Re: [PATCH] hw/arm/virt: Expose empty NUMA nodes through ACPI

[Igor Mammedov]

On Tue, 26 Oct 2021 07:41:01 +0800
Gavin Shan <gshan@redhat.com> wrote:

> The empty NUMA nodes, where no memory resides, aren't exposed
> through ACPI SRAT table. It's not user preferred behaviour because
> the corresponding memory node devices are missed from the guest
> kernel as the following example shows, and memory can't be hot
> added to these empty NUMA nodes at later point.

a error message one gets would be useful here.

btw:
memory hotplug seems to work for x86 without adding empty nodes.
So it beg a question, if absence of empty nodes is the issue here.

> 
>   /home/gavin/sandbox/qemu.main/build/qemu-system-aarch64 \
>   -accel kvm -machine virt,gic-version=host               \
>   -cpu host -smp 4,sockets=2,cores=2,threads=1            \
>   -m 1024M,slots=16,maxmem=64G                            \
>   -object memory-backend-ram,id=mem0,size=512M            \
>   -object memory-backend-ram,id=mem1,size=512M            \
>   -numa node,nodeid=0,cpus=0-1,memdev=mem0                \
>   -numa node,nodeid=1,cpus=2-3,memdev=mem1                \
>   -numa node,nodeid=2                                     \
>   -numa node,nodeid=3                                     \
>      :
>   guest# ls /sys/devices/system/node | grep node
>   node0
>   node1
>   node2
> 
> This exposes these empty NUMA nodes through ACPI SRAT table. With
> this applied, the corresponding memory node devices can be found
> from the guest. Note that the hotpluggable capability is explicitly
> given to these empty NUMA nodes for sake of completeness.
> 
>   guest# ls /sys/devices/system/node | grep node
>   node0
>   node1
>   node2
>   node3
> 
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
>  hw/arm/virt-acpi-build.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
> index 674f902652..a4c95b2f64 100644
> --- a/hw/arm/virt-acpi-build.c
> +++ b/hw/arm/virt-acpi-build.c
> @@ -526,6 +526,7 @@ build_srat(GArray *table_data, BIOSLinker *linker, 
> VirtMachineState *vms)
>      const CPUArchIdList *cpu_list = mc->possible_cpu_arch_ids(ms);
>      AcpiTable table = { .sig = "SRAT", .rev = 3, .oem_id = vms->oem_id,
>                          .oem_table_id = vms->oem_table_id };
> +    MemoryAffinityFlags flags;
>  
>      acpi_table_begin(&table, table_data);
>      build_append_int_noprefix(table_data, 1, 4); /* Reserved */
> @@ -547,12 +548,15 @@ build_srat(GArray *table_data, BIOSLinker *linker, 
> VirtMachineState *vms)
>  
>      mem_base = vms->memmap[VIRT_MEM].base;
>      for (i = 0; i < ms->numa_state->num_nodes; ++i) {
> -        if (ms->numa_state->nodes[i].node_mem > 0) {
> -            build_srat_memory(table_data, mem_base,
> -                              ms->numa_state->nodes[i].node_mem, i,
> -                              MEM_AFFINITY_ENABLED);
> -            mem_base += ms->numa_state->nodes[i].node_mem;
> +        if (ms->numa_state->nodes[i].node_mem) {
> +            flags = MEM_AFFINITY_ENABLED;
> +        } else {
> +            flags = MEM_AFFINITY_ENABLED | MEM_AFFINITY_HOTPLUGGABLE;
>          }
> +
> +        build_srat_memory(table_data, mem_base,
> +                          ms->numa_state->nodes[i].node_mem, i, flags);
> +        mem_base += ms->numa_state->nodes[i].node_mem;
>      }
>  
>      if (ms->nvdimms_state->is_enabled) {