Re: [PATCH for-6.2 v4 02/14] machine: Uniformly use maxcpus to calculate the omitted parameters

[Pankaj Gupta]

> We are currently using maxcpus to calculate the omitted sockets
> but using cpus to calculate the omitted cores/threads. This makes
> cmdlines like:
>   -smp cpus=8,maxcpus=16
>   -smp cpus=8,cores=4,maxcpus=16
>   -smp cpus=8,threads=2,maxcpus=16
> work fine but the ones like:
>   -smp cpus=8,sockets=2,maxcpus=16
>   -smp cpus=8,sockets=2,cores=4,maxcpus=16
>   -smp cpus=8,sockets=2,threads=2,maxcpus=16
> break the sanity check.
>
> Since we require for a valid config that the product of "sockets * cores
> * threads" should equal to the maxcpus, we should uniformly use maxcpus
> to calculate their omitted values.
>
> Also the if-branch of "cpus == 0 || sockets == 0" was split into two
> branches of "cpus == 0" and "sockets == 0" so that we can clearly read
> that we are parsing the configuration with a preference on cpus over
> sockets over cores over threads.
>
> Note: change in this patch won't affect any existing working cmdlines
> but improves consistency and allows more incomplete configs to be valid.
>
> Reviewed-by: Andrew Jones <drjones@redhat.com>
> Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
> ---
>  hw/core/machine.c | 30 +++++++++++++++---------------
>  hw/i386/pc.c      | 30 +++++++++++++++---------------
>  2 files changed, 30 insertions(+), 30 deletions(-)
>
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index 696d9e8e47..69979c93dd 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -755,24 +755,26 @@ static void smp_parse(MachineState *ms, 
> SMPConfiguration *config, Error **errp)
>      }
>
>      /* compute missing values, prefer sockets over cores over threads */
> -    if (cpus == 0 || sockets == 0) {
> +    maxcpus = maxcpus > 0 ? maxcpus : cpus;
> +
> +    if (cpus == 0) {
> +        sockets = sockets > 0 ? sockets : 1;
>          cores = cores > 0 ? cores : 1;
>          threads = threads > 0 ? threads : 1;
> -        if (cpus == 0) {
> -            sockets = sockets > 0 ? sockets : 1;
> -            cpus = cores * threads * sockets;
> -        } else {
> -            maxcpus = maxcpus > 0 ? maxcpus : cpus;
> -            sockets = maxcpus / (cores * threads);
> -        }
> +        cpus = sockets * cores * threads;
> +        maxcpus = maxcpus > 0 ? maxcpus : cpus;
> +    } else if (sockets == 0) {
> +        cores = cores > 0 ? cores : 1;
> +        threads = threads > 0 ? threads : 1;
> +        sockets = maxcpus / (cores * threads);
>      } else if (cores == 0) {
>          threads = threads > 0 ? threads : 1;
> -        cores = cpus / (sockets * threads);
> -        cores = cores > 0 ? cores : 1;
> +        cores = maxcpus / (sockets * threads);
>      } else if (threads == 0) {
> -        threads = cpus / (cores * sockets);
> -        threads = threads > 0 ? threads : 1;
> -    } else if (sockets * cores * threads < cpus) {
> +        threads = maxcpus / (sockets * cores);
> +    }
> +
> +    if (sockets * cores * threads < cpus) {
>          error_setg(errp, "cpu topology: "
>                     "sockets (%u) * cores (%u) * threads (%u) < "
>                     "smp_cpus (%u)",
> @@ -780,8 +782,6 @@ static void smp_parse(MachineState *ms, SMPConfiguration 
> *config, Error **errp)
>          return;
>      }
>
> -    maxcpus = maxcpus > 0 ? maxcpus : cpus;
> -
>      if (maxcpus < cpus) {
>          error_setg(errp, "maxcpus must be equal to or greater than smp");
>          return;
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index acd31af452..a9ff9ef52c 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -725,24 +725,26 @@ static void pc_smp_parse(MachineState *ms, 
> SMPConfiguration *config, Error **err
>      dies = dies > 0 ? dies : 1;
>
>      /* compute missing values, prefer sockets over cores over threads */
> -    if (cpus == 0 || sockets == 0) {
> +    maxcpus = maxcpus > 0 ? maxcpus : cpus;
> +
> +    if (cpus == 0) {
> +        sockets = sockets > 0 ? sockets : 1;
>          cores = cores > 0 ? cores : 1;
>          threads = threads > 0 ? threads : 1;
> -        if (cpus == 0) {
> -            sockets = sockets > 0 ? sockets : 1;
> -            cpus = cores * threads * dies * sockets;
> -        } else {
> -            maxcpus = maxcpus > 0 ? maxcpus : cpus;
> -            sockets = maxcpus / (dies * cores * threads);
> -        }
> +        cpus = sockets * dies * cores * threads;
> +        maxcpus = maxcpus > 0 ? maxcpus : cpus;
> +    } else if (sockets == 0) {
> +        cores = cores > 0 ? cores : 1;
> +        threads = threads > 0 ? threads : 1;
> +        sockets = maxcpus / (dies * cores * threads);
>      } else if (cores == 0) {
>          threads = threads > 0 ? threads : 1;
> -        cores = cpus / (sockets * dies * threads);
> -        cores = cores > 0 ? cores : 1;
> +        cores = maxcpus / (sockets * dies * threads);
>      } else if (threads == 0) {
> -        threads = cpus / (cores * dies * sockets);
> -        threads = threads > 0 ? threads : 1;
> -    } else if (sockets * dies * cores * threads < cpus) {
> +        threads = maxcpus / (sockets * dies * cores);
> +    }
> +
> +    if (sockets * dies * cores * threads < cpus) {
>          error_setg(errp, "cpu topology: "
>                     "sockets (%u) * dies (%u) * cores (%u) * threads (%u) < "
>                     "smp_cpus (%u)",
> @@ -750,8 +752,6 @@ static void pc_smp_parse(MachineState *ms, 
> SMPConfiguration *config, Error **err
>          return;
>      }
>
> -    maxcpus = maxcpus > 0 ? maxcpus : cpus;
> -
>      if (maxcpus < cpus) {
>          error_setg(errp, "maxcpus must be equal to or greater than smp");
>          return;

Reviewed-by: Pankaj Gupta <pankaj.gupta@ionos.com>