Re: [RFC PATCH v2 2/4] hw/arm/virt: Parse -smp cluster parameter in virt_smp_parse

[Andrew Jones <drjones@redhat.com>]

On Fri, Apr 30, 2021 at 08:41:25AM +0200, Andrew Jones wrote:
> On Fri, Apr 30, 2021 at 01:09:00PM +0800, wangyanan (Y) wrote:
> > But I think the requirement for ARM "if even one parameter other than cpus
> > or maxcpus
> > is provided then all parameters must be provided" will be better. This can
> > ensure the
> > whole accurate users-specified topology. As you mentioned, if anybody who
> > bothers
> > to specify one, why not also specify the others.
> > 
> > I can add the requirement for ARM in the documentation, and also check the
> > parameters
> > in virt_smp_parse. Will this be fine?
> 
> We sort of have to support command lines that are missing 'maxcpus' and
> 'clusters', unless we work together with libvirt to make the change.
> Currently libvirt will generate '-smp 16,sockets=16,cores=1,threads=1'
> from '<vcpu placement='static'>16</vcpu>'. That's sufficient for our
> stricter, but not completely strict requirements. And, I still think
> 'threads' could be optional, because there's a good chance the user
> doesn't want to describe them, so a default of 1 is good enough. Also,
> given maxcpus, but not cpus, it's pretty obvious that cpus should equal
> maxcpus.
>

We also still need just 'cpus' or just 'maxcpus' to work, since that
already works now. So, at least these should work

 -smp N
 -smp maxcpus=N
 -smp N,maxcpus=M
 -smp N,sockets=N,cores=1,threads=1
 -smp N,maxcpus=M,sockets=M,cores=1,threads=1

since they work today, even though no topology is described. If we want to
describe a topology for the first three, then we'll have to pick one,
which brings us back to the sockets over cores stuff. Or, we could choose
to just not generate topology descriptions when none is provided.

Thanks,
drew