credit2: add a callback to migrate to a new cpu

In credit2, there needs to be a strong correlation between
v->processor and the runqueue to which a vcpu is assigned;
much of the code relies on this invariant.  Allow credit2
to manage the actual migration itself.

This fixes the most recent credit2 bug reported on the list
(Xen BUG at sched_credit2.c:1606) in Xen 4.1, as well as
the bug at sched_credit2.c:811 in -unstable (which catches the
same condition earlier).

Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>
xen-unstable changeset:   23250:7745109e3c6e
xen-unstable date:        Wed Apr 27 13:36:15 2011 +0100

diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
index 9924b092441e08c43e477799748fce59c3218577..aed1d44840c533623395c6e23ca1d20c5a46cce5 100644 (file)
--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -1351,32 +1351,29 @@ out:
 static int
 csched_cpu_pick(const struct scheduler *ops, struct vcpu *vc)
 {
-    struct csched_vcpu * const svc = CSCHED_VCPU(vc);
     int new_cpu;
 
-    /* The scheduler interface doesn't have an explicit mechanism to
-     * involve the choosable scheduler in the migrate process, so we
-     * infer that a change may happen by the call to cpu_pick, and
-     * remove it from the old runqueue while the lock for the old
-     * runqueue is held.  It can't be actively waiting to run.  It
-     * will be added to the new runqueue when it next wakes.
-     *
-     * If we want to be able to call pick() separately, we need to add
-     * a mechansim to remove a vcpu from an old processor / runqueue
-     * before releasing the lock. */
-    BUG_ON(__vcpu_on_runq(svc));
-
     new_cpu = choose_cpu(ops, vc);
-    /* If we're suggesting moving to a different runqueue, remove it
-     * from the old runqueue while we have the lock.  It will be added
-     * to the new one when it wakes. */
-    if ( svc->rqd != NULL
-         && RQD(ops, new_cpu) != svc->rqd )
-        runq_deassign(ops, vc);
 
     return new_cpu;
 }
 
+static void
+csched_vcpu_migrate(
+    const struct scheduler *ops, struct vcpu *vc, unsigned int new_cpu)
+{
+    struct csched_vcpu * const svc = CSCHED_VCPU(vc);
+    struct csched_runqueue_data *trqd;
+
+    /* Check if new_cpu is valid */
+    BUG_ON(!cpu_isset(new_cpu, CSCHED_PRIV(ops)->initialized));
+
+    trqd = RQD(ops, new_cpu);
+
+    if ( trqd != svc->rqd )
+        migrate(ops, svc, trqd, NOW());
+}
+
 static int
 csched_dom_cntl(
     const struct scheduler *ops,
@@ -2089,6 +2086,7 @@ const struct scheduler sched_credit2_def = {
     .adjust         = csched_dom_cntl,
 
     .pick_cpu       = csched_cpu_pick,
+    .migrate        = csched_vcpu_migrate,
     .do_schedule    = csched_schedule,
     .context_saved  = csched_context_saved,
 

diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index 129abe44e4b3c0a44ab903842c3e41632413eb1a..53a1353b47150e05ebe04681d0e797e4c194a8d4 100644 (file)
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -490,7 +490,11 @@ static void vcpu_migrate(struct vcpu *v)
      * Switch to new CPU, then unlock new and old CPU.  This is safe because
      * the lock pointer cant' change while the current lock is held.
      */
-    v->processor = new_cpu;
+    if ( VCPU2OP(v)->migrate )
+        SCHED_OP(VCPU2OP(v), migrate, v, new_cpu);
+    else
+        v->processor = new_cpu;
+
 
     if ( old_lock != new_lock )
         spin_unlock(new_lock);

diff --git a/xen/include/xen/sched-if.h b/xen/include/xen/sched-if.h
index e8f0262a6bf15f968be67e20a309ef12a36ba98d..702910b1b2a16e06e3fb0e23483fc4b2de2697f6 100644 (file)
--- a/xen/include/xen/sched-if.h
+++ b/xen/include/xen/sched-if.h
@@ -168,6 +168,8 @@ struct scheduler {
                                       bool_t tasklet_work_scheduled);
 
     int          (*pick_cpu)       (const struct scheduler *, struct vcpu *);
+    void         (*migrate)        (const struct scheduler *, struct vcpu *,
+                                    unsigned int);
     int          (*adjust)         (const struct scheduler *, struct domain *,
                                     struct xen_domctl_scheduler_op *);
     int          (*adjust_global)  (const struct scheduler *,