diff --git a/llvm/lib/Support/Unix/Threading.inc b/llvm/lib/Support/Unix/Threading.inc
--- a/llvm/lib/Support/Unix/Threading.inc
+++ b/llvm/lib/Support/Unix/Threading.inc
@@ -371,6 +371,14 @@
   }
   return CPU_COUNT(&Enabled);
 }
+#elif defined(__linux__) && defined(__aarch64__)
+static int computeHostNumPhysicalCores() {
+  cpu_set_t Affinity;
+  if (sched_getaffinity(0, sizeof(Affinity), &Affinity) == 0)
+    return CPU_COUNT(&Affinity);
+ 
+  return -1;
+}
 #elif defined(__linux__) && defined(__s390x__)
 static int computeHostNumPhysicalCores() {
   return sysconf(_SC_NPROCESSORS_ONLN);
diff --git a/llvm/unittests/Support/Threading.cpp b/llvm/unittests/Support/Threading.cpp
--- a/llvm/unittests/Support/Threading.cpp
+++ b/llvm/unittests/Support/Threading.cpp
@@ -28,6 +28,7 @@
   // some systems.
   return (Host.isOSWindows() && llvm_is_multithreaded()) || Host.isOSDarwin() ||
          (Host.isX86() && Host.isOSLinux()) ||
+         (Host.isAArch64() && Host.isOSLinux()) ||
          (Host.isOSLinux() && !Host.isAndroid()) ||
          (Host.isSystemZ() && Host.isOSzOS());
 #else