# HG changeset patch
# Parent 3a70bd1d02c1334857c84c9fb5e1dd22b6603a2c

diff -r 3a70bd1d02c1 xen/common/sched_credit.c
--- a/xen/common/sched_credit.c	Thu Nov 15 18:22:56 2012 +0100
+++ b/xen/common/sched_credit.c	Thu Nov 15 19:03:19 2012 +0100
@@ -274,7 +274,7 @@ static inline void
     }
 
     /*
-     * If this CPU has at least two runnable VCPUs, we tickle any idlers to
+     * If this CPU has at least two runnable VCPUs, we tickle some idlers to
      * let them know there is runnable work in the system...
      */
     if ( cur->pri > CSCHED_PRI_IDLE )
@@ -287,7 +287,17 @@ static inline void
         {
             cpumask_t idle_mask;
 
-            cpumask_and(&idle_mask, prv->idlers, new->vcpu->cpu_affinity);
+            /*
+             * Which idlers do we want to tickle? If new has higher priority,
+             * it will likely preempt cur and run here. We then need someone
+             * where cur can run to come and pick it up. Vice-versa, if it is
+             * cur that stays, we poke idlers where new can run.
+             */
+            if ( new->pri > cur->pri )
+                cpumask_and(&idle_mask, prv->idlers, cur->vcpu->cpu_affinity);
+            else
+                cpumask_and(&idle_mask, prv->idlers, new->vcpu->cpu_affinity);
+
             if ( !cpumask_empty(&idle_mask) )
             {
                 SCHED_STAT_CRANK(tickle_idlers_some);