Re: [Qemu-devel] [PULL 02/45] vl.c deprecate incorrect CPUs topology

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Oct 18, 2018 at 05:03:39PM -0300, Eduardo Habkost wrote:
> From: Igor Mammedov <imammedo@redhat.com>
> 
> -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: Igor Mammedov <imammedo@redhat.com>
> Reviewed-by: Andrew Jones <drjones@redhat.com>
> Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
> Message-Id: <1536836762-273036-2-git-send-email-imammedo@redhat.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  vl.c                 |  7 +++++++
>  qemu-deprecated.texi | 12 ++++++++++++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/vl.c b/vl.c
> index 4e25c78bff..027d04c7ca 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -1235,6 +1235,13 @@ static void smp_parse(QemuOpts *opts)
>              exit(1);
>          }
>  
> +        if (sockets * cores * threads != max_cpus) {
> +            warn_report("Invalid CPU topology deprecated: "
> +                        "sockets (%u) * cores (%u) * threads (%u) "
> +                        "!= maxcpus (%u)",
> +                        sockets, cores, threads, max_cpus);
> +        }
> +
>          smp_cpus = cpus;
>          smp_cores = cores;
>          smp_threads = threads;
> diff --git a/qemu-deprecated.texi b/qemu-deprecated.texi
> index 11b870c5c1..5d2d7a3588 100644
> --- a/qemu-deprecated.texi
> +++ b/qemu-deprecated.texi
> @@ -86,6 +86,18 @@ for these file types is 'host_cdrom' or 'host_device' as appropriate.
>  The @option{name} parameter of the @option{-net} option is a synonym
>  for the @option{id} parameter, which should now be used instead.
>  
> +@subsection -smp (invalid topologies) (since 3.1)
> +
> +CPU topology properties should describe whole machine topology including
> +possible CPUs.
> +
> +However, historically it was possible to start QEMU with an incorrect topology
> +where @math{@var{n} <= @var{sockets} * @var{cores} * @var{threads} < @var{maxcpus}},
> +which could lead to an incorrect topology enumeration by the guest.
> +Support for invalid topologies will be removed, the user must ensure
> +topologies described with -smp include all possible cpus, i.e.
> +  @math{@var{sockets} * @var{cores} * @var{threads} = @var{maxcpus}}.
> +
>  @section QEMU Machine Protocol (QMP) commands
>  
>  @subsection block-dirty-bitmap-add "autoload" parameter (since 2.12.0)

-- 
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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