[Xen-devel] [PATCH v1 3/5] xen: sched: null: deassign offline vcpus from pcpus

[Dario Faggioli <dfaggioli@xxxxxxxx>]

If a pCPU has been/is being offlined, we don't want it to be neither
assigned to any pCPU, nor in the wait list.

Therefore, when we detect that a vcpu is going offline, remove it from
both places.

Signed-off-by: Dario Faggioli <dfaggioli@xxxxxxxx>
---
Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Roger Pau Monne <roger.pau@xxxxxxxxxx>
---
 xen/common/sched_null.c |   43 +++++++++++++++++++++++++++++++++++++------
 1 file changed, 37 insertions(+), 6 deletions(-)

diff --git a/xen/common/sched_null.c b/xen/common/sched_null.c
index 1426124525..6259f4643e 100644
--- a/xen/common/sched_null.c
+++ b/xen/common/sched_null.c
@@ -361,7 +361,8 @@ static void vcpu_assign(struct null_private *prv, struct 
vcpu *v,
     }
 }
 
-static void vcpu_deassign(struct null_private *prv, struct vcpu *v)
+/* Returns true if a cpu was tickled */
+static bool vcpu_deassign(struct null_private *prv, struct vcpu *v)
 {
     unsigned int bs;
     unsigned int cpu = v->processor;
@@ -406,11 +407,13 @@ static void vcpu_deassign(struct null_private *prv, 
struct vcpu *v)
                 vcpu_assign(prv, wvc->vcpu, cpu);
                 cpu_raise_softirq(cpu, SCHEDULE_SOFTIRQ);
                 spin_unlock(&prv->waitq_lock);
-                return;
+                return true;
             }
         }
     }
     spin_unlock(&prv->waitq_lock);
+
+    return false;
 }
 
 /* Change the scheduler of cpu to us (null). */
@@ -518,6 +521,14 @@ static void null_vcpu_remove(const struct scheduler *ops, 
struct vcpu *v)
 
     lock = vcpu_schedule_lock_irq(v);
 
+    /* If offline, the vcpu shouldn't be assigned, nor in the waitqueue */
+    if ( unlikely(!is_vcpu_online(v)) )
+    {
+        ASSERT(per_cpu(npc, v->processor).vcpu != v);
+        ASSERT(list_empty(&nvc->waitq_elem));
+        goto out;
+    }
+
     /* If v is in waitqueue, just get it out of there and bail */
     if ( unlikely(!list_empty(&nvc->waitq_elem)) )
     {
@@ -567,11 +578,31 @@ static void null_vcpu_wake(const struct scheduler *ops, 
struct vcpu *v)
 
 static void null_vcpu_sleep(const struct scheduler *ops, struct vcpu *v)
 {
+    struct null_private *prv = null_priv(ops);
+    unsigned int cpu = v->processor;
+    bool tickled = false;
+
     ASSERT(!is_idle_vcpu(v));
 
+    /* We need to special case the handling of the vcpu being offlined */
+    if ( unlikely(!is_vcpu_online(v)) )
+    {
+        struct null_vcpu *nvc = null_vcpu(v);
+
+        printk("YYY d%dv%d going down?\n", v->domain->domain_id, v->vcpu_id);
+        if ( unlikely(!list_empty(&nvc->waitq_elem)) )
+        {
+            spin_lock(&prv->waitq_lock);
+            list_del_init(&nvc->waitq_elem);
+            spin_unlock(&prv->waitq_lock);
+        }
+        else if ( per_cpu(npc, cpu).vcpu == v )
+            tickled = vcpu_deassign(prv, v);
+    }
+
     /* If v is not assigned to a pCPU, or is not running, no need to bother */
-    if ( curr_on_cpu(v->processor) == v )
-        cpu_raise_softirq(v->processor, SCHEDULE_SOFTIRQ);
+    if ( likely(!tickled && curr_on_cpu(cpu) == v) )
+        cpu_raise_softirq(cpu, SCHEDULE_SOFTIRQ);
 
     SCHED_STAT_CRANK(vcpu_sleep);
 }
@@ -615,12 +646,12 @@ static void null_vcpu_migrate(const struct scheduler 
*ops, struct vcpu *v,
      *
      * In the latter, there is just nothing to do.
      */
-    if ( likely(list_empty(&nvc->waitq_elem)) )
+    if ( likely(per_cpu(npc, v->processor).vcpu == v) )
     {
         vcpu_deassign(prv, v);
         SCHED_STAT_CRANK(migrate_running);
     }
-    else
+    else if ( !list_empty(&nvc->waitq_elem) )
         SCHED_STAT_CRANK(migrate_on_runq);
 
     SCHED_STAT_CRANK(migrated);


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