On Thu, 28 Jan 2021 12:17:31 -0300
Daniel Henrique Barboza wrote:
> The current logic for calculating 'maxdomain' making it a sum of
> numa_state->num_nodes with spapr->gpu_numa_id. spapr->gpu_numa_id is
> used as a index to determine the next available NUMA id that a
> given NVGPU can use.
>
> The problem is that the initial value of gpu_numa_id, for any topology
> that has more than one NUMA node, is equal to numa_state->num_nodes.
> This means that our maxdomain will always be, at least, twice the
> amount of existing NUMA nodes. This means that a guest with 4 NUMA
> nodes will end up with the following max-associativity-domains:
>
> rtas/ibm,max-associativity-domains
> 0004 0008 0008 0008 0008
>
> This overtuning of maxdomains doesn't go unnoticed in the guest, being
> detected in SLUB during boot:
>
> dmesg | grep SLUB
> [0.00] SLUB: HWalign=128, Order=0-3, MinObjects=0, CPUs=4, Nodes=8
>
> SLUB is detecting 8 total nodes, with 4 nodes being online.
>
> This patch fixes ibm,max-associativity-domains by considering the amount
> of NVGPUs NUMA nodes presented in the guest, instead of
> spapr->gpu_numa_id.
>
> Reported-by: Cédric Le Goater
> Signed-off-by: Daniel Henrique Barboza
> ---
> hw/ppc/spapr_numa.c | 16 +++-
> 1 file changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/hw/ppc/spapr_numa.c b/hw/ppc/spapr_numa.c
> index f71105c783..f4d6abce87 100644
> --- a/hw/ppc/spapr_numa.c
> +++ b/hw/ppc/spapr_numa.c
> @@ -60,6 +60,19 @@ unsigned int spapr_numa_initial_nvgpu_NUMA_id(MachineState
> *machine)
> return MAX(1, machine->numa_state->num_nodes);
> }
>
> +/*
> + * Note: if called before spapr_phb_pci_collect_nvgpu() finishes collecting
> + * all NVGPUs, this function will not give the right number of NVGPUs NUMA
> + * nodes.
> + */
This helper has exactly one user : spapr_numa_write_rtas_dt(). Maybe just
open-code it there, with a comment that spapr->gpu_numa_id is assumed to
be correct at the time we populate the device tree ?
> +static
> +unsigned int spapr_numa_get_number_nvgpus_nodes(SpaprMachineState *spapr)
> +{
> +MachineState *ms = MACHINE(spapr);
> +
> +return spapr->gpu_numa_id - spapr_numa_initial_nvgpu_NUMA_id(ms);
> +}
> +
> /*
> * This function will translate the user distances into
> * what the kernel understand as possible values: 10
> @@ -311,6 +324,7 @@ void spapr_numa_write_rtas_dt(SpaprMachineState *spapr,
> void *fdt, int rtas)
> {
> MachineState *ms = MACHINE(spapr);
> SpaprMachineClass *smc = SPAPR_MACHINE_GET_CLASS(spapr);
> +uint32_t number_nvgpus_nodes = spapr_numa_get_number_nvgpus_nodes(spapr);
> uint32_t refpoints[] = {
> cpu_to_be32(0x4),
> cpu_to_be32(0x3),
> @@ -318,7 +332,7 @@ void spapr_numa_write_rtas_dt(SpaprMachineState *spapr,
> void *fdt, int rtas)
> cpu_to_be32(0x1),
> };
> uint32_t nr_refpoints = ARRAY_SIZE(refpoints);
> -uint32_t maxdomain = ms->numa_state->num_nodes + spapr->gpu_numa_id;
> +uint32_t maxdomain = ms->numa_state->num_nodes + number_nvgpus_nodes;
> uint32_t maxdomains[] = {
> cpu_to_be32(4),
> cpu_to_be32(maxdomain),
