1 files changed, 49 insertions, 8 deletions

diff --git a/litmus/sched_mc.c b/litmus/sched_mc.c
index f3ace9fe560a..43b0731ab38a 100644
--- a/litmus/sched_mc.c
+++ b/litmus/sched_mc.c
@@ -4,6 +4,49 @@
  * Implementation of the Mixed Criticality scheduling algorithm.
  *
  * (Per Mollison, Erickson, Anderson, Baruah, Scoredos 2010)
+ *
+ * Absolute first: relative time spent doing different parts of release
+ * and scheduling overhead needs to be measured and graphed.
+ *
+ * Domain locks should be more fine-grained. There is no reason to hold the
+ * ready-queue lock when adding a task to the release-queue.
+ *
+ * The levels should be converted to linked-lists so that they are more
+ * adaptable and need not be identical on all processors.
+ *
+ * The interaction between remove_from_all and other concurrent operations
+ * should be re-examined. If a job_completion and a preemption happen
+ * simultaneously, a task could be requeued, removed, then requeued again.
+ *
+ * Level-C tasks should be able to swap CPUs a-la GSN-EDF. They should also
+ * try and swap with the last CPU they were on. This could be complicated for
+ * ghost tasks.
+ *
+ * Locking for timer-merging could be infinitely more fine-grained. A second
+ * hash could select a lock to use based on queue slot. This approach might
+ * also help with add_release in rt_domains.
+ *
+ * It should be possible to reserve a CPU for ftdumping.
+ *
+ * The real_deadline business seems sloppy.
+ *
+ * The amount of data in the header file should be cut down. The use of the
+ * header file in general needs to be re-examined.
+ *
+ * The plugin needs to be modified so that it doesn't freeze when it is
+ * deactivated in a VM.
+ *
+ * The locking in check_for_preempt is not fine-grained enough.
+ *
+ * The size of the structures could be smaller. Debugging info might be
+ * excessive as things currently stand.
+ *
+ * The macro can_requeue has been expanded too much. Anything beyond
+ * scheduled_on is a hack!
+ *
+ * Domain names (rt_domain) are still clumsy.
+ *
+ * Should BE be moved into the kernel? This will require benchmarking.
  */
 
 #include <linux/spinlock.h>
@@ -110,7 +153,7 @@ static int cpu_lower_prio(struct bheap_node *a, struct bheap_node *b)
 }
 
 /*
- * Return true if the domain has a higher priority ready task. The curr
+ * Return true if the domain has a higher priority ready task. The @curr
  * task must belong to the domain.
  */
 static int mc_preempt_needed(struct domain *dom, struct task_struct* curr)
@@ -381,6 +424,7 @@ static void link_task_to_cpu(struct cpu_entry *entry, struct task_struct *task)
                 set_rt_flags(task, RT_F_RUNNING);
         }
         entry->linked = task;
+
         /* Higher criticality crit entries are now usable */
         for (; i < entry_level(entry) + 1; i++) {
                 ce = &entry->crit_entries[i];
@@ -418,8 +462,7 @@ static void preempt(struct domain *dom, struct crit_entry *ce)
                 link_task_to_cpu(entry, task);
                 preempt_if_preemptable(entry->scheduled, entry->cpu);
         } else if (old && old == entry->linked) {
-                /*
-                 * Preempted a running task with a ghost job. Null needs to be
+                /* Preempted a running task with a ghost job. Null needs to be
                  * running.
                  */
                 link_task_to_cpu(entry, NULL);
@@ -444,7 +487,7 @@ static void update_crit_levels(struct cpu_entry *entry)
                 ce = &entry->crit_entries[i];
 
                 global_preempted = ce->linked &&
-                        /* This task is running */
+                        /* This task is running on a cpu */
                         ce->linked->rt_param.scheduled_on == entry->cpu &&
                         /* But it was preempted */
                         ce->linked != entry->linked &&
@@ -970,14 +1013,12 @@ static struct task_struct* mc_schedule(struct task_struct* prev)
                 raw_spin_unlock(&entry->lock);
                 raw_spin_lock(dom->lock);
 
-                /* Peek at task here to avoid lock use */
+                /* Do domain stuff before grabbing CPU locks */
                 dtask = dom->peek_ready(dom);
+                fix_crit_position(ce);
 
                 raw_spin_lock(&entry->lock);
 
-                /* Now that we hold the domain lock...*/
-                fix_crit_position(ce);
-
                 if (!entry->linked && !ce->linked && dtask && can_use(ce)) {
                         dom->take_ready(dom);
                         link_task_to_crit(ce, dtask);