On Tue, Mar 16, 2021 at 01:24:37PM +0100, Cédric Le Goater wrote: > The topology-id of a CPU in a pSeries machine can be queried from > sysfs but under PowerVM the value is always -1 even if NUMA nodes are > defined. This is because the topology_physical_package_id() routine is > using the "ibm,chip-id" property which is not specified in PAPR. > > Under QEMU/KVM, things are different because QEMU populates the CPU DT > node with "ibm,chip-id" property. However, its value can be incorrect > for uncommon SMT configuration and expose a bogus topology-id value in > sysfs.
Incorrect in what sense? It's still indicating the (admittedly
arbitrary) qemu socket number, isn't it? And isn't that what it
should be?
> The use of cpu_to_node() guarantees to have a correct NUMA node id
> under both environments QEMU/KVM and PowerVM. This introduces a slight
> change for the QEMU/KVM guest, as the topology-id now matches the NUMA
> node and not the socket-id as before. Since QEMU also needs to remove
> "ibm,chip-id" property for the DT to follow the PAPR specs, both
> hypervisor environments will be in sync.
>
> On the PowerNV side, the NUMA node id returned by cpu_to_node() is
> computed from the "ibm,associativity" property of the CPU. Its value
> is built from the OPAL chip id and is equivalent to "ibm,chip-id".
Like mpe, I'm not convinced this is the right approach. "physical
packate" and NUMA node are not the same thing, except sometimes by
accident.
>
> Cc: Nathan Lynch <nath...@linux.ibm.com>
> Cc: Srikar Dronamraju <sri...@linux.vnet.ibm.com>
> Cc: Vasant Hegde <hegdevas...@linux.vnet.ibm.com>
> Reviewed-by: Greg Kurz <gr...@kaod.org>
> Reviewed-by: Daniel Henrique Barboza <danielhb...@gmail.com>
> Tested-by: Daniel Henrique Barboza <danielhb...@gmail.com>
> Reviewed-by: Srikar Dronamraju <sri...@linux.vnet.ibm.com>
> Signed-off-by: Cédric Le Goater <c...@kaod.org>
> ---
> arch/powerpc/include/asm/topology.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/include/asm/topology.h
> b/arch/powerpc/include/asm/topology.h
> index 3beeb030cd78..887c42a4e43d 100644
> --- a/arch/powerpc/include/asm/topology.h
> +++ b/arch/powerpc/include/asm/topology.h
> @@ -123,7 +123,7 @@ static inline int cpu_to_coregroup_id(int cpu)
> #ifdef CONFIG_PPC64
> #include <asm/smp.h>
>
> -#define topology_physical_package_id(cpu) (cpu_to_chip_id(cpu))
> +#define topology_physical_package_id(cpu) (cpu_to_node(cpu))
>
> #define topology_sibling_cpumask(cpu) (per_cpu(cpu_sibling_map, cpu))
> #define topology_core_cpumask(cpu) (cpu_cpu_mask(cpu))
--
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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