Index: linux-2.6.11-rc1-mm2/kernel/sched.c
===================================================================
--- linux-2.6.11-rc1-mm2.orig/kernel/sched.c	2005-01-22 09:36:27.000000000 +1100
+++ linux-2.6.11-rc1-mm2/kernel/sched.c	2005-01-22 09:36:49.000000000 +1100
@@ -2499,7 +2499,13 @@ void scheduler_tick(void)
 	task_t *p = current;
 
 	rq->timestamp_last_tick = sched_clock();
-	if (iso_task(p) && !rq->iso_refractory)
+	/*
+	 * The iso_ticks accounting is incremented only when a SCHED_ISO task
+	 * is running in soft rt mode. Running rt_tasks are also accounted
+	 * to make the iso_cpu a proportion of cpu available for SCHED_NORMAL
+	 * tasks only.
+	 */
+	if (rt_task(p) || (iso_task(p) && !rq->iso_refractory))
 		inc_iso_ticks(rq, p);
 	else
 		dec_iso_ticks(rq, p);