Re: [Qemu-devel] [RFCv2 2/2] spapr: Fix default NUMA node allocation for threads

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 09/04/2015 02:51 PM, David Gibson wrote:
> At present, if guest numa nodes are requested, but the cpus in each node
> are not specified, spapr just uses the default behaviour or assigning each
> vcpu round-robin to nodes.
>
> If smp_threads != 1, that will assign adjacent threads in a core to
> different NUMA nodes.  As well as being just weird, that's a configuration
> that can't be represented in the device tree we give to the guest, which
> means the guest and qemu end up with different ideas of the NUMA topology.
>
> This patch implements mc->cpu_index_to_socket_id in the spapr code to
> make sure vcpus get assigned to nodes only at the socket granularity.
>
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>	


> ---
>   hw/ppc/spapr.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
>
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index dbc295b..8adef2d 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -2162,6 +2162,13 @@ static HotplugHandler *spapr_get_hotpug_handler(MachineState *machine,
>       return NULL;
>   }
>
> +static unsigned spapr_cpu_index_to_socket_id(unsigned cpu_index)
> +{
> +    /* Allocate to NUMA nodes on a "socket" basis (not that concept of
> +     * socket means much for the paravirtualized PAPR platform) */
> +    return cpu_index / smp_threads / smp_cores;
> +}
> +
>   static void spapr_machine_class_init(ObjectClass *oc, void *data)
>   {
>       MachineClass *mc = MACHINE_CLASS(oc);
> @@ -2183,6 +2190,7 @@ static void spapr_machine_class_init(ObjectClass *oc, void *data)
>       mc->get_hotplug_handler = spapr_get_hotpug_handler;
>       hc->plug = spapr_machine_device_plug;
>       hc->unplug = spapr_machine_device_unplug;
> +    mc->cpu_index_to_socket_id = spapr_cpu_index_to_socket_id;
>
>       smc->dr_lmb_enabled = false;
>       fwc->get_dev_path = spapr_get_fw_dev_path;
>


-- 
Alexey