[Xen-devel] [PATCH v1 2/5] xen: sched: null: don't assign down vcpus to 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.

So, avoid doing that while inserting or migrating vcpus.

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 |   26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/xen/common/sched_null.c b/xen/common/sched_null.c
index f372172c32..1426124525 100644
--- a/xen/common/sched_null.c
+++ b/xen/common/sched_null.c
@@ -340,6 +340,8 @@ static unsigned int pick_cpu(struct null_private *prv, 
struct vcpu *v)
 static void vcpu_assign(struct null_private *prv, struct vcpu *v,
                         unsigned int cpu)
 {
+    ASSERT(is_vcpu_online(v));
+
     per_cpu(npc, cpu).vcpu = v;
     v->processor = cpu;
     cpumask_clear_cpu(cpu, &prv->cpus_free);
@@ -454,8 +456,14 @@ static void null_vcpu_insert(const struct scheduler *ops, 
struct vcpu *v)
     ASSERT(!is_idle_vcpu(v));
 
     lock = vcpu_schedule_lock_irq(v);
- retry:
 
+    if ( unlikely(!is_vcpu_online(v)) )
+    {
+        vcpu_schedule_unlock_irq(lock, v);
+        return;
+    }
+
+ retry:
     cpu = v->processor = pick_cpu(prv, v);
 
     spin_unlock(lock);
@@ -617,6 +625,21 @@ static void null_vcpu_migrate(const struct scheduler *ops, 
struct vcpu *v,
 
     SCHED_STAT_CRANK(migrated);
 
+    /*
+     * If it was/it's going offline, we don't want it neither assigned to
+     * a vcpu, nor in the waitqueue.
+     *
+     * If it was on a cpu, we've removed it from there above. If it is in the
+     * waitqueue, we remove it from there now. And then we bail.
+     */
+    if ( unlikely(!is_vcpu_online(v)) )
+    {
+        spin_lock(&prv->waitq_lock);
+        list_del_init(&nvc->waitq_elem);
+        spin_unlock(&prv->waitq_lock);
+        goto out;
+    }
+
     /*
      * Let's now consider new_cpu, which is where v is being sent. It can be
      * either free, or have a vCPU already assigned to it.
@@ -657,6 +680,7 @@ static void null_vcpu_migrate(const struct scheduler *ops, 
struct vcpu *v,
      * at least. In case of suspend, any temporary inconsistency caused
      * by this, will be fixed-up during resume.
      */
+ out:
     v->processor = new_cpu;
 }
 


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