On 3/15/21 1:16 PM, Cédric Le Goater wrote:
On 3/15/21 4:12 PM, Daniel Henrique Barboza wrote:
On 3/12/21 11:31 AM, Cédric Le Goater wrote:
Initial commit 15863ff3b8da ("powerpc: Make chip-id information
available to userspace") introduce a cpu_to_chip_id() routine for the
PowerNV platform using the "ibm,chip-id" property to query the chip id
of a CPU. But PAPR does not specify such a property and the node id
query is broken.
Use cpu_to_node() instead which guarantees to have a correct value on
all platforms, PowerNV an pSeries.
It is worth mentioning that that this patch will change how
topology_physical_package_id() represents in a QEMU guest. Right now,
ibm,chip-id
in QEMU is matching the socket-id. After this patch,
topology_physical_package_id()
will now match the NUMA id of the CPU.
yes. I should have added some more background.
LPARs are impacted by the use of ibm,chip-id because the property
does not exist under PowerVM and the topology-id in sysfs is always
-1 even if NUMA nodes are defined.
Under QEMU/KVM, ibm,chip-id is badly calculated when using uncommon
SMT configuration. This leads to a bogus topology-id value being
exported in sysfs.
The use of cpu_to_node() guarantees to have a correct NUMA node id
under both environments QEMU/KVM and PowerVM.
On the PowerNV platform, 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.
May be I should rephrase the commit log in a v2 ?
It's a fine idea, given that apparently we don't have documentation explaining
these details (well, at least I didn't find any). We can reference the commit
message later on as explanation :)
Thanks,
DHB
C.
Reviewed-by: Daniel Henrique Barboza <danielhb...@gmail.com>
Tested-by: Daniel Henrique Barboza <danielhb...@gmail.com>
Cc: Nathan Lynch <nath...@linux.ibm.com>
Cc: Srikar Dronamraju <sri...@linux.vnet.ibm.com>
Cc: Vasant Hegde <hegdevas...@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))
