P-FP: avoid cross-migrations

The first attempt at DPCP migrations caused deadlocks
if to processors needed to exchange jobs. We avoid this
now by first performing the context switch before enqueuing
the job in the remote runqueue.

1 files changed, 30 insertions, 10 deletions

diff --git a/litmus/sched_pfp.c b/litmus/sched_pfp.c
index a86f7df04f85..4b14a3eedb83 100644
--- a/litmus/sched_pfp.c
+++ b/litmus/sched_pfp.c
@@ -237,6 +237,34 @@ static struct task_struct* pfp_schedule(struct task_struct * prev)
         return next;
 }
 
+#ifdef CONFIG_LITMUS_LOCKING
+
+/* prev is no longer scheduled --- see if it needs to migrate */
+static void pfp_finish_switch(struct task_struct *prev)
+{
+        pfp_domain_t *to;
+
+        if (is_realtime(prev) &&
+            is_running(prev) &&
+            get_partition(prev) != smp_processor_id()) {
+                TRACE_TASK(prev, "needs to migrate from P%d to P%d\n",
+                           smp_processor_id(), get_partition(prev));
+
+                to = task_pfp(prev);
+
+                raw_spin_lock(&to->slock);
+
+                TRACE_TASK(prev, "adding to queue on P%d\n", to->cpu);
+                requeue(prev, to);
+                if (fp_preemption_needed(&to->ready_queue, to->scheduled))
+                        preempt(to);
+
+                raw_spin_unlock(&to->slock);
+
+        }
+}
+
+#endif
 
 /*      Prepare a task for running in RT mode
  */
@@ -1172,7 +1200,7 @@ static inline struct dpcp_semaphore* dpcp_from_lock(struct litmus_lock* lock)
 static void pfp_migrate_to(int target_cpu)
 {
         struct task_struct* t = current;
-        pfp_domain_t *from, *to;
+        pfp_domain_t *from;
 
         if (get_partition(t) == target_cpu)
                 return;
@@ -1187,7 +1215,6 @@ static void pfp_migrate_to(int target_cpu)
 
         /* lock both pfp domains in order of address */
         from = task_pfp(t);
-        to   = remote_pfp(target_cpu);
 
         raw_spin_lock(&from->slock);
 
@@ -1196,14 +1223,6 @@ static void pfp_migrate_to(int target_cpu)
 
         raw_spin_unlock(&from->slock);
 
-        raw_spin_lock(&to->slock);
-
-        requeue(t, to);
-        if (fp_preemption_needed(&to->ready_queue, to->scheduled))
-                preempt(to);
-
-        raw_spin_unlock(&to->slock);
-
         local_irq_enable();
         preempt_enable_no_resched();
 
@@ -1472,6 +1491,7 @@ static struct sched_plugin pfp_plugin __cacheline_aligned_in_smp = {
         .activate_plugin        = pfp_activate_plugin,
 #ifdef CONFIG_LITMUS_LOCKING
         .allocate_lock          = pfp_allocate_lock,
+        .finish_switch          = pfp_finish_switch,
 #endif
 };