Re: [PATCH v6 1/7] hw/arm/virt: Support CPU cluster on ARM virt machine

[Andrew Jones <drjones@redhat.com>]

On Mon, Jan 03, 2022 at 04:46:30PM +0800, Yanan Wang wrote:
> ARM64 machines like Kunpeng Family Server Chips have a level
> of hardware topology in which a group of CPU cores share L3
> cache tag or L2 cache. For example, Kunpeng 920 typically
> has 6 or 8 clusters in each NUMA node (also represent range
> of CPU die), and each cluster has 4 CPU cores. All clusters
> share L3 cache data, but CPU cores in each cluster share a
> local L3 tag.
> 
> Running a guest kernel with Cluster-Aware Scheduling on the
> Hosts which have physical clusters, if we can design a vCPU
> topology with cluster level for guest kernel and then have
> a dedicated vCPU pinning, the guest will gain scheduling
> performance improvement from cache affinity of CPU cluster.
> 
> So let's enable the support for this new parameter on ARM
> virt machines. After this patch, we can define a 4-level
> CPU hierarchy like: cpus=*,maxcpus=*,sockets=*,clusters=*,
> cores=*,threads=*.
> 
> Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
> ---
>  hw/arm/virt.c   |  1 +
>  qemu-options.hx | 10 ++++++++++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index 6bce595aba..f413e146d9 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -2700,6 +2700,7 @@ static void virt_machine_class_init(ObjectClass *oc, void *data)
>      hc->unplug_request = virt_machine_device_unplug_request_cb;
>      hc->unplug = virt_machine_device_unplug_cb;
>      mc->nvdimm_supported = true;
> +    mc->smp_props.clusters_supported = true;
>      mc->auto_enable_numa_with_memhp = true;
>      mc->auto_enable_numa_with_memdev = true;
>      mc->default_ram_id = "mach-virt.ram";
> diff --git a/qemu-options.hx b/qemu-options.hx
> index fd1f8135fb..69ef1cdb85 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -277,6 +277,16 @@ SRST
>  
>          -smp 16,sockets=2,dies=2,cores=2,threads=2,maxcpus=16
>  
> +    The following sub-option defines a CPU topology hierarchy (2 sockets
> +    totally on the machine, 2 clusters per socket, 2 cores per cluster,
> +    2 threads per core) for ARM virt machines which support sockets/clusters
> +    /cores/threads. Some members of the option can be omitted but their values
> +    will be automatically computed:
> +
> +    ::
> +
> +        -smp 16,sockets=2,clusters=2,cores=2,threads=2,maxcpus=16
> +
>      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
> -- 
> 2.27.0
>

Reviewed-by: Andrew Jones <drjones@redhat.com>