Detect the number of performance cores in the M1 macs via the new mac…

…os12 API (JuliaLang#44072)

* Use the new macos12 api to query perf cores

src/sys.c

@@ -618,14 +618,23 @@ JL_DLLEXPORT int jl_cpu_threads(void) JL_NOTSAFEPOINT
     }
 
 #if defined(__APPLE__) && defined(_CPU_AARCH64_)
-    // Manually subtract efficiency cores for Apple's big.LITTLE cores
-    int32_t family = 0;
-    len = 4;
-    sysctlbyname("hw.cpufamily", &family, &len, NULL, 0);
-    if (family >= 1 && count > 1) {
-        if (family == CPUFAMILY_ARM_FIRESTORM_ICESTORM) {
-            // We know the Apple M1 has 4 efficiency cores, so subtract them out.
-            count -= 4;
+//MacOS 12 added a way to query performance cores
+    char buf[7];
+    len = 7;
+    sysctlbyname("kern.osrelease", buf, &len, NULL, 0);
+    if (buf[0] > 1 && buf[1] > 0){
+        len = 4;
+        sysctlbyname("hw.perflevel0.physicalcpu", &count, &len, NULL, 0);
+    }
+    else {
+        int32_t family = 0;
+        len = 4;
+        sysctlbyname("hw.cpufamily", &family, &len, NULL, 0);
+        if (family >= 1 && count > 1) {
+            if (family == CPUFAMILY_ARM_FIRESTORM_ICESTORM) {
+                // We know the Apple M1 has 4 efficiency cores, so subtract them out.
+                count -= 4;
+            }
         }
     }
 #endif