It turns out AMD gets x86_max_cores wrong when there are compute
units.
The issue is that Linux assumes:
nr_logical_cpus = nr_cores * nr_siblings
But AMD reports its CU unit as 2 cores, but then sets num_smp_siblings
to 2 as well.
Cc: Ingo Molnar <mi...@kernel.org>
Cc: Borislav Petkov <b...@alien8.de>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Andreas Herrmann <aherrm...@suse.com>
Reported-by: Xiong Zhou <jencce.ker...@gmail.com>
Fixes: 1f12e32f4cd5 ("x86/topology: Create logical package id")
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Link:
http://lkml.kernel.org/r/20160317095220.go6...@twins.programming.kicks-ass.net
---
arch/x86/kernel/cpu/amd.c | 8 ++++----
arch/x86/kernel/smpboot.c | 11 ++++++-----
2 files changed, 10 insertions(+), 9 deletions(-)
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -313,9 +313,9 @@ static void amd_get_topology(struct cpui
node_id = ecx & 7;
/* get compute unit information */
- smp_num_siblings = ((ebx >> 8) & 3) + 1;
+ cores_per_cu = smp_num_siblings = ((ebx >> 8) & 3) + 1;
+ c->x86_max_cores /= smp_num_siblings;
c->compute_unit_id = ebx & 0xff;
- cores_per_cu += ((ebx >> 8) & 3);
} else if (cpu_has(c, X86_FEATURE_NODEID_MSR)) {
u64 value;
@@ -331,8 +331,8 @@ static void amd_get_topology(struct cpui
u32 cus_per_node;
set_cpu_cap(c, X86_FEATURE_AMD_DCM);
- cores_per_node = c->x86_max_cores / nodes_per_socket;
- cus_per_node = cores_per_node / cores_per_cu;
+ cus_per_node = c->x86_max_cores / nodes_per_socket;
+ cores_per_node = cus_per_node * cores_per_cu;
/* store NodeID, use llc_shared_map to store sibling info */
per_cpu(cpu_llc_id, cpu) = node_id;
