.
>
> This will allow developers to easily work on scalability
> and will allow users to test high VCPU setups easily without
> patching the kernel.
>
> To prevent possible issues with current setups, KVM_CAP_NR_VCPUS
> now returns the recommended VCPU limit (which is still 64) - this
> should be a safe value for everybody, while a new KVM_CAP_MAX_VCPUS
> returns the hard limit which is now 254.
>
> Cc: Avi Kivity <avi@redhat.com>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Marcelo Tosatti <mtosatti@redhat.com>
> Cc: Pekka Enberg <penberg@kernel.org>
> Suggested-by: Pekka Enberg <penberg@cs.helsinki.fi>
> Signed-off-by: Sasha Levin <levinsasha928@gmail.com>

It would be nice to document the various internal limits that are
present (255, etc.) and which prevent further raising of
KVM_MAX_VCPUS.

This information got mapped out in this discussion, but the commit
loses it so it would be nice to preserve it somewhere (at least in
the changelog).

Thanks,

Ingo