fixup MPCP-VS: don't priority boost until after virtual spinning is over

Otherwise there is no benefit to the virtual spinning...

1 files changed, 32 insertions, 34 deletions

diff --git a/litmus/sched_pfp.c b/litmus/sched_pfp.c
index f5796f3607f4..74a77e7a4959 100644
--- a/litmus/sched_pfp.c
+++ b/litmus/sched_pfp.c
@@ -690,39 +690,42 @@ static void mpcp_vspin_enter(void)
 {
         struct task_struct* t = current;
 
-        if (__get_cpu_var(mpcpvs_vspin) == NULL) {
-                /* good, we get to issue our request */
-                __get_cpu_var(mpcpvs_vspin) = t;
-        } else {
-                /* some job is spinning => enqueue in request queue */
-                prio_wait_queue_t wait;
-                wait_queue_head_t* vspin = &__get_cpu_var(mpcpvs_vspin_wait);
-                unsigned long flags;
-
-                /* ordered by regular priority */
-                init_prio_waitqueue_entry(&wait, t, prio_point(get_priority(t)));
+        while (1) {
+                if (__get_cpu_var(mpcpvs_vspin) == NULL) {
+                        /* good, we get to issue our request */
+                        __get_cpu_var(mpcpvs_vspin) = t;
+                        break;
+                } else {
+                        /* some job is spinning => enqueue in request queue */
+                        prio_wait_queue_t wait;
+                        wait_queue_head_t* vspin = &__get_cpu_var(mpcpvs_vspin_wait);
+                        unsigned long flags;
 
-                spin_lock_irqsave(&vspin->lock, flags);
+                        /* ordered by regular priority */
+                        init_prio_waitqueue_entry(&wait, t, prio_point(get_priority(t)));
 
-                set_task_state(t, TASK_UNINTERRUPTIBLE);
+                        spin_lock_irqsave(&vspin->lock, flags);
 
-                __add_wait_queue_prio_exclusive(vspin, &wait);
+                        set_task_state(t, TASK_UNINTERRUPTIBLE);
 
-                TS_LOCK_SUSPEND;
+                        __add_wait_queue_prio_exclusive(vspin, &wait);
 
-                spin_unlock_irqrestore(&vspin->lock, flags);
+                        spin_unlock_irqrestore(&vspin->lock, flags);
 
-                preempt_enable_no_resched();
+                        TS_LOCK_SUSPEND;
 
-                schedule();
+                        preempt_enable_no_resched();
 
-                preempt_disable();
+                        schedule();
 
-                TS_LOCK_RESUME;
+                        preempt_disable();
 
-                /* ok, now it is ours */
-                BUG_ON(__get_cpu_var(mpcpvs_vspin) != t);
+                        TS_LOCK_RESUME;
+                        /* Recheck if we got it --- some higher-priority process might
+                         * have swooped in. */
+                }
         }
+        /* ok, now it is ours */
 }
 
 /* called with preemptions off */
@@ -734,20 +737,15 @@ static void mpcp_vspin_exit(void)
 
         BUG_ON(__get_cpu_var(mpcpvs_vspin) != t);
 
+        /* no spinning job */
+        __get_cpu_var(mpcpvs_vspin) = NULL;
+
         /* see if anyone is waiting for us to stop "spinning" */
         spin_lock_irqsave(&vspin->lock, flags);
         next = __waitqueue_remove_first(vspin);
 
-        if (next) {
-                /* grant ownership */
-                __get_cpu_var(mpcpvs_vspin) = next;
-
-                /* let it continue its request */
+        if (next)
                 wake_up_process(next);
-        } else {
-                /* no spinning job */
-                __get_cpu_var(mpcpvs_vspin) = NULL;
-        }
 
         spin_unlock_irqrestore(&vspin->lock, flags);
 }
@@ -769,14 +767,14 @@ int pfp_mpcp_lock(struct litmus_lock* l)
 
         preempt_disable();
 
+        if (sem->vspin)
+                mpcp_vspin_enter();
+
         /* Priority-boost ourself *before* we suspend so that
          * our priority is boosted when we resume. Use the priority
          * ceiling for the local partition. */
         boost_priority(t, sem->prio_ceiling[get_partition(t)]);
 
-        if (sem->vspin)
-                mpcp_vspin_enter();
-
         spin_lock_irqsave(&sem->wait.lock, flags);
 
         preempt_enable_no_resched();