Re: [Qemu-devel] [PATCH] numa: Introduce MachineClass::auto_enable_numa for implicit NUMA node

[Igor Mammedov <imammedo@redhat.com>]

On Mon,  5 Aug 2019 15:13:02 +0800
Tao Xu <tao3.xu@intel.com> wrote:

> Add MachineClass::auto_enable_numa field. When it is true, a NUMA node
> is expected to be created implicitly.
> 
> Acked-by: David Gibson <david@gibson.dropbear.id.au>
> Suggested-by: Igor Mammedov <imammedo@redhat.com>
> Suggested-by: Eduardo Habkost <ehabkost@redhat.com>
> Signed-off-by: Tao Xu <tao3.xu@intel.com>
> ---
> 
> This patch has a dependency on
> https://patchwork.kernel.org/cover/11063235/
> ---
>  hw/core/numa.c      | 9 +++++++--
>  hw/ppc/spapr.c      | 9 +--------
>  include/hw/boards.h | 1 +
>  3 files changed, 9 insertions(+), 10 deletions(-)
> 
> diff --git a/hw/core/numa.c b/hw/core/numa.c
> index 75db35ac19..756d243d3f 100644
> --- a/hw/core/numa.c
> +++ b/hw/core/numa.c
> @@ -580,9 +580,14 @@ void numa_complete_configuration(MachineState *ms)
>       *   guest tries to use it with that drivers.
>       *
>       * Enable NUMA implicitly by adding a new NUMA node automatically.
> +     *
> +     * Or if MachineClass::auto_enable_numa is true and no NUMA nodes,
> +     * assume there is just one node with whole RAM.
>       */
> -    if (ms->ram_slots > 0 && ms->numa_state->num_nodes == 0 &&
> -        mc->auto_enable_numa_with_memhp) {
> +    if (ms->numa_state->num_nodes == 0 &&
> +        ((ms->ram_slots > 0 &&
> +        mc->auto_enable_numa_with_memhp) ||
> +        mc->auto_enable_numa)) {
>              NumaNodeOptions node = { };
>              parse_numa_node(ms, &node, &error_abort);
>      }
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index f607ca567b..e50343f326 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -400,14 +400,6 @@ static int spapr_populate_memory(SpaprMachineState *spapr, void *fdt)
>      hwaddr mem_start, node_size;
>      int i, nb_nodes = machine->numa_state->num_nodes;
>      NodeInfo *nodes = machine->numa_state->nodes;
> -    NodeInfo ramnode;
> -
> -    /* No NUMA nodes, assume there is just one node with whole RAM */
> -    if (!nb_nodes) {
> -        nb_nodes = 1;
> -        ramnode.node_mem = machine->ram_size;
> -        nodes = &ramnode;
> -    }
>  
>      for (i = 0, mem_start = 0; i < nb_nodes; ++i) {
>          if (!nodes[i].node_mem) {
> @@ -4369,6 +4361,7 @@ static void spapr_machine_class_init(ObjectClass *oc, void *data)
>       */
>      mc->numa_mem_align_shift = 28;
>      mc->numa_mem_supported = true;
> +    mc->auto_enable_numa = true;

this will always create a numa node (that will affect not only RAM but
also all other components that depends on numa state (like CPUs)),
where as spapr_populate_memory() was only faking numa node in DT for RAM.
It makes non-numa configuration impossible.
Seeing David's ACK on the patch it might be fine, but I believe
commit message should capture that and explain why the change in
behavior is fine.

>      smc->default_caps.caps[SPAPR_CAP_HTM] = SPAPR_CAP_OFF;
>      smc->default_caps.caps[SPAPR_CAP_VSX] = SPAPR_CAP_ON;
> diff --git a/include/hw/boards.h b/include/hw/boards.h
> index 2eb9a0b4e0..4a350b87d2 100644
> --- a/include/hw/boards.h
> +++ b/include/hw/boards.h
> @@ -220,6 +220,7 @@ struct MachineClass {
>      bool smbus_no_migration_support;
>      bool nvdimm_supported;
>      bool numa_mem_supported;
> +    bool auto_enable_numa;
>  
>      HotplugHandler *(*get_hotplug_handler)(MachineState *machine,
>                                             DeviceState *dev);