the bridge never returns false when recvTiming() is called on its ports now, it always returns true and nacks the packet if there isn't sufficient buffer space

fix the timing cpu to handle receiving a nacked packet

src/cpu/simple/timing.cc:
    make the timing cpu handle receiving a nacked packet
src/mem/bridge.cc:
src/mem/bridge.hh:
    the bridge never returns false when recvTiming() is called on its ports now, it always returns true and nacks the packet if there isn't sufficient buffer space

--HG--
extra : convert_revision : 5e12d0cf6ce985a5f72bcb7ce26c83a76c34c50a

2 files changed, 81 insertions, 28 deletions

diff --git a/src/mem/bridge.cc b/src/mem/bridge.cc
index b25d135e2..e7d52b178 100644
--- a/src/mem/bridge.cc
+++ b/src/mem/bridge.cc
@@ -47,7 +47,8 @@ Bridge::BridgePort::BridgePort(const std::string &_name,
                                bool fix_partial_write)
     : Port(_name), bridge(_bridge), otherPort(_otherPort),
       delay(_delay), fixPartialWrite(fix_partial_write),
-      outstandingResponses(0), queueLimit(_queueLimit), sendEvent(this)
+      outstandingResponses(0), queuedRequests(0),
+      queueLimit(_queueLimit), sendEvent(this)
 {
 }
 
@@ -92,34 +93,70 @@ Bridge::init()
         fatal("Busses don't have the same block size... Not supported.\n");
 }
 
+bool
+Bridge::BridgePort::queueFull()
+{
+    // use >= here because sendQueue could get larger because of
+    // nacks getting inserted
+    return queuedRequests + outstandingResponses >= queueLimit;
+}
 
 /** Function called by the port when the bus is receiving a Timing
  * transaction.*/
 bool
 Bridge::BridgePort::recvTiming(PacketPtr pkt)
 {
-    if (pkt->flags & SNOOP_COMMIT) {
-        DPRINTF(BusBridge, "recvTiming: src %d dest %d addr 0x%x\n",
+    if (!(pkt->flags & SNOOP_COMMIT))
+        return true;
+
+
+    DPRINTF(BusBridge, "recvTiming: src %d dest %d addr 0x%x\n",
                 pkt->getSrc(), pkt->getDest(), pkt->getAddr());
 
-        return otherPort->queueForSendTiming(pkt);
+    if (pkt->isRequest() && otherPort->queueFull()) {
+        DPRINTF(BusBridge, "Remote queue full, nacking\n");
+        nackRequest(pkt);
+        return true;
     }
-    else {
-        // Else it's just a snoop, properly return if we are blocking
-        return !queueFull();
+
+    if (pkt->needsResponse() && pkt->result != Packet::Nacked)
+        if (queueFull()) {
+            DPRINTF(BusBridge, "Local queue full, no space for response, nacking\n");
+            DPRINTF(BusBridge, "queue size: %d outreq: %d outstanding resp: %d\n",
+                    sendQueue.size(), queuedRequests, outstandingResponses);
+            nackRequest(pkt);
+            return true;
+        } else {
+            DPRINTF(BusBridge, "Request Needs response, reserving space\n");
+            ++outstandingResponses;
+        }
+
+    otherPort->queueForSendTiming(pkt);
+
+    return true;
+}
+
+void
+Bridge::BridgePort::nackRequest(PacketPtr pkt)
+{
+    // Nack the packet
+    pkt->result = Packet::Nacked;
+    pkt->setDest(pkt->getSrc());
+
+    //put it on the list to send
+    Tick readyTime = curTick + delay;
+    PacketBuffer *buf = new PacketBuffer(pkt, readyTime, true);
+    if (sendQueue.empty()) {
+        sendEvent.schedule(readyTime);
     }
+    sendQueue.push_back(buf);
 }
 
 
-bool
+void
 Bridge::BridgePort::queueForSendTiming(PacketPtr pkt)
 {
-    if (queueFull()) {
-        DPRINTF(BusBridge, "Queue full, returning false\n");
-        return false;
-    }
-
-   if (pkt->isResponse()) {
+   if (pkt->isResponse() || pkt->result == Packet::Nacked) {
         // This is a response for a request we forwarded earlier.  The
         // corresponding PacketBuffer should be stored in the packet's
         // senderState field.
@@ -128,6 +165,13 @@ Bridge::BridgePort::queueForSendTiming(PacketPtr pkt)
         // set up new packet dest & senderState based on values saved
         // from original request
         buf->fixResponse(pkt);
+
+        // Check if this packet was expecting a response (this is either it or
+        // its a nacked packet and we won't be seeing that response)
+        if (buf->expectResponse)
+            --outstandingResponses;
+
+
         DPRINTF(BusBridge, "restoring  sender state: %#X, from packet buffer: %#X\n",
                         pkt->senderState, buf);
         DPRINTF(BusBridge, "  is response, new dest %d\n", pkt->getDest());
@@ -146,10 +190,8 @@ Bridge::BridgePort::queueForSendTiming(PacketPtr pkt)
     if (sendQueue.empty()) {
         sendEvent.schedule(readyTime);
     }
-
+    ++queuedRequests;
     sendQueue.push_back(buf);
-
-    return true;
 }
 
 void
@@ -169,7 +211,8 @@ Bridge::BridgePort::trySend()
     pkt->flags &= ~SNOOP_COMMIT; //CLear it if it was set
 
     if (pkt->cmd == MemCmd::WriteInvalidateReq && fixPartialWrite &&
-            pkt->getOffset(pbs) && pkt->getSize() != pbs) {
+            pkt->result != Packet::Nacked && pkt->getOffset(pbs) &&
+            pkt->getSize() != pbs) {
         buf->partialWriteFix(this);
         pkt = buf->pkt;
     }
@@ -184,10 +227,7 @@ Bridge::BridgePort::trySend()
         buf->pkt = NULL; // we no longer own packet, so it's not safe to look at it
 
         if (buf->expectResponse) {
-            // Must wait for response.  We just need to count outstanding
-            // responses (in case we want to cap them); PacketBuffer
-            // pointer will be recovered on response.
-            ++outstandingResponses;
+            // Must wait for response
             DPRINTF(BusBridge, "  successful: awaiting response (%d)\n",
                     outstandingResponses);
         } else {
@@ -196,13 +236,17 @@ Bridge::BridgePort::trySend()
             delete buf;
         }
 
+        if (!buf->nacked)
+                --queuedRequests;
+
         // If there are more packets to send, schedule event to try again.
         if (!sendQueue.empty()) {
             buf = sendQueue.front();
+            DPRINTF(BusBridge, "Scheduling next send\n");
             sendEvent.schedule(std::max(buf->ready, curTick + 1));
         }
         // Let things start sending again
-        if (was_full) {
+        if (was_full && !queueFull()) {
           DPRINTF(BusBridge, "Queue was full, sending retry\n");
           otherPort->sendRetry();
         }
@@ -211,6 +255,8 @@ Bridge::BridgePort::trySend()
         DPRINTF(BusBridge, "  unsuccessful\n");
         buf->undoPartialWriteFix();
     }
+    DPRINTF(BusBridge, "trySend: queue size: %d outreq: %d outstanding resp: %d\n",
+                    sendQueue.size(), queuedRequests, outstandingResponses);
 }
 
 
@@ -290,3 +336,4 @@ CREATE_SIM_OBJECT(Bridge)
 }
 
 REGISTER_SIM_OBJECT("Bridge", Bridge)
+
diff --git a/src/mem/bridge.hh b/src/mem/bridge.hh
index d1154eda0..1fa9cdffc 100644
--- a/src/mem/bridge.hh
+++ b/src/mem/bridge.hh
@@ -79,13 +79,16 @@ class Bridge : public MemObject
 
             bool partialWriteFixed;
             PacketPtr oldPkt;
+            bool nacked;
 
-            PacketBuffer(PacketPtr _pkt, Tick t)
+            PacketBuffer(PacketPtr _pkt, Tick t, bool nack = false)
                 : ready(t), pkt(_pkt),
                   origSenderState(_pkt->senderState), origSrc(_pkt->getSrc()),
-                  expectResponse(_pkt->needsResponse()), partialWriteFixed(false)
+                  expectResponse(_pkt->needsResponse() && !nack),
+                  partialWriteFixed(false), nacked(nack)
+
             {
-                if (!pkt->isResponse())
+                if (!pkt->isResponse() && !nack)
                     pkt->senderState = this;
             }
 
@@ -144,6 +147,7 @@ class Bridge : public MemObject
         std::list<PacketBuffer*> sendQueue;
 
         int outstandingResponses;
+        int queuedRequests;
 
         /** Max queue size for outbound packets */
         int queueLimit;
@@ -151,12 +155,14 @@ class Bridge : public MemObject
         /**
          * Is this side blocked from accepting outbound packets?
          */
-        bool queueFull() { return (sendQueue.size() == queueLimit); }
+        bool queueFull();
 
-        bool queueForSendTiming(PacketPtr pkt);
+        void queueForSendTiming(PacketPtr pkt);
 
         void finishSend(PacketBuffer *buf);
 
+        void nackRequest(PacketPtr pkt);
+
         /**
          * Handle send event, scheduled when the packet at the head of
          * the outbound queue is ready to transmit (for timing