sched: better handle (not) inserting idle vCPUs in runqueues

Idle vCPUs are set to run immediately, as a part of their
own initialization, so we shouldn't even try to put them
in a runqueue. In fact, no scheduler does that, even when
asked to (that is rather explicit in Credit2 and RTDS, a
bit less evident in Credit1).

Let's make things look as follows:
 - in generic code, explicitly avoid even trying to
   insert idle vCPUs in runqueues;
 - in specific schedulers' code, enforce that.

Note that, as csched_vcpu_insert() is no longer being
called, during boot (from sched_init_vcpu()) we can
safely avoid saving the flags when taking the runqueue
lock.

Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
Acked-by: George Dunlap <george.dunlap@eu.citrix.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
master commit: 6b53bb4ab3c9bd5eccde88a5175cf72589ba6d52
master date: 2015-11-24 14:49:47 +0100

diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c
index 54fd830efba0f5d61f49fb14c455fd91604117c9..8a20f08dd16bf12e95e7c6d03360c4e0d08eeae4 100644 (file)
--- a/xen/common/sched_credit.c
+++ b/xen/common/sched_credit.c
@@ -890,14 +890,15 @@ csched_vcpu_insert(const struct scheduler *ops, struct vcpu *vc)
 {
     struct csched_vcpu *svc = vc->sched_priv;
     spinlock_t *lock;
-    unsigned long flags;
 
-    lock = vcpu_schedule_lock_irqsave(vc, &flags);
+    BUG_ON( is_idle_vcpu(vc) );
+
+    lock = vcpu_schedule_lock_irq(vc);
 
     if ( !__vcpu_on_runq(svc) && vcpu_runnable(vc) && !vc->is_running )
         __runq_insert(vc->processor, svc);
 
-    vcpu_schedule_unlock_irqrestore(lock, flags, vc);
+    vcpu_schedule_unlock_irq(lock, vc);
 }
 
 static void

diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
index db9e1c4a104dde90102ca62238b12fa36c04aa8b..2ab030476f9b86df9a16d48bbde199f18507b8c6 100644 (file)
--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -861,28 +861,23 @@ csched2_vcpu_insert(const struct scheduler *ops, struct vcpu *vc)
 {
     struct csched2_vcpu *svc = vc->sched_priv;
     struct csched2_dom * const sdom = svc->sdom;
+    spinlock_t *lock;
 
     printk("%s: Inserting %pv\n", __func__, vc);
 
-    /* NB: On boot, idle vcpus are inserted before alloc_pdata() has
-     * been called for that cpu.
-     */
-    if ( ! is_idle_vcpu(vc) )
-    {
-        spinlock_t *lock;
+    BUG_ON(is_idle_vcpu(vc));
 
-        /* FIXME: Do we need the private lock here? */
-        list_add_tail(&svc->sdom_elem, &svc->sdom->vcpu);
+    /* FIXME: Do we need the private lock here? */
+    list_add_tail(&svc->sdom_elem, &svc->sdom->vcpu);
 
-        /* Add vcpu to runqueue of initial processor */
-        lock = vcpu_schedule_lock_irq(vc);
+    /* Add vcpu to runqueue of initial processor */
+    lock = vcpu_schedule_lock_irq(vc);
 
-        runq_assign(ops, vc);
+    runq_assign(ops, vc);
 
-        vcpu_schedule_unlock_irq(lock, vc);
+    vcpu_schedule_unlock_irq(lock, vc);
 
-        sdom->nr_vcpus++;
-    }
+    sdom->nr_vcpus++;
 
     CSCHED2_VCPU_CHECK(vc);
 }

diff --git a/xen/common/sched_rt.c b/xen/common/sched_rt.c
index a77e80800a8cc0856b02ade52499590a3aa2a0c9..e50041c8ced245d5e2471d8e026eb07a7dca1374 100644 (file)
--- a/xen/common/sched_rt.c
+++ b/xen/common/sched_rt.c
@@ -550,9 +550,7 @@ rt_vcpu_insert(const struct scheduler *ops, struct vcpu *vc)
     s_time_t now;
     spinlock_t *lock;
 
-    /* not addlocate idle vcpu to dom vcpu list */
-    if ( is_idle_vcpu(vc) )
-        return;
+    BUG_ON( is_idle_vcpu(vc) );
 
     lock = vcpu_schedule_lock_irq(vc);
 

diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index 3e30047a4a72ff14956169d8aea820125b568569..1505d6dfd39c3384f0a96636e1e0c4e91a846745 100644 (file)
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -209,20 +209,22 @@ int sched_init_vcpu(struct vcpu *v, unsigned int processor)
     init_timer(&v->poll_timer, poll_timer_fn,
                v, v->processor);
 
-    /* Idle VCPUs are scheduled immediately. */
+    v->sched_priv = SCHED_OP(DOM2OP(d), alloc_vdata, v, d->sched_priv);
+    if ( v->sched_priv == NULL )
+        return 1;
+
+    TRACE_2D(TRC_SCHED_DOM_ADD, v->domain->domain_id, v->vcpu_id);
+
+    /* Idle VCPUs are scheduled immediately, so don't put them in runqueue. */
     if ( is_idle_domain(d) )
     {
         per_cpu(schedule_data, v->processor).curr = v;
         v->is_running = 1;
     }
-
-    TRACE_2D(TRC_SCHED_DOM_ADD, v->domain->domain_id, v->vcpu_id);
-
-    v->sched_priv = SCHED_OP(DOM2OP(d), alloc_vdata, v, d->sched_priv);
-    if ( v->sched_priv == NULL )
-        return 1;
-
-    SCHED_OP(DOM2OP(d), insert_vcpu, v);
+    else
+    {
+        SCHED_OP(DOM2OP(d), insert_vcpu, v);
+    }
 
     return 0;
 }