--- xnu/xnu-517.7.21/iokit/Kernel/IOUserClient.cpp
+++ xnu/xnu-517.9.4/iokit/Kernel/IOUserClient.cpp
@@ -383,7 +383,7 @@
         OSNotificationHeader		notifyHeader;
     };
 
-    enum { kMaxOutstanding = 256 };
+    enum { kMaxOutstanding = 1024 };
 
     PingMsg *		pingMsg;
     vm_size_t		msgSize;