mem: Add snoops for CleanEvicts and Writebacks in atomic mode

This patch mirrors the logic in timing mode which sends up snoops to
check for cached copies before sending CleanEvicts and Writebacks down
the memory hierarchy. In case there is a copy in a cache above,
discard CleanEvicts and set the BLOCK_CACHED flag in Writebacks so
that writebacks do not reset the cache residency bit in the snoop
filter below.

1 files changed, 18 insertions, 2 deletions

diff --git a/src/mem/coherent_xbar.cc b/src/mem/coherent_xbar.cc
index b07356ede..7181cb965 100644
--- a/src/mem/coherent_xbar.cc
+++ b/src/mem/coherent_xbar.cc
@@ -605,6 +605,13 @@ CoherentXBar::recvAtomic(PacketPtr pkt, PortID slave_port_id)
                     " SF size: %i lat: %i\n", __func__,
                     slavePorts[slave_port_id]->name(), pkt->cmdString(),
                     pkt->getAddr(), sf_res.first.size(), sf_res.second);
+
+            // let the snoop filter know about the success of the send
+            // operation, and do it even before sending it onwards to
+            // avoid situations where atomic upward snoops sneak in
+            // between and change the filter state
+            snoopFilter->updateRequest(pkt, *slavePorts[slave_port_id], false);
+
             snoop_result = forwardAtomic(pkt, slave_port_id, InvalidPortID,
                                          sf_res.first);
         } else {
@@ -614,6 +621,15 @@ CoherentXBar::recvAtomic(PacketPtr pkt, PortID slave_port_id)
         snoop_response_latency += snoop_result.second;
     }
 
+    // forwardAtomic snooped into peer caches of the sender, and if
+    // this is a clean evict, but the packet is found in a cache, do
+    // not forward it
+    if (pkt->cmd == MemCmd::CleanEvict && pkt->isBlockCached()) {
+        DPRINTF(CoherentXBar, "recvAtomic: Clean evict 0x%x still cached, "
+                "not forwarding\n", pkt->getAddr());
+        return 0;
+    }
+
     // even if we had a snoop response, we must continue and also
     // perform the actual request at the destination
     PortID master_port_id = findPort(pkt->getAddr());
@@ -626,8 +642,8 @@ CoherentXBar::recvAtomic(PacketPtr pkt, PortID slave_port_id)
     // forward the request to the appropriate destination
     Tick response_latency = masterPorts[master_port_id]->sendAtomic(pkt);
 
-    // Lower levels have replied, tell the snoop filter
-    if (snoopFilter && !system->bypassCaches() && pkt->isResponse()) {
+    // if lower levels have replied, tell the snoop filter
+    if (!system->bypassCaches() && snoopFilter && pkt->isResponse()) {
         snoopFilter->updateResponse(pkt, *slavePorts[slave_port_id]);
     }