diff -r bb9a7d40d0b5 xen/common/sched_credit.c
--- a/xen/common/sched_credit.c	Mon Sep 01 13:01:23 2008 +0100
+++ b/xen/common/sched_credit.c	Mon Sep 01 13:01:37 2008 +0100
@@ -61,7 +61,9 @@
 /*
  * Flags
  */
-#define CSCHED_FLAG_VCPU_PARKED 0x0001  /* VCPU over capped credits */
+#define CSCHED_FLAG_VCPU_PARKED    0x0001  /* VCPU over capped credits */
+#define CSCHED_FLAG_VCPU_YIELD     0x0002  /* VCPU yielding */
+#define CSCHED_FLAG_VCPU_YIELD_PRI 0x0004  /* VCPU's priority reduced to force a yield */
 
 
 /*
@@ -711,6 +713,15 @@ csched_vcpu_wake(struct vcpu *vc)
     __runq_tickle(cpu, svc);
 }
 
+static void
+csched_vcpu_yield(struct vcpu *v) 
+{
+    struct csched_vcpu * const sv = CSCHED_VCPU(v);
+
+    /* Temporarily lower priority of vcpus that yield */
+    sv->flags |= CSCHED_FLAG_VCPU_YIELD;
+}
+
 static int
 csched_dom_cntl(
     struct domain *d,
@@ -1231,12 +1242,38 @@ csched_schedule(s_time_t now)
     /*
      * Select next runnable local VCPU (ie top of local runq)
      */
+retry:
     if ( vcpu_runnable(current) )
         __runq_insert(cpu, scurr);
     else
         BUG_ON( is_idle_vcpu(current) || list_empty(runq) );
 
     snext = __runq_elem(runq->next);
+
+    /*
+     * Check to see if yield worked; if not, temporarily reduce priority
+     */
+    if ( scurr->flags & CSCHED_FLAG_VCPU_YIELD )
+    {
+        scurr->flags &= ~(CSCHED_FLAG_VCPU_YIELD);
+        /* Check to see if yield worked.  If not, reduce priority and retry. */
+        if ( (snext == scurr)
+            && (scurr->pri > CSCHED_PRI_TS_OVER) )
+        {
+            __runq_remove(scurr);
+            scurr->flags |= CSCHED_FLAG_VCPU_YIELD_PRI;
+            scurr->pri = CSCHED_PRI_TS_OVER;
+            goto retry;
+        }
+    }
+
+    /* If we reduced priority due to yielding, reinstate it. */
+    if ( snext->flags & CSCHED_FLAG_VCPU_YIELD_PRI )
+    {
+        snext->flags &= ~CSCHED_FLAG_VCPU_YIELD_PRI;
+        if ( snext->pri == CSCHED_PRI_TS_OVER )
+            snext->pri = CSCHED_PRI_TS_UNDER;
+    }
 
     /*
      * SMP Load balance:
@@ -1448,6 +1485,7 @@ struct scheduler sched_credit_def = {
 
     .sleep          = csched_vcpu_sleep,
     .wake           = csched_vcpu_wake,
+    .yield          = csched_vcpu_yield,
 
     .adjust         = csched_dom_cntl,
 
diff -r bb9a7d40d0b5 xen/common/schedule.c
--- a/xen/common/schedule.c	Mon Sep 01 13:01:23 2008 +0100
+++ b/xen/common/schedule.c	Mon Sep 01 13:01:25 2008 +0100
@@ -386,6 +386,12 @@ static long do_poll(struct sched_poll *s
 /* Voluntarily yield the processor for this allocation. */
 static long do_yield(void)
 {
+    struct vcpu * v=current;
+
+    vcpu_schedule_lock_irq(v);
+    SCHED_OP(yield, current);
+    vcpu_schedule_unlock_irq(v);
+
     TRACE_2D(TRC_SCHED_YIELD, current->domain->domain_id, current->vcpu_id);
     raise_softirq(SCHEDULE_SOFTIRQ);
     return 0;
diff -r bb9a7d40d0b5 xen/include/xen/sched-if.h
--- a/xen/include/xen/sched-if.h	Mon Sep 01 13:01:23 2008 +0100
+++ b/xen/include/xen/sched-if.h	Mon Sep 01 13:01:25 2008 +0100
@@ -69,6 +69,7 @@ struct scheduler {
 
     void         (*sleep)          (struct vcpu *);
     void         (*wake)           (struct vcpu *);
+    void         (*yield)          (struct vcpu *);
 
     struct task_slice (*do_schedule) (s_time_t);