Massive performance loss from OS::sleep hack

[Kurt Miller]

David Xu confirmed for me that pthread_yield() does give some
time to lower priority threads on 7.0 using thr. Attached and inline
are two patches for the 1.5 port that is how I suggest the issue be
addressed.

For 7.0 and up default UseThreadPriorities to true and always
use pthread_yield(). For < 7.0 default UseThreadPriorities to
false and conditionally use pthread_yield()/os_sleep(). User's
can toggle UseThreadPriorities with the command line argument
-XX:+UseThreadPriorities

-------- files/patch-vm::os_bsd.cpp --------
$FreeBSD: ports/java/jdk15/files/patch-vm::os_bsd.cpp,v 1.7 2007/06/09 
05:14:56 glewis Exp $

--- ../../hotspot/src/os/bsd/vm/os_bsd.cpp.orig	Mon Sep 17 17:39:33 2007
+++ ../../hotspot/src/os/bsd/vm/os_bsd.cpp	Mon Sep 17 20:57:26 2007
@@ -508,7 +508,7 @@
 #define getenv(n) ::getenv(n)
 
 #ifndef DEFAULT_LD_LIBRARY_PATH
-#define DEFAULT_LD_LIBRARY_PATH "/usr/lib" /* See ld.so.1(1) */
+#define DEFAULT_LD_LIBRARY_PATH "/usr/lib:/usr/local/lib" /* See ld.so.1(1) 
*/
 #endif
 #define EXTENSIONS_DIR "/lib/ext"
 #define ENDORSED_DIR "/lib/endorsed"
@@ -2273,11 +2273,14 @@
 
 // BSDXXX: Only use pthread_yield here and below if the system thread
 // scheduler gives time slices to lower priority threads when yielding.
-#ifdef __FreeBSD__
+// pthread_yield() can also be used when thread priorities are disabled.
+// Using os_sleep() here causes significant performance degradation.
+#if defined(_ALLBSD_SOURCE) && (!defined(__FreeBSD__) || __FreeBSD__ < 7)
+  if ( UseThreadPriorities )
       os_sleep(MinSleepInterval, interruptible);
-#else
-      pthread_yield();
+  else
 #endif
+      pthread_yield();
 
 #if SOLARIS
       // XXX - This code was not exercised during the Merlin RC1
@@ -2299,11 +2302,14 @@
 
 // BSDXXX: Only use pthread_yield here and above if the system thread
 // scheduler gives time slices to lower priority threads when yielding.
-#ifdef __FreeBSD__
-    os_sleep(MinSleepInterval, interruptible);
-#else
-    pthread_yield();
+// pthread_yield() can be also used when thread priorities are disabled.
+// Using os_sleep() here causes significant performance degradation.
+#if defined(_ALLBSD_SOURCE) && (!defined(__FreeBSD__) || __FreeBSD__ < 7)
+  if ( UseThreadPriorities )
+      os_sleep(MinSleepInterval, interruptible);
+  else
 #endif
+      pthread_yield();
     return 0;
   }
 
------- files/patch-vm::globals.hpp --------
$FreeBSD$

--- ../../hotspot/src/share/vm/runtime/globals.hpp.orig	Mon Sep 17 10:12:16 
2007
+++ ../../hotspot/src/share/vm/runtime/globals.hpp	Mon Sep 17 10:20:32 2007
@@ -130,6 +130,12 @@
 #define falseInProduct true
 #endif
 
+#if !defined(_ALLBSD_SOURCE) || (defined(__FreeBSD__) && __FreeBSD__ >= 7)
+#define OSUseThreadPriorities true
+#else
+#define OSUseThreadPriorities false
+#endif
+
 // develop flags are settable / visible only during development and are 
constant in the PRODUCT version
 // product flags are always settable / visible
 
@@ -2546,7 +2552,7 @@
           "beginning to throw OutOfMemoryErrors in each compile")           \
                                                                             \
   /* Priorities */                                                          \
-  product(bool, UseThreadPriorities, true,                                  \
+  product(bool, UseThreadPriorities, OSUseThreadPriorities,                 \
           "Use native thread priorities")	                            \
                                                                             \
   product(intx, ThreadPriorityPolicy, 0,                                    \