mem-cache: Align how we handle requests in atomic with timing

Requests, for which a cache has already committed to respond do not
perform any lookups. Previously in atomic mode the packet would pay
the lookup latency while in timing it wouldn't. This patch aligns
recvAtomic with recvTimingReq and removes the lookup latency from the
the handling of such requests.

Change-Id: I50a0631f8058e5086d94d55af0e1788a60e2883f
Signed-off-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/14175
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

src/mem/cache/base.cc

@@ -569,29 +569,14 @@ BaseCache::recvTimingResp(PacketPtr pkt)
 Tick
 BaseCache::recvAtomic(PacketPtr pkt)
 {
-    // We are in atomic mode so we pay just for lookupLatency here.
-    Cycles lat = lookupLatency;
-
-    // follow the same flow as in recvTimingReq, and check if a cache
-    // above us is responding
-    if (pkt->cacheResponding() && !pkt->isClean()) {
-        assert(!pkt->req->isCacheInvalidate());
-        DPRINTF(Cache, "Cache above responding to %s: not responding\n",
-                pkt->print());
-
-        // 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
-        assert(pkt->needsWritable() && !pkt->responderHadWritable());
-        lat += ticksToCycles(memSidePort.sendAtomic(pkt));
-
-        return lat * clockPeriod();
-    }
-
     // should assert here that there are no outstanding MSHRs or
     // writebacks... that would mean that someone used an atomic
     // access in timing mode
 
+    // We use lookupLatency here because it is used to specify the latency
+    // to access.
+    Cycles lat = lookupLatency;
+
     CacheBlk *blk = nullptr;
     PacketList writebacks;
     bool satisfied = access(pkt, blk, lat, writebacks);

src/mem/cache/cache.cc

@@ -658,6 +658,21 @@ 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()) {
+        assert(!pkt->req->isCacheInvalidate());
+        DPRINTF(Cache, "Cache above responding to %s: not responding\n",
+                pkt->print());
+
+        // 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
+        assert(pkt->needsWritable() && !pkt->responderHadWritable());
+
+        return memSidePort.sendAtomic(pkt);
+    }
+
     return BaseCache::recvAtomic(pkt);
 }