[v8,07/21] i386/cpu: Use APIC ID info get NumSharingCache for CPUID[0x8000001D].EAX[bits 25:14]

Commit Message

Zhao Liu Jan. 31, 2024, 10:13 a.m. UTC

From: Zhao Liu <[e-mail]>

The commit 8f4202fb1080 ("i386: Populate AMD Processor Cache Information
for cpuid 0x8000001D") adds the cache topology for AMD CPU by encoding
the number of sharing threads directly.

From AMD's APM, NumSharingCache (CPUID[0x8000001D].EAX[bits 25:14])
means [1]:

The number of logical processors sharing this cache is the value of
this field incremented by 1. To determine which logical processors are
sharing a cache, determine a Share Id for each processor as follows:

ShareId = LocalApicId >> log2(NumSharingCache+1)

Logical processors with the same ShareId then share a cache. If
NumSharingCache+1 is not a power of two, round it up to the next power
of two.

From the description above, the calculation of this field should be same
as CPUID[4].EAX[bits 25:14] for Intel CPUs. So also use the offsets of
APIC ID to calculate this field.

[1]: APM, vol.3, appendix.E.4.15 Function 8000_001Dh--Cache Topology
     Information

Cc: Babu Moger <[e-mail]>
Tested-by: Yongwei Ma <[e-mail]>
Signed-off-by: Zhao Liu <[e-mail]>
---
Changes since v7:
 * Moved this patch after CPUID[4]'s similar change ("i386/cpu: Use APIC
   ID offset to encode cache topo in CPUID[4]"). (Xiaoyao)
 * Dropped Michael/Babu's Acked/Reviewed/Tested tags since the code
   change due to the rebase.
 * Re-added Yongwei's Tested tag For his re-testing (compilation on
   Intel platforms).

Changes since v3:
 * Rewrote the subject. (Babu)
 * Deleted the original "comment/help" expression, as this behavior is
   confirmed for AMD CPUs. (Babu)
 * Renamed "num_apic_ids" (v3) to "num_sharing_cache" to match spec
   definition. (Babu)

Changes since v1:
 * Renamed "l3_threads" to "num_apic_ids" in
   encode_cache_cpuid8000001d(). (Yanan)
 * Added the description of the original commit and add Cc.
---
 target/i386/cpu.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Patch

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 747cfb6cac03..65944645db5c 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -331,7 +331,7 @@  static void encode_cache_cpuid8000001d(CPUCacheInfo *cache,
                                        uint32_t *eax, uint32_t *ebx,
                                        uint32_t *ecx, uint32_t *edx)
 {
-    uint32_t l3_threads;
+    uint32_t num_sharing_cache;
     assert(cache->size == cache->line_size * cache->associativity *
                           cache->partitions * cache->sets);
 
@@ -340,11 +340,11 @@  static void encode_cache_cpuid8000001d(CPUCacheInfo *cache,
 
     /* L3 is shared among multiple cores */
     if (cache->level == 3) {
-        l3_threads = topo_info->cores_per_die * topo_info->threads_per_core;
-        *eax |= (l3_threads - 1) << 14;
+        num_sharing_cache = 1 << apicid_die_offset(topo_info);
     } else {
-        *eax |= ((topo_info->threads_per_core - 1) << 14);
+        num_sharing_cache = 1 << apicid_core_offset(topo_info);
     }
+    *eax |= (num_sharing_cache - 1) << 14;
 
     assert(cache->line_size > 0);
     assert(cache->partitions > 0);