Re: [Qemu-devel] [PATCH 15/22] machine: make max_cpus a -machine option

[Anthony Liguori]

On 06/07/2010 08:01 PM, Paul Brook wrote:
> > diff --git a/hw/realview.c b/hw/realview.c
> > index a36bdbe..8dcef80 100644
> > --- a/hw/realview.c
> > +++ b/hw/realview.c
> > @@ -444,9 +444,9 @@ static QEMUMachine realview_eb_mpcore_machine = {
> >       .init = realview_eb_mpcore_init,
> >       .opts_default = (QemuOptValue[]) {
> >           QOPT_VALUE("default_drive", "scsi"),
> > +        QOPT_VALUE("max_cpus", "4"),
> >           { /* end of list */ }
> >       },
> > -    .max_cpus = 4,
> >   };
> >      
> By my reading this allows the user to modify this value. If so it is wrong.
>    

max_cpus is complicated because it was used for multiple purposes.

I think max_cpus ought to be configurable.  The reason it's useful to 
configure it that it lets a downstream specify a recommended max cpu 
that's mostly relevant from a scalability perspective.  For instance, 
you may want to set the pc max_cpus to 64 since this is the highest that 
KVM supports today.

> This is a fundamental property/limitation of the hardware. Expect qemu to
> crash if the value is modified.
>    

In this case, the machine cores should be rejecting totally invalid 
values to prevent crashes from occurring.  My reading of realview does 
not suggest that a crash would occur.  Are you speaking in general terms 
or do you think it will actually fail in realview?

Regards,

Anthony Liguori


> Paul
>
>