Re: [PATCH v2 1/5] hw: Add sockets_specified field in CpuTopology

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, May 27, 2020 at 11:12:22AM +0530, Anup Patel wrote:
> When "sockets" sub-option of "-smp" option is not specified, the
> smp_parse() function will assume one CPU per-socket and set the
> number of sockets equal to number of CPUs.
> 
> This is counter-intuitive and we should allow machine emulation to
> decide default number of sockets when "sockets" sub-option is not
> specified.

I don't agree with this.  Having the semantics of the -smp option
be the same across all targets/machines *is* intuitive.  Changing
semantics of -smp per-machine will create a worse experiance for
people configuring QEMU as the configuration will mean different
things depending on the machine choce.


>           To achieve this, we add boolean flag sockets_specified
> in struct CpuTopology which tells machine emulation whether the
> "sockets" sub-option was specified in command-line.
> 
> Signed-off-by: Anup Patel <anup.patel@wdc.com>
> ---
>  hw/core/machine.c   | 2 ++
>  include/hw/boards.h | 2 ++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index bb3a7b18b1..fd5ef5a4bb 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -706,6 +706,8 @@ static void smp_parse(MachineState *ms, QemuOpts *opts)
>          unsigned cores   = qemu_opt_get_number(opts, "cores", 0);
>          unsigned threads = qemu_opt_get_number(opts, "threads", 0);
>  
> +         ms->smp.sockets_specified = (sockets == 0) ? false : true;
> +
>          /* compute missing values, prefer sockets over cores over threads */
>          if (cpus == 0 || sockets == 0) {
>              cores = cores > 0 ? cores : 1;
> diff --git a/include/hw/boards.h b/include/hw/boards.h
> index 18815d9be2..59b28ada65 100644
> --- a/include/hw/boards.h
> +++ b/include/hw/boards.h
> @@ -244,6 +244,7 @@ typedef struct DeviceMemoryState {
>   * @cores: the number of cores in one package
>   * @threads: the number of threads in one core
>   * @sockets: the number of sockets on the machine
> + * @sockets_specified: the number of sockets were specified for the machine
>   * @max_cpus: the maximum number of logical processors on the machine
>   */
>  typedef struct CpuTopology {
> @@ -251,6 +252,7 @@ typedef struct CpuTopology {
>      unsigned int cores;
>      unsigned int threads;
>      unsigned int sockets;
> +    bool sockets_specified;
>      unsigned int max_cpus;
>  } CpuTopology;
>  
> -- 
> 2.25.1
> 
> 

Regards,
Daniel
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