Re: [PATCH v11 01/14] machine: Deprecate "parameter=0" SMP configurations

[Daniel P . Berrangé]

On Tue, Sep 28, 2021 at 11:57:42AM +0800, Yanan Wang wrote:
> In the SMP configuration, we should either provide a topology
> parameter with a reasonable value (greater than zero) or just
> omit it and QEMU will compute the missing value.
> 
> The users shouldn't provide a configuration with any parameter
> of it specified as zero (e.g. -smp 8,sockets=0) which could
> possibly cause unexpected results in the -smp parsing. So we
> deprecate this kind of configurations since 6.2 by adding the
> explicit sanity check.
> 
> Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
> ---
>  docs/about/deprecated.rst | 15 +++++++++++++++
>  hw/core/machine.c         | 14 ++++++++++++++
>  qapi/machine.json         |  2 +-
>  qemu-options.hx           | 12 +++++++-----
>  4 files changed, 37 insertions(+), 6 deletions(-)
> 
> diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
> index 3c2be84d80..97415dbecd 100644
> --- a/docs/about/deprecated.rst
> +++ b/docs/about/deprecated.rst
> @@ -160,6 +160,21 @@ Use ``-display sdl`` instead.
>  
>  Use ``-display curses`` instead.
>  
> +``-smp`` ("parameter=0" SMP configurations) (since 6.2)
> +'''''''''''''''''''''''''''''''''''''''''''''''''''''''
> +
> +Specified CPU topology parameters must be greater than zero.
> +
> +In the SMP configuration, users should either provide a CPU topology
> +parameter with a reasonable value (greater than zero) or just omit it
> +and QEMU will compute the missing value.
> +
> +However, historically it was implicitly allowed for users to provide
> +a parameter with zero value, which is meaningless and could also possibly
> +cause unexpected results in the -smp parsing. So support for this kind of
> +configurations (e.g. -smp 8,sockets=0) is deprecated since 6.2 and will
> +be removed in the near future, users have to ensure that all the topology
> +members described with -smp are greater than zero.
>  
>  Plugin argument passing through ``arg=<string>`` (since 6.1)
>  ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index 067f42b528..711e83db54 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -835,6 +835,20 @@ static void machine_set_smp(Object *obj, Visitor *v, 
> const char *name,
>          return;
>      }
>  
> +    /*
> +     * Specified CPU topology parameters must be greater than zero,
> +     * explicit configuration like "cpus=0" is not allowed.
> +     */
> +    if ((config->has_cpus && config->cpus == 0) ||
> +        (config->has_sockets && config->sockets == 0) ||
> +        (config->has_dies && config->dies == 0) ||
> +        (config->has_cores && config->cores == 0) ||
> +        (config->has_threads && config->threads == 0) ||
> +        (config->has_maxcpus && config->maxcpus == 0)) {
> +        warn_report("Invalid CPU topology deprecated: "
> +                    "CPU topology parameters must be greater than zero");
> +    }
> +
>      mc->smp_parse(ms, config, errp);
>      if (*errp) {
>          goto out_free;
> diff --git a/qapi/machine.json b/qapi/machine.json
> index 32d47f4e35..227e75d8af 100644
> --- a/qapi/machine.json
> +++ b/qapi/machine.json
> @@ -1331,7 +1331,7 @@
>  #
>  # @dies: number of dies per socket in the CPU topology
>  #
> -# @cores: number of cores per thread in the CPU topology
> +# @cores: number of cores per die in the CPU topology
>  #
>  # @threads: number of threads per core in the CPU topology
>  #

This change is unrelated to the rest of this commit.

It just looks like a simple bug fix and should just be
spun out into its own patch.

> diff --git a/qemu-options.hx b/qemu-options.hx
> index 8f603cc7e6..91d859aa29 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -227,11 +227,13 @@ SRST
>      of computing the CPU maximum count.
>  
>      Either the initial CPU count, or at least one of the topology parameters
> -    must be specified. Values for any omitted parameters will be computed
> -    from those which are given. Historically preference was given to the
> -    coarsest topology parameters when computing missing values (ie sockets
> -    preferred over cores, which were preferred over threads), however, this
> -    behaviour is considered liable to change.
> +    must be specified. The specified parameters must be greater than zero,
> +    explicit configuration like "cpus=0" is not allowed. Values for any
> +    omitted parameters will be computed from those which are given.
> +    Historically preference was given to the coarsest topology parameters
> +    when computing missing values (ie sockets preferred over cores, which
> +    were preferred over threads), however, this behaviour is considered
> +    liable to change.
>  ERST
>  
>  DEF("numa", HAS_ARG, QEMU_OPTION_numa,

If you split the docs fix out into its own patch then you can add

  Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

to both this patch and the new patch.

Regards,
Daniel
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