From f84ee031ccdb63d016c6f55b578085a2e5af4a4b Mon Sep 17 00:00:00 2001
From: Andreas Hansson <andreas.hansson@arm.com>
Date: Wed, 10 Feb 2016 04:08:24 -0500
Subject: [PATCH] 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.
---
 src/mem/cache/cache.cc | 36 +++++++++++-------------------------
 1 file changed, 11 insertions(+), 25 deletions(-)

diff --git a/src/mem/cache/cache.cc b/src/mem/cache/cache.cc
index 7a5d22ef0..189fd4cab 100644
--- 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();