Current fixup causes cpu_core_id for family17 w/ downcore configuration
to be incorrect as shown here:
NODE: 0
processor 0 core id : 0
processor 1 core id : 1
processor 2 core id : 2
processor 3 core id : 4
processor 4 core id : 5
processor 5 core id : 0
NODE: 1
processor 6 core id : 2
processor 7 core id : 3
processor 8 core id : 4
processor 9 core id : 0
processor 10 core id : 1
processor 11 core id : 2
This could cause issue for code that relies on the cpu_core_id to be unique
(at least within the node).
Although the fixup is not needed, it has been around prior to family17h.
So, only apply the fixup for pre-family17h. The new value for cpu_core_id
for family17h and later will represent the CPUID_Fn8000001E_EBX[CoreId],
which is guaranteed to be unique for each core within a socket. Here are
example of the new cpu_core_id numbering scheme.
NODE: 0
processor 0 core id : 0
processor 1 core id : 1
processor 2 core id : 2
processor 3 core id : 4
processor 4 core id : 5
processor 5 core id : 6
NODE: 1
processor 6 core id : 8
processor 7 core id : 9
processor 8 core id : 10
processor 9 core id : 12
processor 10 core id : 13
processor 11 core id : 14
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpa...@amd.com>
---
Note: This patch is reworked based on prior discussion of another
patch series (https://lkml.org/lkml/2017/7/24/139), which is
now taking a new approach.
arch/x86/kernel/cpu/amd.c | 29 +++++++++++++++++++++++------
1 file changed, 23 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index bb5abe8..223dd8c 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -297,6 +297,28 @@ static int nearby_node(int apicid)
#endif
/*
+ * Only fixup cpu_core_id for pre-family17h systems to be in the
+ * [0 .. cores_per_node - 1] range. This is not really needed,
+ * but mainly kept so that we do not break any existing code,
+ * which may make this assumption on older platforms.
+ *
+ * For family17h and later, this logic is not applicable as cpu_core_id
+ * is the CoreId from CPUID_Fn8000001E_EBX, which is non-contiguous for
+ * downcore system configuration. This could break the logic and result
+ * in invalid cpu_core_id.
+ */
+static void __fixup_multi_node(struct cpuinfo_x86 *c)
+{
+ u32 cus_per_node;
+
+ if (c->x86 >= 0x17)
+ return;
+
+ cus_per_node = c->x86_max_cores / nodes_per_socket;
+ c->cpu_core_id %= cus_per_node;
+}
+
+/*
* Fixup core topology information for
* (1) AMD multi-node processors
* Assumption: Number of cores in each internal node is the same.
@@ -353,15 +375,10 @@ static void amd_get_topology(struct cpuinfo_x86 *c)
} else
return;
- /* fixup multi-node processor information */
if (nodes_per_socket > 1) {
- u32 cus_per_node;
-
set_cpu_cap(c, X86_FEATURE_AMD_DCM);
- cus_per_node = c->x86_max_cores / nodes_per_socket;
- /* core id has to be in the [0 .. cores_per_node - 1] range */
- c->cpu_core_id %= cus_per_node;
+ __fixup_multi_node(c);
}
}
#endif
--
2.7.4
