xen/sched: build a linked list of struct sched_unit

In order to make it easy to iterate over sched_unit elements of a
domain, build a single linked list and add an iterator for it. The new
list is guarded by the same mechanisms as the vcpu linked list as it
is modified only via vcpu_create() or vcpu_destroy().

For completeness add another iterator for_each_sched_unit_vcpu() which
will iterate over all vcpus of a sched_unit (right now only one). This
will be needed later for larger scheduling granularity (e.g. cores).

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Dario Faggioli <dfaggioli@suse.com>

xen/common/schedule.c

@@ -305,6 +305,55 @@ static void sched_spin_unlock_double(spinlock_t *lock1, spinlock_t *lock2,
     spin_unlock_irqrestore(lock1, flags);
 }
 
+static void sched_free_unit(struct sched_unit *unit)
+{
+    struct sched_unit *prev_unit;
+    struct domain *d = unit->domain;
+
+    if ( d->sched_unit_list == unit )
+        d->sched_unit_list = unit->next_in_list;
+    else
+    {
+        for_each_sched_unit ( d, prev_unit )
+        {
+            if ( prev_unit->next_in_list == unit )
+            {
+                prev_unit->next_in_list = unit->next_in_list;
+                break;
+            }
+        }
+    }
+
+    unit->vcpu_list->sched_unit = NULL;
+    xfree(unit);
+}
+
+static struct sched_unit *sched_alloc_unit(struct vcpu *v)
+{
+    struct sched_unit *unit, **prev_unit;
+    struct domain *d = v->domain;
+
+    if ( (unit = xzalloc(struct sched_unit)) == NULL )
+        return NULL;
+
+    unit->vcpu_list = v;
+    unit->unit_id = v->vcpu_id;
+    unit->domain = d;
+
+    for ( prev_unit = &d->sched_unit_list; *prev_unit;
+          prev_unit = &(*prev_unit)->next_in_list )
+        if ( (*prev_unit)->next_in_list &&
+             (*prev_unit)->next_in_list->unit_id > unit->unit_id )
+            break;
+
+    unit->next_in_list = *prev_unit;
+    *prev_unit = unit;
+
+    v->sched_unit = unit;
+
+    return unit;
+}
+
 int sched_init_vcpu(struct vcpu *v, unsigned int processor)
 {
     struct domain *d = v->domain;
@@ -312,11 +361,8 @@ int sched_init_vcpu(struct vcpu *v, unsigned int processor)
 
     v->processor = processor;
 
-    if ( (unit = xzalloc(struct sched_unit)) == NULL )
+    if ( (unit = sched_alloc_unit(v)) == NULL )
         return 1;
-    unit->vcpu_list = v;
-    unit->unit_id = v->vcpu_id;
-    unit->domain = d;
 
     /* Initialise the per-vcpu timers. */
     spin_lock_init(&v->periodic_timer_lock);
@@ -330,12 +376,10 @@ int sched_init_vcpu(struct vcpu *v, unsigned int processor)
     unit->priv = sched_alloc_udata(dom_scheduler(d), unit, d->sched_priv);
     if ( unit->priv == NULL )
     {
-        xfree(unit);
+        sched_free_unit(unit);
         return 1;
     }
 
-    v->sched_unit = unit;
-
     /*
      * Initialize affinity settings. The idler, and potentially
      * domain-0 VCPUs, are pinned onto their respective physical CPUs.
@@ -475,8 +519,7 @@ void sched_destroy_vcpu(struct vcpu *v)
         atomic_dec(&per_cpu(schedule_data, v->processor).urgent_count);
     sched_remove_unit(vcpu_scheduler(v), unit);
     sched_free_udata(vcpu_scheduler(v), unit->priv);
-    v->sched_unit = NULL;
-    xfree(unit);
+    sched_free_unit(unit);
 }
 
 int sched_init_domain(struct domain *d, int poolid)

xen/include/xen/sched.h

@@ -277,9 +277,24 @@ struct sched_unit {
     struct domain         *domain;
     struct vcpu           *vcpu_list;
     void                  *priv;      /* scheduler private data */
+    struct sched_unit     *next_in_list;
     unsigned int           unit_id;
 };
 
+#define for_each_sched_unit(d, u)                                         \
+    for ( (u) = (d)->sched_unit_list; (u) != NULL; (u) = (u)->next_in_list )
+
+/*
+ * All vcpus of a domain are in a single linked list with unit->vcpu_list
+ * pointing to the first vcpu of the unit. The loop must be terminated when
+ * a vcpu is hit not being part of the unit to loop over.
+ */
+#define for_each_sched_unit_vcpu(u, v)                                    \
+    for ( (v) = (u)->vcpu_list;                                           \
+          (v) != NULL && (!(u)->next_in_list ||                           \
+                          (v)->vcpu_id < (u)->next_in_list->unit_id);     \
+          (v) = (v)->next_in_list )
+
 /* Per-domain lock can be recursively acquired in fault handlers. */
 #define domain_lock(d) spin_lock_recursive(&(d)->domain_lock)
 #define domain_unlock(d) spin_unlock_recursive(&(d)->domain_lock)
@@ -333,6 +348,7 @@ struct domain
 
     /* Scheduling. */
     void            *sched_priv;    /* scheduler-specific data */
+    struct sched_unit *sched_unit_list;
     struct cpupool  *cpupool;
 
     struct domain   *next_in_list;