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

["wangyanan (Y)" <wangyanan55@huawei.com>]

On 2021/9/28 17:58, Daniel P. Berrangé wrote:
> 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
Ok, I will split it out. Thanks for the review of this series.

Thanks,
Yanan
>
>    Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
>
> to both this patch and the new patch.
>
> Regards,
> Daniel