mem: Align cache behaviour in atomic when upstream is responding

Adopt the same flow as in timing mode, where the caches on the path to
memory get to keep the line (if present), and we use the
responderHadWritable flag to determine if we need to forward the
(invalidating) packet or not.

diff --git a/src/mem/cache/cache.cc b/src/mem/cache/cache.cc
index 7a5d22ef052465b55c05fe2edb7ef28f4921e1a2..189fd4cab181cc68dc28872a25e40a9ca6bd451c 100644 (file)
--- a/src/mem/cache/cache.cc
+++ b/src/mem/cache/cache.cc
@@ -1011,8 +1011,6 @@ Cache::recvAtomic(PacketPtr pkt)
 {
     // We are in atomic mode so we pay just for lookupLatency here.
     Cycles lat = lookupLatency;
-    // @TODO: make this a parameter
-    bool last_level_cache = false;
 
     // Forward the request if the system is in cache bypass mode.
     if (system->bypassCaches())
@@ -1020,30 +1018,18 @@ Cache::recvAtomic(PacketPtr pkt)
 
     promoteWholeLineWrites(pkt);
 
+    // follow the same flow as in recvTimingReq, and check if a cache
+    // above us is responding
     if (pkt->cacheResponding()) {
-        // have to invalidate ourselves and any lower caches even if
-        // upper cache will be responding
-        if (pkt->isInvalidate()) {
-            CacheBlk *blk = tags->findBlock(pkt->getAddr(), pkt->isSecure());
-            if (blk && blk->isValid()) {
-                tags->invalidate(blk);
-                blk->invalidate();
-                DPRINTF(Cache, "Other cache responding to %s on %#llx (%s):"
-                        " invalidating\n",
-                        pkt->cmdString(), pkt->getAddr(),
-                        pkt->isSecure() ? "s" : "ns");
-            }
-            if (!last_level_cache) {
-                DPRINTF(Cache, "Other cache responding to %s on %#llx (%s):"
-                        " forwarding\n",
-                        pkt->cmdString(), pkt->getAddr(),
-                        pkt->isSecure() ? "s" : "ns");
-                lat += ticksToCycles(memSidePort->sendAtomic(pkt));
-            }
-        } else {
-            DPRINTF(Cache, "Other cache responding to %s on %#llx: "
-                    "not responding\n",
-                    pkt->cmdString(), pkt->getAddr());
+        DPRINTF(Cache, "Cache above responding to %#llx (%s): "
+                "not responding\n",
+                pkt->getAddr(), pkt->isSecure() ? "s" : "ns");
+
+        // if a cache is responding, and it had the line in Owned
+        // rather than Modified state, we need to invalidate any
+        // copies that are not on the same path to memory
+        if (pkt->needsWritable() && !pkt->responderHadWritable()) {
+            lat += ticksToCycles(memSidePort->sendAtomic(pkt));
         }
 
         return lat * clockPeriod();