File 5887888f-credit2-never-consider-CPUs-outside-of... of Package xen

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File 5887888f-credit2-never-consider-CPUs-outside-of-pool.patch of Package xen (Revision 6bbfc10fa0cd4906a4b565a5ad40b57f)

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# Commit e7191920261d20e52ca4c06a03589a1155981b04
# Date 2017-01-24 17:02:07 +0000
# Author Dario Faggioli <dario.faggioli@citrix.com>
# Committer George Dunlap <george.dunlap@citrix.com>
xen: credit2: never consider CPUs outside of our cpupool.

In fact, relying on the mask of what pCPUs belong to
which Credit2 runqueue is not enough. If we only do that,
when Credit2 is the boot scheduler, we may ASSERT() or
panic when moving a pCPU from Pool-0 to another cpupool.

This is because pCPUs outside of any pool are considered
part of cpupool0. This puts us at risk of crash when those
same pCPUs are added to another pool and something
different than the idle domain is found to be running
on them.

Note that, even if we prevent the above to happen (which
is the purpose of this patch), this is still pretty bad,
in fact, when we remove a pCPU from Pool-0:
- in Credit1, as we do *not* update prv->ncpus and
  prv->credit, which means we're considering the wrong
  total credits when doing accounting;
- in Credit2, the pCPU remains part of one runqueue,
  and is hence at least considered during load balancing,
  even if no vCPU should really run there.

In Credit1, this "only" causes skewed accounting and
no crashes because there is a lot of `cpumask_and`ing
going on with the cpumask of the domains' cpupool
(which, BTW, comes at a price).

A quick and not to involved (and easily backportable)
solution for Credit2, is to do exactly the same.

Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com
Acked-by: George Dunlap <george.dunlap@citrix.com>

--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -510,19 +510,22 @@ void smt_idle_mask_clear(unsigned int cp
  */
 static int get_fallback_cpu(struct csched2_vcpu *svc)
 {
-    int fallback_cpu, cpu = svc->vcpu->processor;
+    struct vcpu *v = svc->vcpu;
+    int cpu = v->processor;
 
-    if ( likely(cpumask_test_cpu(cpu, svc->vcpu->cpu_hard_affinity)) )
-        return cpu;
+    cpumask_and(cpumask_scratch_cpu(cpu), v->cpu_hard_affinity,
+                cpupool_domain_cpumask(v->domain));
 
-    cpumask_and(cpumask_scratch_cpu(cpu), svc->vcpu->cpu_hard_affinity,
-                &svc->rqd->active);
-    fallback_cpu = cpumask_first(cpumask_scratch_cpu(cpu));
-    if ( likely(fallback_cpu < nr_cpu_ids) )
-        return fallback_cpu;
+    if ( likely(cpumask_test_cpu(cpu, cpumask_scratch_cpu(cpu))) )
+        return cpu;
 
-    cpumask_and(cpumask_scratch, svc->vcpu->cpu_hard_affinity,
-                cpupool_domain_cpumask(svc->vcpu->domain));
+    if ( likely(cpumask_intersects(cpumask_scratch_cpu(cpu),
+                                   &svc->rqd->active)) )
+    {
+        cpumask_and(cpumask_scratch_cpu(cpu), &svc->rqd->active,
+                    cpumask_scratch_cpu(cpu));
+        return cpumask_first(cpumask_scratch_cpu(cpu));
+    }
 
     ASSERT(!cpumask_empty(cpumask_scratch_cpu(cpu)));
 
@@ -940,6 +943,9 @@ runq_tickle(const struct scheduler *ops,
                     (unsigned char *)&d);
     }
 
+    cpumask_and(cpumask_scratch_cpu(cpu), new->vcpu->cpu_hard_affinity,
+                cpupool_domain_cpumask(new->vcpu->domain));
+
     /*
      * First of all, consider idle cpus, checking if we can just
      * re-use the pcpu where we were running before.
@@ -952,7 +958,7 @@ runq_tickle(const struct scheduler *ops,
         cpumask_andnot(&mask, &rqd->idle, &rqd->smt_idle);
     else
         cpumask_copy(&mask, &rqd->smt_idle);
-    cpumask_and(&mask, &mask, new->vcpu->cpu_hard_affinity);
+    cpumask_and(&mask, &mask, cpumask_scratch_cpu(cpu));
     i = cpumask_test_or_cycle(cpu, &mask);
     if ( i < nr_cpu_ids )
     {
@@ -967,7 +973,7 @@ runq_tickle(const struct scheduler *ops,
      * gone through the scheduler yet.
      */
     cpumask_andnot(&mask, &rqd->idle, &rqd->tickled);
-    cpumask_and(&mask, &mask, new->vcpu->cpu_hard_affinity);
+    cpumask_and(&mask, &mask, cpumask_scratch_cpu(cpu));
     i = cpumask_test_or_cycle(cpu, &mask);
     if ( i < nr_cpu_ids )
     {
@@ -983,7 +989,7 @@ runq_tickle(const struct scheduler *ops,
      */
     cpumask_andnot(&mask, &rqd->active, &rqd->idle);
     cpumask_andnot(&mask, &mask, &rqd->tickled);
-    cpumask_and(&mask, &mask, new->vcpu->cpu_hard_affinity);
+    cpumask_and(&mask, &mask, cpumask_scratch_cpu(cpu));
     if ( cpumask_test_cpu(cpu, &mask) )
     {
         cur = CSCHED2_VCPU(curr_on_cpu(cpu));
@@ -1525,6 +1531,9 @@ csched2_cpu_pick(const struct scheduler
         goto out;
     }
 
+    cpumask_and(cpumask_scratch_cpu(cpu), vc->cpu_hard_affinity,
+                cpupool_domain_cpumask(vc->domain));
+
     /*
      * First check to see if we're here because someone else suggested a place
      * for us to move.
@@ -1536,13 +1545,13 @@ csched2_cpu_pick(const struct scheduler
             printk(XENLOG_WARNING "%s: target runqueue disappeared!\n",
                    __func__);
         }
-        else
+        else if ( cpumask_intersects(cpumask_scratch_cpu(cpu),
+                                     &svc->migrate_rqd->active) )
         {
-            cpumask_and(cpumask_scratch_cpu(cpu), vc->cpu_hard_affinity,
+            cpumask_and(cpumask_scratch_cpu(cpu), cpumask_scratch_cpu(cpu),
                         &svc->migrate_rqd->active);
             new_cpu = cpumask_any(cpumask_scratch_cpu(cpu));
-            if ( new_cpu < nr_cpu_ids )
-                goto out_up;
+            goto out_up;
         }
         /* Fall-through to normal cpu pick */
     }
@@ -1570,12 +1579,12 @@ csched2_cpu_pick(const struct scheduler
          */
         if ( rqd == svc->rqd )
         {
-            if ( cpumask_intersects(vc->cpu_hard_affinity, &rqd->active) )
+            if ( cpumask_intersects(cpumask_scratch_cpu(cpu), &rqd->active) )
                 rqd_avgload = max_t(s_time_t, rqd->b_avgload - svc->avgload, 0);
         }
         else if ( spin_trylock(&rqd->lock) )
         {
-            if ( cpumask_intersects(vc->cpu_hard_affinity, &rqd->active) )
+            if ( cpumask_intersects(cpumask_scratch_cpu(cpu), &rqd->active) )
                 rqd_avgload = rqd->b_avgload;
 
             spin_unlock(&rqd->lock);
@@ -1597,7 +1606,7 @@ csched2_cpu_pick(const struct scheduler
         goto out_up;
     }
 
-    cpumask_and(cpumask_scratch_cpu(cpu), vc->cpu_hard_affinity,
+    cpumask_and(cpumask_scratch_cpu(cpu), cpumask_scratch_cpu(cpu),
                 &prv->rqd[min_rqi].active);
     new_cpu = cpumask_any(cpumask_scratch_cpu(cpu));
     BUG_ON(new_cpu >= nr_cpu_ids);
@@ -1713,6 +1722,8 @@ static void migrate(const struct schedul
         __runq_deassign(svc);
 
         cpumask_and(cpumask_scratch_cpu(cpu), svc->vcpu->cpu_hard_affinity,
+                    cpupool_domain_cpumask(svc->vcpu->domain));
+        cpumask_and(cpumask_scratch_cpu(cpu), cpumask_scratch_cpu(cpu),
                     &trqd->active);
         svc->vcpu->processor = cpumask_any(cpumask_scratch_cpu(cpu));
         ASSERT(svc->vcpu->processor < nr_cpu_ids);
@@ -1738,8 +1749,14 @@ static void migrate(const struct schedul
 static bool_t vcpu_is_migrateable(struct csched2_vcpu *svc,
                                   struct csched2_runqueue_data *rqd)
 {
+    struct vcpu *v = svc->vcpu;
+    int cpu = svc->vcpu->processor;
+
+    cpumask_and(cpumask_scratch_cpu(cpu), v->cpu_hard_affinity,
+                cpupool_domain_cpumask(v->domain));
+
     return !(svc->flags & CSFLAG_runq_migrate_request) &&
-           cpumask_intersects(svc->vcpu->cpu_hard_affinity, &rqd->active);
+           cpumask_intersects(cpumask_scratch_cpu(cpu), &rqd->active);
 }
 
 static void balance_load(const struct scheduler *ops, int cpu, s_time_t now)

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File 5887888f-credit2-never-consider-CPUs-outside-of-pool.patch of Package xen (Revision 6bbfc10fa0cd4906a4b565a5ad40b57f)

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