mem: Do not allocate space for packet data if not needed

This patch looks at the request and response command to determine if
either actually has any data payload, and if not, we do not allocate
any space for packet data.

The only tricky case is where the command type is changed as part of
the MSHR functionality. In these cases where the original packet had
no data, but the new packet does, we need to explicitly call
allocate().

1 files changed, 12 insertions, 3 deletions

diff --git a/src/mem/packet.hh b/src/mem/packet.hh
index 4614799bf..94508f697 100644
--- a/src/mem/packet.hh
+++ b/src/mem/packet.hh
@@ -508,6 +508,11 @@ class Packet : public Printable
     bool isEviction() const          { return cmd.isEviction(); }
     bool isWriteback() const         { return cmd.isWriteback(); }
     bool hasData() const             { return cmd.hasData(); }
+    bool hasRespData() const
+    {
+        MemCmd resp_cmd = cmd.responseCommand();
+        return resp_cmd.hasData();
+    }
     bool isLLSC() const              { return cmd.isLLSC(); }
     bool isError() const             { return cmd.isError(); }
     bool isPrint() const             { return cmd.isPrint(); }
@@ -1058,9 +1063,13 @@ class Packet : public Printable
     void
     allocate()
     {
-        assert(flags.noneSet(STATIC_DATA|DYNAMIC_DATA));
-        flags.set(DYNAMIC_DATA);
-        data = new uint8_t[getSize()];
+        // if either this command or the response command has a data
+        // payload, actually allocate space
+        if (hasData() || hasRespData()) {
+            assert(flags.noneSet(STATIC_DATA|DYNAMIC_DATA));
+            flags.set(DYNAMIC_DATA);
+            data = new uint8_t[getSize()];
+        }
     }
 
     /** @} */