8278020: ~13% variation in Renaissance-Scrabble

Reviewed-by: dholmes, stuefe, kvn

Author: iklam

src/hotspot/share/oops/klass.hpp

@@ -117,8 +117,8 @@ class Klass : public Metadata {
   // Klass identifier used to implement devirtualized oop closure dispatching.
   const KlassID _id;
 
-  // vtable length
-  int _vtable_len;
+  // Processed access flags, for use by Class.getModifiers.
+  jint        _modifier_flags;
 
   // The fields _super_check_offset, _secondary_super_cache, _secondary_supers
   // and _primary_supers all help make fast subtype checks.  See big discussion
@@ -154,7 +154,10 @@ class Klass : public Metadata {
   // Provide access the corresponding instance java.lang.ClassLoader.
   ClassLoaderData* _class_loader_data;
 
-  jint        _modifier_flags;  // Processed access flags, for use by Class.getModifiers.
+  int _vtable_len;              // vtable length. This field may be read very often when we
+                                // have lots of itable dispatches (e.g., lambdas and streams).
+                                // Keep it away from the beginning of a Klass to avoid cacheline
+                                // contention that may happen when a nearby object is modified.
   AccessFlags _access_flags;    // Access flags. The class/interface distinction is stored here.
 
   JFR_ONLY(DEFINE_TRACE_ID_FIELD;)