Re: [PATCH v2 3/3] spapr_numa.c: fix ibm,max-associativity-domains calculation

[Greg Kurz <groug@kaod.org>]

On Thu, 28 Jan 2021 14:42:13 -0300
Daniel Henrique Barboza <danielhb413@gmail.com> 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
>                  00000004 00000008 00000008 00000008 00000008
> 
> This overtuning of maxdomains doesn't go unnoticed in the guest, being
> detected in SLUB during boot:
> 
>  dmesg | grep SLUB
> [    0.000000] 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 just
> spapr->gpu_numa_id.
> 
> Reported-by: Cédric Le Goater <clg@kaod.org>
> Tested-by: Cédric Le Goater <clg@kaod.org>
> Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
> ---

Reviewed-by: Greg Kurz <groug@kaod.org>

>  hw/ppc/spapr_numa.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/ppc/spapr_numa.c b/hw/ppc/spapr_numa.c
> index a757dd88b8..779f18b994 100644
> --- a/hw/ppc/spapr_numa.c
> +++ b/hw/ppc/spapr_numa.c
> @@ -311,6 +311,8 @@ 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->gpu_numa_id -
> +                                   spapr_numa_initial_nvgpu_numa_id(ms);
>      uint32_t refpoints[] = {
>          cpu_to_be32(0x4),
>          cpu_to_be32(0x3),
> @@ -318,7 +320,7 @@ 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),