Re: [Qemu-arm] [PATCH RFC 06/16] vl: move smp parsing to machine pre_init

[David Gibson]

On Tue, Jun 14, 2016 at 10:17:49AM +0200, Paolo Bonzini wrote:
> 
> 
> On 13/06/2016 22:35, Andrew Jones wrote:
> > On Mon, Jun 13, 2016 at 07:04:01PM +0200, Paolo Bonzini wrote:
> >> On 10/06/2016 19:40, Andrew Jones wrote:
> >>> +    if (sockets == -1 || cores == -1 || threads == -1 ||
> >>> +        maxcpus == -1 || cpus == -1) {
> >>> +        error_report("cpu topology: "
> >>> +                     "all machine properties must be specified");
> >>> +        exit(1);
> >>> +    }
> >>> +
> >>
> >> I think it's sane to accept some defaults.  It must not be the DWIM
> >> thing that -smp does (which is targeted to Windows's dislike of
> >> multi-socket machine on consumer hardware).  It must be something that
> >> makes sense, and my proposal is:
> >>
> >> - threads: 1
> >> - cores: 1
> >> - sockets:
> >>   - maxcpus / (cores * threads) if maxcpus given
> >>   - cpus / (cores * threads) if cpus given
> >>   - else 1
> >> - maxcpus: cores * threads * sockets
> >> - cpus: maxcpus
> > 
> > I think some machines may prefer
> > 
> > - threads: 1
> > - sockets: 1
> > - cores:
> >   - maxcpus / (sockets * threads) if maxcpus given
> >   - cpus / (sockets * threads) if cpus given
> >   - else 1
> 
> smp_cores is only used by pseries and x86 machines.  I expect machines
> that must be single-socket to disregard smp_sockets altogether.

Note that on pseries (as a purely paravirt platform), the distinction
between cores and sockets is basically meaningless - there is no
important difference between a threads=4,cores=4,sockets=1 machine and
a threads=4,cores=1,sockets=4 machine.s

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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