credit2: Track expected load

As vcpus are migrated, track how we expect the load to change.  This
helps smooth migrations when the balancing doesn't take immediate
effect on the load average.  In theory, if vcpu activity remains
constant, then the measured avgload should converge to the balanced
avgload.

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

1 files changed, 14 insertions, 1 deletions

diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
index 58f146cc99..6d79a72893 100644
--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -206,6 +206,7 @@ struct csched_runqueue_data {
     int load;              /* Instantaneous load: Length of queue  + num non-idle threads */
     s_time_t load_last_update;  /* Last time average was updated */
     s_time_t avgload;           /* Decaying queue load */
+    s_time_t b_avgload;         /* Decaying queue load modified by balancing */
 };
 
 /*
@@ -302,6 +303,7 @@ __update_runq_load(const struct scheduler *ops,
     if ( rqd->load_last_update + (1ULL<<prv->load_window_shift) < now )
     {
         rqd->avgload = (unsigned long long)rqd->load << prv->load_window_shift;
+        rqd->b_avgload = (unsigned long long)rqd->load << prv->load_window_shift;
     }
     else
     {
@@ -310,6 +312,10 @@ __update_runq_load(const struct scheduler *ops,
         rqd->avgload =
             ( ( delta * ( (unsigned long long)rqd->load << prv->load_window_shift ) )
               + ( ((1ULL<<prv->load_window_shift) - delta) * rqd->avgload ) ) >> prv->load_window_shift;
+
+        rqd->b_avgload =
+            ( ( delta * ( (unsigned long long)rqd->load << prv->load_window_shift ) )
+              + ( ((1ULL<<prv->load_window_shift) - delta) * rqd->b_avgload ) ) >> prv->load_window_shift;
     }
     rqd->load += change;
     rqd->load_last_update = now;
@@ -317,11 +323,12 @@ __update_runq_load(const struct scheduler *ops,
     {
         struct {
             unsigned rq_load:4, rq_avgload:28;
-            unsigned rq_id:4;
+            unsigned rq_id:4, b_avgload:28;
         } d;
         d.rq_id=rqd->id;
         d.rq_load = rqd->load;
         d.rq_avgload = rqd->avgload;
+        d.b_avgload = rqd->b_avgload;
         trace_var(TRC_CSCHED2_UPDATE_RUNQ_LOAD, 1,
                   sizeof(d),
                   (unsigned char *)&d);
@@ -756,6 +763,9 @@ __runq_assign(struct csched_vcpu *svc, struct csched_runqueue_data *rqd)
 
     update_max_weight(svc->rqd, svc->weight, 0);
 
+    /* Expected new load based on adding this vcpu */
+    rqd->b_avgload += svc->avgload;
+
     /* TRACE */
     {
         struct {
@@ -790,6 +800,9 @@ __runq_deassign(struct csched_vcpu *svc)
     list_del_init(&svc->rqd_elem);
     update_max_weight(svc->rqd, 0, svc->weight);
 
+    /* Expected new load based on removing this vcpu */
+    svc->rqd->b_avgload -= svc->avgload;
+
     svc->rqd = NULL;
 }