xen: rtds: only tickle non-already tickled CPUs

When more than one idle VCPUs that have the same PCPU as their
previous running core invoke runq_tickle(), they will tickle the same
PCPU. The tickled PCPU will only pick at most one VCPU, i.e., the
highest-priority one, to execute. The other VCPUs will not be
scheduled for a period, even when there is an idle core, making these
VCPUs unnecessarily starve for one period.

Therefore, always make sure that we only tickle PCPUs that have not
been tickled already.

Signed-off-by: Haoran Li <naroahlee@gmail.com>
Signed-off-by: Meng Xu <mengxu@cis.upenn.edu>
Reviewed-by: Dario Faggioli <dario.faggioli@citrix.com>

diff --git a/xen/common/sched_rt.c b/xen/common/sched_rt.c
index 39f6bee47a3a18760aa3e43dbb202b6db70fbc9d..0ac58168f84f923b0f5d6055f7b97d1c363a6efe 100644 (file)
--- a/xen/common/sched_rt.c
+++ b/xen/common/sched_rt.c
@@ -1147,9 +1147,9 @@ rt_vcpu_sleep(const struct scheduler *ops, struct vcpu *vc)
  * Called by wake() and context_saved()
  * We have a running candidate here, the kick logic is:
  * Among all the cpus that are within the cpu affinity
- * 1) if the new->cpu is idle, kick it. This could benefit cache hit
- * 2) if there are any idle vcpu, kick it.
- * 3) now all pcpus are busy;
+ * 1) if there are any idle CPUs, kick one.
+      For cache benefit, we check new->cpu as first
+ * 2) now all pcpus are busy;
  *    among all the running vcpus, pick lowest priority one
  *    if snext has higher priority, kick it.
  *
@@ -1177,17 +1177,13 @@ runq_tickle(const struct scheduler *ops, struct rt_vcpu *new)
     cpumask_and(&not_tickled, online, new->vcpu->cpu_hard_affinity);
     cpumask_andnot(&not_tickled, &not_tickled, &prv->tickled);
 
-    /* 1) if new's previous cpu is idle, kick it for cache benefit */
-    if ( is_idle_vcpu(curr_on_cpu(new->vcpu->processor)) )
-    {
-        SCHED_STAT_CRANK(tickled_idle_cpu);
-        cpu_to_tickle = new->vcpu->processor;
-        goto out;
-    }
-
-    /* 2) if there are any idle pcpu, kick it */
-    /* The same loop also find the one with lowest priority */
-    for_each_cpu(cpu, &not_tickled)
+    /*
+     * 1) If there are any idle CPUs, kick one.
+     *    For cache benefit,we first search new->cpu.
+     *    The same loop also find the one with lowest priority.
+     */
+    cpu = cpumask_test_or_cycle(new->vcpu->processor, &not_tickled);
+    while ( cpu!= nr_cpu_ids )
     {
         iter_vc = curr_on_cpu(cpu);
         if ( is_idle_vcpu(iter_vc) )
@@ -1200,9 +1196,12 @@ runq_tickle(const struct scheduler *ops, struct rt_vcpu *new)
         if ( latest_deadline_vcpu == NULL ||
              iter_svc->cur_deadline > latest_deadline_vcpu->cur_deadline )
             latest_deadline_vcpu = iter_svc;
+
+        cpumask_clear_cpu(cpu, &not_tickled);
+        cpu = cpumask_cycle(cpu, &not_tickled);
     }
 
-    /* 3) candicate has higher priority, kick out lowest priority vcpu */
+    /* 2) candicate has higher priority, kick out lowest priority vcpu */
     if ( latest_deadline_vcpu != NULL &&
          new->cur_deadline < latest_deadline_vcpu->cur_deadline )
     {