On Mon, Nov 19, 2018 at 11:23:05AM -0500, Serhii Popovych wrote:
> Laurent Vivier reported off by one with maximum number of NUMA nodes
> provided by qemu-kvm being less by one than required according to
> description of "ibm,max-associativity-domains" property in LoPAPR.
>
> It appears that I incorrectly treated LoPAPR description of this
> property assuming it provides last valid domain (NUMA node here)
> instead of maximum number of domains.
>
> ### Before hot-add
>
> (qemu) info numa
> 3 nodes
> node 0 cpus: 0
> node 0 size: 0 MB
> node 0 plugged: 0 MB
> node 1 cpus:
> node 1 size: 1024 MB
> node 1 plugged: 0 MB
> node 2 cpus:
> node 2 size: 0 MB
> node 2 plugged: 0 MB
>
> $ numactl -H
> available: 2 nodes (0-1)
> node 0 cpus: 0
> node 0 size: 0 MB
> node 0 free: 0 MB
> node 1 cpus:
> node 1 size: 999 MB
> node 1 free: 658 MB
> node distances:
> node 0 1
> 0: 10 40
> 1: 40 10
>
> ### Hot-add
>
> (qemu) object_add memory-backend-ram,id=mem0,size=1G
> (qemu) device_add pc-dimm,id=dimm1,memdev=mem0,node=2
> (qemu) [ 87.704898] pseries-hotplug-mem: Attempting to hot-add 4 ...
> <there is no "Initmem setup node 2 [mem 0xHEX-0xHEX]">
> [ 87.705128] lpar: Attempting to resize HPT to shift 21
> ... <HPT resize messages>
>
> ### After hot-add
>
> (qemu) info numa
> 3 nodes
> node 0 cpus: 0
> node 0 size: 0 MB
> node 0 plugged: 0 MB
> node 1 cpus:
> node 1 size: 1024 MB
> node 1 plugged: 0 MB
> node 2 cpus:
> node 2 size: 1024 MB
> node 2 plugged: 1024 MB
>
> $ numactl -H
> available: 2 nodes (0-1)
> ^^^^^^^^^^^^^^^^^^^^^^^^
> Still only two nodes (and memory hot-added to node 0 below)
> node 0 cpus: 0
> node 0 size: 1024 MB
> node 0 free: 1021 MB
> node 1 cpus:
> node 1 size: 999 MB
> node 1 free: 658 MB
> node distances:
> node 0 1
> 0: 10 40
> 1: 40 10
>
> After fix applied numactl(8) reports 3 nodes available and memory
> plugged into node 2 as expected.
>
> Fixes: da9f80fbad21 ("spapr: Add ibm,max-associativity-domains property")
> Reported-by: Laurent Vivier <lviv...@redhat.com>
> Signed-off-by: Serhii Popovych <spopo...@redhat.com>
> ---
> v2
> Remove now unneeded ?: statement previously used to catch -1 as numa node
> causing Linux guests hanging on boot.
>
> hw/ppc/spapr.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 7afd1a1..a7171fb 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -1033,7 +1033,7 @@ static void spapr_dt_rtas(sPAPRMachineState *spapr,
> void *fdt)
> cpu_to_be32(0),
> cpu_to_be32(0),
> cpu_to_be32(0),
> - cpu_to_be32(nb_numa_nodes ? nb_numa_nodes - 1 : 0),
> + cpu_to_be32(nb_numa_nodes),
Sorry, I know this got discussed in the thread on the earlier version,
but I'd prefer we leave the conditional expression in here.
qemu makes a distinction between "non NUMA" (nb_numa_nodes == 0) and
"NUMA with one node" (nb_numa_nodes == 1). But from a PAPR guests's
point of view these are equivalent. I don't want to present two
different cases to the guest when we don't need to, so even though the
guest can handle it, I'd prefer we put a '1' here for both the
nb_numa_nodes == 0 and nb_numa_nodes == 1 case.
> };
>
> _FDT(rtas = fdt_add_subnode(fdt, 0, "rtas"));
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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