Remove hyperthreading multiplier to improve performance.

Tests on my local machine show that the Hyperthreading multiplier is significantly hurting our builds times. Running with 8 logical cores is 11% faster than running with 4.8 cores when doing builds on my Mac.

macOS 10.12
MacBookPro 2017 (1 CPU, 4 core, 8 hyperthreaded)

1434.259 with --jobs = 5
1274.459 with --jobs = 8

I'll do some similar tests on Linux to see if it makes sense there.

PiperOrigin-RevId: 178654477

src/main/java/com/google/devtools/build/lib/actions/LocalHostResourceManagerDarwin.java

diff --git a/src/main/java/com/google/devtools/build/lib/actions/LocalHostResourceManagerDarwin.java b/src/main/java/com/google/devtools/build/lib/actions/LocalHostResourceManagerDarwin.java
index 3cde7f2..abaa7f9 100644
--- a/src/main/java/com/google/devtools/build/lib/actions/LocalHostResourceManagerDarwin.java
+++ b/src/main/java/com/google/devtools/build/lib/actions/LocalHostResourceManagerDarwin.java
@@ -24,16 +24,11 @@
 public class LocalHostResourceManagerDarwin {
   private static final Boolean JNI_UNAVAILABLE =
       "0".equals(System.getProperty("io.bazel.EnableJni"));
-  private static final double EFFECTIVE_CPUS_PER_HYPERTHREADED_CPU = 0.6;
 
   private static int getLogicalCpuCount() throws IOException {
     return (int) NativePosixSystem.sysctlbynameGetLong("hw.logicalcpu");
   }
 
-  private static int getPhysicalCpuCount() throws IOException {
-    return (int) NativePosixSystem.sysctlbynameGetLong("hw.physicalcpu");
-  }
-
   private static double getMemoryInMb() throws IOException {
     return NativePosixSystem.sysctlbynameGetLong("hw.memsize") / 1E6;
   }
@@ -44,13 +39,11 @@
     }
     try {
       int logicalCpuCount = getLogicalCpuCount();
-      int physicalCpuCount = getPhysicalCpuCount();
       double ramMb = getMemoryInMb();
-      boolean hyperthreading = (logicalCpuCount != physicalCpuCount);
 
       return ResourceSet.create(
           ramMb,
-          logicalCpuCount * (hyperthreading ? EFFECTIVE_CPUS_PER_HYPERTHREADED_CPU : 1.0),
+          logicalCpuCount,
           1.0,
           Integer.MAX_VALUE);
     } catch (IOException e) {