mem-cache: Fix promoting of targets that need writable

There are cases where a request which does not need a writable copy
gets an response upgraded reponse and fills in a writable copy. When
this happens, we promote deferred MSHR targets that were deferred
because they needed a writable copy to service them immediately.

Previously, we would uncoditionally promote deferred targets. Since
the deferred targets might contain a cache invalidation operation, we
have to make sure that any targets following the cache invalidation is
not promoted.

Change-Id: I1f7b28f7d35f84329e065c8f63117db21852365a
Reviewed-on: https://gem5-review.googlesource.com/11016
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/src/mem/cache/mshr.hh b/src/mem/cache/mshr.hh
index f93d3c0f5..71c2da2c4 100644
--- a/src/mem/cache/mshr.hh
+++ b/src/mem/cache/mshr.hh
@@ -385,6 +385,13 @@ class MSHR : public QueueEntry, public Printable
 
     bool promoteDeferredTargets();
 
+    /**
+     * Promotes deferred targets that do not require writable
+     *
+     * Requests in the deferred target list are moved to the target
+     * list up until the first target that is a cache maintenance
+     * operation or needs a writable copy of the block
+     */
     void promoteWritable();
 
     bool checkFunctional(PacketPtr pkt);