mem-cache: Determine if an MSHR has requests from another cache

To decide whether we allocate upon receiving a response we need to
determine if any of the currently serviced requests (non-deferred
targets) is comming from another cache. This change adds support for
tracking this information in the MSHR.

Change-Id: If1db93c12b6af5813b91b9d6b6e5e196d327f038
Reviewed-on: https://gem5-review.googlesource.com/10422
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>

1 files changed, 23 insertions, 2 deletions

diff --git a/src/mem/cache/mshr.hh b/src/mem/cache/mshr.hh
index 5fe0fb92d..b4bf33a4f 100644
--- a/src/mem/cache/mshr.hh
+++ b/src/mem/cache/mshr.hh
@@ -162,6 +162,11 @@ class MSHR : public QueueEntry, public Printable
         bool hasUpgrade;
         /** Set when the response should allocate on fill */
         bool allocOnFill;
+        /**
+         * Determine whether there was at least one non-snooping
+         * target coming from another cache.
+         */
+        bool hasFromCache;
 
         TargetList();
 
@@ -176,7 +181,12 @@ class MSHR : public QueueEntry, public Printable
         void updateFlags(PacketPtr pkt, Target::Source source,
                          bool alloc_on_fill);
 
-        void resetFlags() { needsWritable = hasUpgrade = allocOnFill = false; }
+        void resetFlags() {
+            needsWritable = false;
+            hasUpgrade = false;
+            allocOnFill = false;
+            hasFromCache = false;
+        }
 
         /**
          * Goes through the list of targets and uses them to populate
@@ -191,7 +201,8 @@ class MSHR : public QueueEntry, public Printable
          * values.
          */
         bool isReset() const {
-            return !needsWritable && !hasUpgrade && !allocOnFill;
+            return !needsWritable && !hasUpgrade && !allocOnFill &&
+                !hasFromCache;
         }
 
         /**
@@ -257,6 +268,16 @@ class MSHR : public QueueEntry, public Printable
     bool allocOnFill() const {
         return targets.allocOnFill;
     }
+
+    /**
+     * Determine if there are non-deferred requests from other caches
+     *
+     * @return true if any of the targets is from another cache
+     */
+    bool hasFromCache() const {
+        return targets.hasFromCache;
+    }
+
   private:
 
     /**