Re: [PATCH v2] hw/i386: Expand the range of CPU topologies between smp and maxcpus

[Daniel P . Berrangé]

On Mon, Apr 26, 2021 at 10:08:52AM +0800, caodongli@kingsoft.com wrote:
> Change the criteria for the initial CPU topology and maxcpus, user can
> have more settings

Can you provide a better explanation of why this is needed. What
valid usage scenario is blocked by the current check ?

AFAICT, it partially reverts an intentional change done in several
years ago in :


  commit bc1fb850a31468ac4976f3895f01a6d981e06d0a
  Author: Igor Mammedov <imammedo@redhat.com>
  Date:   Thu Sep 13 13:06:01 2018 +0200

    vl.c deprecate incorrect CPUs topology
    
    -smp [cpus],sockets/cores/threads[,maxcpus] should describe topology
    so that total number of logical CPUs [sockets * cores * threads]
    would be equal to [maxcpus], however historically we didn't have
    such check in QEMU and it is possible to start VM with an invalid
    topology.
    Deprecate invalid options combination so we can make sure that
    the topology VM started with is always correct in the future.
    Users with an invalid sockets/cores/threads/maxcpus values should
    fix their CLI to make sure that
       [sockets * cores * threads] == [maxcpus]



> 
> Signed-off-by: Dongli Cao <caodongli@kingsoft.com>
> ---
> hw/i386/pc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index 8a84b25..ef2e819 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -751,7 +751,7 @@ void pc_smp_parse(MachineState *ms, QemuOpts *opts)
>              exit(1);
>          }
> 
> -        if (sockets * dies * cores * threads != ms->smp.max_cpus) {
> +        if (sockets * dies * cores * threads > ms->smp.max_cpus) {
>              error_report("Invalid CPU topology deprecated: "
>                           "sockets (%u) * dies (%u) * cores (%u) * threads 
> (%u) "
>                           "!= maxcpus (%u)",

This is 

> --
> 1.8.3.1
> 
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> caodongli@kingsoft.com
> 
> 

Regards,
Daniel
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