cpuid/x86: use leaf 80000008 for AMD physical core counts

cpuid/x86.cpp

@@ -42,17 +42,48 @@ cpuid_t cpuid (u32 query, u32 param = 0)
 }
 
 
+///////////////////////////////////////////////////////////////////////////////
+namespace {
+    enum vendor_t {
+        INTEL,
+        AMD,
+
+        UNKNOWN
+    };
+}
+
+
+//-----------------------------------------------------------------------------
+static constexpr
+vendor_t
+find_vendor (cpuid_t const &leaf0)
+{
+    constexpr struct {
+        u32 b, c, d;
+        vendor_t vendor;
+    } VALUES[] = {
+        { 0x68747541, 0x444d4163, 0x69746e65, AMD },
+        { 0x756e6547, 0x6c65746e, 0x49656e69, INTEL },
+    };
+
+    for (auto const &v: VALUES) {
+        if (v.b == leaf0.b && v.c == leaf0.c && v.d == leaf0.d)
+            return v.vendor;
+    }
+
+    return UNKNOWN;
+}
+
+
 ///////////////////////////////////////////////////////////////////////////////
 x86::x86 ()
 {
-    const auto &[largest_function, vendor0, vendor2, vendor1] = cpuid (0);
+    auto const leaf0 = cpuid (0);
-    (void)largest_function;
+    memcpy (vendor_name.data () + 0, &leaf0.b, sizeof (leaf0.b));
+    memcpy (vendor_name.data () + 4, &leaf0.d, sizeof (leaf0.d));
+    memcpy (vendor_name.data () + 8, &leaf0.c, sizeof (leaf0.c));
 
-    memcpy (vendor_name.data () + 0, &vendor0, sizeof (vendor0));
+    auto const vendor = find_vendor (leaf0);
-    memcpy (vendor_name.data () + 4, &vendor1, sizeof (vendor1));
-    memcpy (vendor_name.data () + 8, &vendor2, sizeof (vendor2));
-
-    const bool is_amd = vendor0 == 0x68747541 && vendor1 == 0x69746e65 && vendor2 == 0x444d4163;
 
     {
         auto features = cpuid (1);
@@ -66,7 +97,10 @@ x86::x86 ()
         simd.sse2  = features.d & (1u << 26);
 
         cores.hyper_threading = features.d & (1u << 28);
+        if (cores.hyper_threading)
             cores.logical = from_bits (features.b, 23, 16);
+        else
+            cores.logical = 0;
     }
 
     {
@@ -79,16 +113,36 @@ x86::x86 ()
         memcpy (&product_name[0x20], &product2, sizeof (product2));
     }
 
-    // Function 4 isn't implemented by AMD. Intel uses it for cache
+    if (vendor == INTEL) {
-    // descriptors. It has some useful information (like procesor counts) but
+        cores.logical = cores.physical = 0;
-    // it's ugly as sin; try to avoid using it.
-    // { (void)cpuid (0x0b, 4); }
 
-    if (is_amd) {
+        for (int level = 0; true; ++level) {
-        auto long_mode = cpuid (0x8000'0008);
+            auto const param = cpuid (0x4, level);
-        auto apic_id_size = from_bits (long_mode.c, 15, 12);
+
-        (void)apic_id_size;
+            // The final level will set the 'cache type' bits to zero to
-        cores.physical = 0; //from_bits (long_mode.c, 7, 0) + 1;
+            // indicate there are no more caches.
+            if ((param.a & 0b1111) == 0)
+                break;
+
+            cores.physical = max (
+                cores.physical,
+                cruft::cast::lossless<int> (from_bits (param.a, 31, 26)) + 1
+            );
+            cores.logical = max (
+                cores.physical,
+                cruft::cast::lossless<int> (from_bits (param.a, 25, 14)) + 1
+            );
+        }
+    } else if (vendor == AMD) {
+        auto const size_identifiers = cpuid (0x8000'0008);
+
+        if (auto const apic_id_size = from_bits (size_identifiers.c, 15, 12); apic_id_size) {
+            cores.physical = 1 << (apic_id_size - 1);
+        } else {
+            cores.physical = (size_identifiers.c & 0xff) + 1;
+        }
+    } else {
+        cores.physical = 0;
     }
 }