From a25f3ac67f9c467cf945b45fbc0f4e587e640cab Mon Sep 17 00:00:00 2001
From: Steve Reinhardt <stever@eecs.umich.edu>
Date: Tue, 17 Jul 2007 06:33:28 -0700
Subject: Forward cache-to-cache responses through other caches.

--HG--
extra : convert_revision : 5b6a02255bccd98b00949703cf4ba4b221553cea
---
 src/mem/cache/cache_impl.hh | 56 +++++++++++++++++++++++++++++++++++++++------
 1 file changed, 49 insertions(+), 7 deletions(-)

(limited to 'src/mem/cache/cache_impl.hh')

diff --git a/src/mem/cache/cache_impl.hh b/src/mem/cache/cache_impl.hh
index 59571dd6f..c069d8ba9 100644
--- a/src/mem/cache/cache_impl.hh
+++ b/src/mem/cache/cache_impl.hh
@@ -315,6 +315,29 @@ Cache<TagStore>::access(PacketPtr pkt, BlkType *&blk, int &lat)
 }
 
 
+class ForwardResponseRecord : public Packet::SenderState
+{
+    Packet::SenderState *prevSenderState;
+    int prevSrc;
+#ifndef NDEBUG
+    BaseCache *cache;
+#endif
+  public:
+    ForwardResponseRecord(Packet *pkt, BaseCache *_cache)
+        : prevSenderState(pkt->senderState), prevSrc(pkt->getSrc())
+#ifndef NDEBUG
+          , cache(_cache)
+#endif
+    {}
+    void restore(Packet *pkt, BaseCache *_cache)
+    {
+        assert(_cache == cache);
+        pkt->senderState = prevSenderState;
+        pkt->setDest(prevSrc);
+    }
+};
+
+
 template<class TagStore>
 bool
 Cache<TagStore>::timingAccess(PacketPtr pkt)
@@ -325,6 +348,19 @@ Cache<TagStore>::timingAccess(PacketPtr pkt)
     // we charge hitLatency for doing just about anything here
     Tick time =  curTick + hitLatency;
 
+    if (pkt->isResponse()) {
+        // must be cache-to-cache response from upper to lower level
+        ForwardResponseRecord *rec =
+            dynamic_cast<ForwardResponseRecord *>(pkt->senderState);
+        assert(rec != NULL);
+        rec->restore(pkt, this);
+        delete rec;
+        memSidePort->respond(pkt, time);
+        return true;
+    }
+
+    assert(pkt->isRequest());
+
     if (pkt->memInhibitAsserted()) {
         DPRINTF(Cache, "mem inhibited on 0x%x: not responding\n",
                 pkt->getAddr());
@@ -392,6 +428,8 @@ Cache<TagStore>::timingAccess(PacketPtr pkt)
         if (needsResponse) {
             pkt->makeTimingResponse();
             cpuSidePort->respond(pkt, curTick+lat);
+        } else {
+            delete pkt;
         }
     } else {
         // miss
@@ -424,12 +462,6 @@ Cache<TagStore>::timingAccess(PacketPtr pkt)
         }
     }
 
-    if (!needsResponse) {
-        // Need to clean up the packet on a writeback miss, but leave
-        // the request for the next level.
-        delete pkt;
-    }
-
     return true;
 }
 
@@ -872,7 +904,14 @@ Cache<TagStore>::doTimingSupplyResponse(PacketPtr req_pkt,
 {
     // timing-mode snoop responses require a new packet, unless we
     // already made a copy...
-    PacketPtr pkt = already_copied ? req_pkt : new Packet(req_pkt);
+    PacketPtr pkt = already_copied ? req_pkt : new Packet(req_pkt, true);
+    if (!req_pkt->isInvalidate()) {
+        // note that we're ignoring the shared flag on req_pkt... it's
+        // basically irrelveant, as we'll always assert shared unless
+        // it's an exclusive request, in which case the shared line
+        // should never be asserted1
+        pkt->assertShared();
+    }
     pkt->allocate();
     pkt->makeTimingResponse();
     pkt->setDataFromBlock(blk_data, blkSize);
@@ -894,11 +933,14 @@ Cache<TagStore>::handleSnoop(PacketPtr pkt, BlkType *blk,
     if (is_timing) {
         Packet *snoopPkt = new Packet(pkt, true);  // clear flags
         snoopPkt->setExpressSnoop();
+        snoopPkt->senderState = new ForwardResponseRecord(pkt, this);
         cpuSidePort->sendTiming(snoopPkt);
         if (snoopPkt->memInhibitAsserted()) {
             // cache-to-cache response from some upper cache
             assert(!alreadySupplied);
             pkt->assertMemInhibit();
+        } else {
+            delete snoopPkt->senderState;
         }
         if (snoopPkt->sharedAsserted()) {
             pkt->assertShared();
-- 
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