[bhyve][arm64] Number of allowed vcpus

[Rodney W. Grimes]

> On Wed, Jan 13, 2021 at 4:55 PM Rodney W. Grimes <
> freebsd-rwg at gndrsh.dnsmgr.net> wrote:
> 
> > > Hello,
> > >
> > > >From my perspective bhyve should use what is stated in the device tree
> > if
> > > no parameter is given and throw an error when N is greater than the
> > device
> > > tree value.
> > >
> > > Mihai
> >
> > That seems to be one reasonable solution.  I am not very informed on what
> > the CPU over commit situation is on an ARM cpu with respect to
> > virtualization.
> >
> > I would also propose as an alternative to just do what was asked by the
> > user, which is the current amd64 implementation, OR do as asked and
> > emmit a warning message.
> >
> > I would ask given what was said above: isnt this the same situation as
> > if the sum of all VM VCPU's is more than the total cores in the system?
> > That is a very common situation, and one we must not restrict.
> >
> 
> We are talking here about the device tree of the guest. If you boot up a
> guest with a device tree of X vcpus, why specify something else on the
> command line?

Oh, that is/was not clear from the original post, it did not specify
which device tree was being discussed.  How do we even see the guest
device tree (again, pointing to my lack of knowledge on the ARM bhyve
implementation.)

Also would this not be about the same as taking my flash card out of
a 4 CPU system and plugging it into a 8 CPU system without updating
the device tree?  What would real hardware do here?

> > > On Wed, Jan 13, 2021 at 1:55 PM Andrei Martin <
> > andrei.cos.martin at gmail.com>
> > > wrote:
> > >
> > > > Hello,
> > > >
> > > > While working on enabling multiple virtual cpus for the arm64 virtual
> > > > machine
> > > > I used the bhyve's "-c N" parameter to create N cpus (it gets only the
> > > > cpus, in contrast to the amd64). If N is smaller than the number of
> > cores
> > > > described in the device tree it will enable only N and if it's larger
> > it
> > > > will enable only the number of cores from the device tree.
> > > >
> > > > I don't know if it is the best approach. Another way would be to enable
> > > > all the cpus from the device tree, no more, no less.
> > > >
> > > > Do you have any suggestions?
> > > >
> > > > Andrei
> > > >
> > > _______________________________________________
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> > >
> >
> > --
> > Rod Grimes
> > rgrimes at freebsd.org
> >

-- 
Rod Grimes                                                 rgrimes at freebsd.org