place work-stealing queue indices on different cache lines to avoid false-sharing

Author: d-netto

src/work-stealing-queue.h

@@ -36,6 +36,13 @@ static inline ws_array_t *create_ws_array(size_t capacity, int32_t eltsz) JL_NOT
 
 typedef struct {
     _Atomic(int64_t) top;
+    // put `top` and `bottom` on different cache lines
+    // to avoid false sharing
+#ifdef _P64
+    void *_ignore[7];
+#else
+    void *_ignore[15];
+#endif
     _Atomic(int64_t) bottom;
     _Atomic(ws_array_t *) array;
 } ws_queue_t;