mem: Split WriteInvalidateReq into write and invalidate

WriteInvalidateReq ensures that a whole-line write does not incur the
cost of first doing a read exclusive, only to later overwrite the
data. This patch splits the existing WriteInvalidateReq into a
WriteLineReq, which is done locally, and an InvalidateReq that is sent
out throughout the memory system. The WriteLineReq re-uses the normal
WriteResp.

The change allows us to better express the difference between the
cache that is performing the write, and the ones that are merely
invalidating. As a consequence, we no longer have to rely on the
isTopLevel flag. Moreover, the actual memory in the system does not
see the intitial write, only the writeback. We were marking the
written line as dirty already, so there is really no need to also push
the write all the way to the memory.

The overall flow of the write-invalidate operation remains the same,
i.e. the operation is only carried out once the response for the
invalidate comes back. This patch adds the InvalidateResp for this
very reason.

1 files changed, 3 insertions, 6 deletions

diff --git a/src/mem/packet.hh b/src/mem/packet.hh
index 49a50125e..54f2176c6 100644
--- a/src/mem/packet.hh
+++ b/src/mem/packet.hh
@@ -92,8 +92,7 @@ class MemCmd
         HardPFReq,
         SoftPFResp,
         HardPFResp,
-        WriteInvalidateReq,
-        WriteInvalidateResp,
+        WriteLineReq,
         UpgradeReq,
         SCUpgradeReq,           // Special "weak" upgrade for StoreCond
         UpgradeResp,
@@ -122,7 +121,8 @@ class MemCmd
         // Fake simulator-only commands
         PrintReq,       // Print state matching address
         FlushReq,      //request for a cache flush
-        InvalidationReq,   // request for address to be invalidated from lsq
+        InvalidateReq,   // request for address to be invalidated
+        InvalidateResp,
         NUM_MEM_CMDS
     };
 
@@ -188,8 +188,6 @@ class MemCmd
     bool needsExclusive() const    { return testCmdAttrib(NeedsExclusive); }
     bool needsResponse() const     { return testCmdAttrib(NeedsResponse); }
     bool isInvalidate() const      { return testCmdAttrib(IsInvalidate); }
-    bool isWriteInvalidate() const { return testCmdAttrib(IsWrite) &&
-                                            testCmdAttrib(IsInvalidate); }
 
     /**
      * Check if this particular packet type carries payload data. Note
@@ -483,7 +481,6 @@ class Packet : public Printable
     bool needsExclusive() const      { return cmd.needsExclusive(); }
     bool needsResponse() const       { return cmd.needsResponse(); }
     bool isInvalidate() const        { return cmd.isInvalidate(); }
-    bool isWriteInvalidate() const   { return cmd.isWriteInvalidate(); }
     bool hasData() const             { return cmd.hasData(); }
     bool isLLSC() const              { return cmd.isLLSC(); }
     bool isError() const             { return cmd.isError(); }