Update thread_create to only yield CPU to the new thread if necessary

src/threads/thread.c

@@ -261,7 +261,11 @@ thread_create (const char *name, int priority,
 
   /* Add to run queue. */
   thread_unblock (t);
-  thread_yield ();
+
+  /* Yield if the newly created thread has higher priority than the current
+     thread. */
+  if (t->priority > thread_current ()->priority)
+    thread_yield ();
 
   return tid;
 }