sim: ScopedMigration does nothing if both eqs are the same

Added a check to avoid unlocking/locking the same event queue. Also,
added an optional parameter to enable the migration to be skipped. This
can be useful to disable the synchronization for certain runtime
conditions.

Change-Id: I4b03b3ffff4f9503153cd41dd8aa78705bf16cc4
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/5730
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>

1 files changed, 16 insertions, 8 deletions

diff --git a/src/sim/eventq.hh b/src/sim/eventq.hh
index 6d68b4e3a..0a0405fef 100644
--- a/src/sim/eventq.hh
+++ b/src/sim/eventq.hh
@@ -542,28 +542,36 @@ class EventQueue
      * example, be useful when performing IO across thread event
      * queues when timing is not crucial (e.g., during fast
      * forwarding).
+     *
+     * ScopedMigration does nothing if both eqs are the same
      */
     class ScopedMigration
     {
       public:
-        ScopedMigration(EventQueue *_new_eq)
-            :  new_eq(*_new_eq), old_eq(*curEventQueue())
+        ScopedMigration(EventQueue *_new_eq, bool _doMigrate = true)
+            :new_eq(*_new_eq), old_eq(*curEventQueue()),
+             doMigrate((&new_eq != &old_eq)&&_doMigrate)
         {
-            old_eq.unlock();
-            new_eq.lock();
-            curEventQueue(&new_eq);
+            if (doMigrate){
+                old_eq.unlock();
+                new_eq.lock();
+                curEventQueue(&new_eq);
+            }
         }
 
         ~ScopedMigration()
         {
-            new_eq.unlock();
-            old_eq.lock();
-            curEventQueue(&old_eq);
+            if (doMigrate){
+                new_eq.unlock();
+                old_eq.lock();
+                curEventQueue(&old_eq);
+            }
         }
 
       private:
         EventQueue &new_eq;
         EventQueue &old_eq;
+        bool doMigrate;
     };
 
     /**