RE: [RFC PATCH v3 4/4] hw/arm/virt: Parse -smp cluster parameter in virt_smp_parse

[Salil Mehta]

> From: Qemu-devel
> [mailto:qemu-devel-bounces+salil.mehta=huawei.com@nongnu.org] On Behalf Of
> Yanan Wang
> Sent: Sunday, May 16, 2021 11:32 AM
> To: Peter Maydell <peter.maydell@linaro.org>; Paolo Bonzini
> <pbonzini@redhat.com>; Andrew Jones <drjones@redhat.com>; Michael S . Tsirkin
> <mst@redhat.com>; Igor Mammedov <imammedo@redhat.com>; Shannon Zhao
> <shannon.zhaosl@gmail.com>; qemu-devel@nongnu.org; qemu-arm@nongnu.org
> Cc: Song Bao Hua (Barry Song) <song.bao.hua@hisilicon.com>; Philippe
> Mathieu-Daudé <philmd@redhat.com>; wangyanan (Y) <wangyanan55@huawei.com>;
> Zengtao (B) <prime.zeng@hisilicon.com>; Wanghaibin (D)
> <wanghaibin.wang@huawei.com>; yuzenghui <yuzenghui@huawei.com>; yangyicong
> <yangyicong@huawei.com>; zhukeqian <zhukeqian1@huawei.com>
> Subject: [RFC PATCH v3 4/4] hw/arm/virt: Parse -smp cluster parameter in
> virt_smp_parse
> 
> There is a separate function virt_smp_parse() in hw/virt/arm.c used
> to parse cpu topology for the ARM machines. So add parsing of -smp
> cluster parameter in it, then total number of logical cpus will be
> calculated like: max_cpus = sockets * clusters * cores * threads.
> 
> Note, we will assume multi-cluster in one socket is not supported
> and default the value of clusters to 1, if it's not explicitly
> specified in -smp cmdline.
> 
> Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
> ---
>  hw/arm/virt.c | 32 ++++++++++++++++++--------------
>  1 file changed, 18 insertions(+), 14 deletions(-)
> 
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index 7de822e491..678d5ef36c 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -2642,8 +2642,8 @@ static int virt_kvm_type(MachineState *ms, const char
> *type_str)
>   * with the -smp cmdlines when parsing them.
>   *
>   * We require that at least one of cpus or maxcpus must be provided.
> - * Threads will default to 1 if not provided. Sockets and cores must
> - * be either both provided or both not.
> + * Clusters and threads will default to 1 if they are not provided.
> + * Sockets and cores must be either both provided or both not.
>   *
>   * Note, if neither sockets nor cores are specified, we will calculate
>   * all the missing values just like smp_parse() does, but will disable
> @@ -2652,15 +2652,18 @@ static int virt_kvm_type(MachineState *ms, const char
> *type_str)
>  static void virt_smp_parse(MachineState *ms, QemuOpts *opts)
>  {
>      VirtMachineClass *vmc = VIRT_MACHINE_GET_CLASS(ms);
> +    VirtMachineState *vms = VIRT_MACHINE(ms);
> 
>      if (opts) {
>          unsigned cpus = qemu_opt_get_number(opts, "cpus", 0);
>          unsigned maxcpus = qemu_opt_get_number(opts, "maxcpus", 0);
>          unsigned sockets = qemu_opt_get_number(opts, "sockets", 0);
> +        unsigned clusters = qemu_opt_get_number(opts, "clusters", 0);
>          unsigned cores = qemu_opt_get_number(opts, "cores", 0);
>          unsigned threads = qemu_opt_get_number(opts, "threads", 0);
> 
> -        /* Default threads to 1 if not provided */
> +        /* Default clusters and threads to 1 if not provided */
> +        clusters = clusters > 0 ? clusters : 1;
>          threads = threads > 0 ? threads : 1;
> 
>          if (cpus == 0 && maxcpus == 0) {
> @@ -2676,13 +2679,13 @@ static void virt_smp_parse(MachineState *ms, QemuOpts
> *opts)
>              cores = 1;
>              if (cpus == 0) {
>                  sockets = 1;
> -                cpus = sockets * cores * threads;
> +                cpus = sockets * clusters * cores * threads;
>              } else {
>                  maxcpus = maxcpus > 0 ? maxcpus : cpus;
> -                sockets = maxcpus / (cores * threads);
> +                sockets = maxcpus / (clusters * cores * threads);
>              }
>          } else if (sockets > 0 && cores > 0) {
> -            cpus = cpus > 0 ? cpus : sockets * cores * threads;
> +            cpus = cpus > 0 ? cpus : sockets * clusters * cores * threads;
>              maxcpus = maxcpus > 0 ? maxcpus : cpus;
>          } else {
>              error_report("sockets and cores must be both provided "
> @@ -2695,25 +2698,26 @@ static void virt_smp_parse(MachineState *ms, QemuOpts
> *opts)
>              exit(1);
>          }
> 
> -        if (sockets * cores * threads < cpus) {
> +        if (sockets * clusters * cores * threads < cpus) {
>              error_report("cpu topology: "
> -                         "sockets (%u) * cores (%u) * threads (%u) < "
> -                         "smp_cpus (%u)",
> -                         sockets, cores, threads, cpus);
> +                         "sockets (%u) * clusters (%u) * cores (%u) * "
> +                         "threads (%u) < smp_cpus (%u)",
> +                         sockets, clusters, cores, threads, cpus);
>              exit(1);
>          }
> 
> -        if (sockets * cores * threads != maxcpus) {
> +        if (sockets * clusters * cores * threads != maxcpus) {
>              error_report("cpu topology: "
> -                         "sockets (%u) * cores (%u) * threads (%u) "
> -                         "!= maxcpus (%u)",
> -                         sockets, cores, threads, maxcpus);
> +                         "sockets (%u) * clusters (%u) * cores (%u) * "
> +                         "threads (%u) != maxcpus (%u)",
> +                         sockets, clusters, cores, threads, maxcpus);
>              exit(1);
>          }
> 
>          ms->smp.cpus = cpus;
>          ms->smp.max_cpus = maxcpus;
>          ms->smp.sockets = sockets;
> +        vms->smp_clusters = clusters;


This variable naming *smp_clusters* looks out-of-sorts. I thought a similar
variable *smp_cpus* was destined to be removed for the reason given in below
link - a patch by Andrew Jones?

Link: https://lists.gnu.org/archive/html/qemu-arm/2020-12/msg00418.html

Am I missing anything here?

Salil.

>          ms->smp.cores = cores;
>          ms->smp.threads = threads;
>      }