* More or less reverted my previous thread_yield() change: while this gives

threads with higher priorities a much better scheduling experience, it
  also creates a problem as soon as more than one higher priority thread
  waits on a resource held by a lower priority thread; the higher priority
  threads play ping-pong, and the lower priority thread doesn't get it's
  chance.
* Increased the probability of skipping a thread priority.
* I won't do any other changes on the scheduler, that's meianote's job now :-)


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@20758 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/system/kernel/scheduler.cpp

@@ -189,12 +189,14 @@ scheduler_reschedule(void)
 	} else {
 		// select next thread from the run queue
 		while (nextThread && nextThread->priority > B_IDLE_PRIORITY) {
+#if 0
 			if (oldThread == nextThread && nextThread->was_yielded) {
 				// ignore threads that called thread_yield() once
 				nextThread->was_yielded = false;
 				prevThread = nextThread;
 				nextThread = nextThread->queue_next;
 			}
+#endif
 
 			// always extract real time threads
 			if (nextThread->priority >= B_FIRST_REAL_TIME_PRIORITY)
@@ -205,7 +207,7 @@ scheduler_reschedule(void)
 				break;
 
 			// skip normal threads sometimes (roughly 16%)
-			if (_rand() > 0x1500)
+			if (_rand() > 0x2000)
 				break;
 
 			// skip until next lower priority

src/system/kernel/thread.c

@@ -1307,7 +1307,8 @@ thread_yield(void)
 	GRAB_THREAD_LOCK();
 
 	// mark the thread as yielded, so it will not be scheduled next
-	thread->was_yielded = true;
+	//thread->was_yielded = true;
+	thread->next_priority = B_LOWEST_ACTIVE_PRIORITY;
 	scheduler_reschedule();
 
 	RELEASE_THREAD_LOCK();