scheduler: Add a per-scheduler yield callback

Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>

xen/common/schedule.c

@@ -642,6 +642,12 @@ static long do_poll(struct sched_poll *sched_poll)
 /* Voluntarily yield the processor for this allocation. */
 static long do_yield(void)
 {
+    struct vcpu * v=current;
+
+    vcpu_schedule_lock_irq(v);
+    SCHED_OP(VCPU2OP(v), yield, v);
+    vcpu_schedule_unlock_irq(v);
+
     TRACE_2D(TRC_SCHED_YIELD, current->domain->domain_id, current->vcpu_id);
     raise_softirq(SCHEDULE_SOFTIRQ);
     return 0;

xen/include/xen/sched-if.h

@@ -107,6 +107,7 @@ struct scheduler {
 
     void         (*sleep)          (const struct scheduler *, struct vcpu *);
     void         (*wake)           (const struct scheduler *, struct vcpu *);
+    void         (*yield)          (const struct scheduler *, struct vcpu *);
     void         (*context_saved)  (const struct scheduler *, struct vcpu *);
 
     struct task_slice (*do_schedule) (const struct scheduler *, s_time_t,