mem: Add basic stats to the buses

This patch adds a basic set of stats which are hard to impossible to
implement using only communication monitors, and are needed for
insight such as bus utilization, transactions through the bus etc.

Stats added include throughput and transaction distribution, and also
a two-dimensional vector capturing how many packets and how much data
is exchanged between the masters and slaves connected to the bus.

1 files changed, 59 insertions, 6 deletions

diff --git a/src/mem/noncoherent_bus.cc b/src/mem/noncoherent_bus.cc
index f6c315297..5bf5cfd88 100644
--- a/src/mem/noncoherent_bus.cc
+++ b/src/mem/noncoherent_bus.cc
@@ -99,11 +99,11 @@ NoncoherentBus::recvTimingReq(PacketPtr pkt, PortID slave_port_id)
     assert(!pkt->isExpressSnoop());
 
     // determine the destination based on the address
-    PortID dest_port_id = findPort(pkt->getAddr());
+    PortID master_port_id = findPort(pkt->getAddr());
 
     // test if the bus should be considered occupied for the current
     // port
-    if (!reqLayer.tryTiming(src_port, dest_port_id)) {
+    if (!reqLayer.tryTiming(src_port, master_port_id)) {
         DPRINTF(NoncoherentBus, "recvTimingReq: src %s %s 0x%x BUSY\n",
                 src_port->name(), pkt->cmdString(), pkt->getAddr());
         return false;
@@ -112,6 +112,11 @@ NoncoherentBus::recvTimingReq(PacketPtr pkt, PortID slave_port_id)
     DPRINTF(NoncoherentBus, "recvTimingReq: src %s %s 0x%x\n",
             src_port->name(), pkt->cmdString(), pkt->getAddr());
 
+    // store size and command as they might be modified when
+    // forwarding the packet
+    unsigned int pkt_size = pkt->hasData() ? pkt->getSize() : 0;
+    unsigned int pkt_cmd = pkt->cmdToIndex();
+
     // set the source port for routing of the response
     pkt->setSrc(slave_port_id);
 
@@ -119,7 +124,7 @@ NoncoherentBus::recvTimingReq(PacketPtr pkt, PortID slave_port_id)
     Tick packetFinishTime = pkt->busLastWordDelay + curTick();
 
     // since it is a normal request, attempt to send the packet
-    bool success = masterPorts[dest_port_id]->sendTimingReq(pkt);
+    bool success = masterPorts[master_port_id]->sendTimingReq(pkt);
 
     if (!success)  {
         // inhibited packets should never be forced to retry
@@ -132,7 +137,7 @@ NoncoherentBus::recvTimingReq(PacketPtr pkt, PortID slave_port_id)
         pkt->busFirstWordDelay = pkt->busLastWordDelay = 0;
 
         // occupy until the header is sent
-        reqLayer.failedTiming(src_port, dest_port_id,
+        reqLayer.failedTiming(src_port, master_port_id,
                               clockEdge(Cycles(headerCycles)));
 
         return false;
@@ -140,6 +145,12 @@ NoncoherentBus::recvTimingReq(PacketPtr pkt, PortID slave_port_id)
 
     reqLayer.succeededTiming(packetFinishTime);
 
+    // stats updates
+    dataThroughBus += pkt_size;
+    pktCount[slave_port_id][master_port_id]++;
+    totPktSize[slave_port_id][master_port_id] += pkt_size;
+    transDist[pkt_cmd]++;
+
     return true;
 }
 
@@ -160,11 +171,18 @@ NoncoherentBus::recvTimingResp(PacketPtr pkt, PortID master_port_id)
     DPRINTF(NoncoherentBus, "recvTimingResp: src %s %s 0x%x\n",
             src_port->name(), pkt->cmdString(), pkt->getAddr());
 
+    // store size and command as they might be modified when
+    // forwarding the packet
+    unsigned int pkt_size = pkt->hasData() ? pkt->getSize() : 0;
+    unsigned int pkt_cmd = pkt->cmdToIndex();
+
     calcPacketTiming(pkt);
     Tick packetFinishTime = pkt->busLastWordDelay + curTick();
 
-    // send the packet to the destination through one of our slave
-    // ports, as determined by the destination field
+    // determine the destination based on what is stored in the packet
+    PortID slave_port_id = pkt->getDest();
+
+    // send the packet through the destination slave port
     bool success M5_VAR_USED = slavePorts[pkt->getDest()]->sendTimingResp(pkt);
 
     // currently it is illegal to block responses... can lead to
@@ -173,6 +191,12 @@ NoncoherentBus::recvTimingResp(PacketPtr pkt, PortID master_port_id)
 
     respLayer.succeededTiming(packetFinishTime);
 
+    // stats updates
+    dataThroughBus += pkt_size;
+    pktCount[slave_port_id][master_port_id]++;
+    totPktSize[slave_port_id][master_port_id] += pkt_size;
+    transDist[pkt_cmd]++;
+
     return true;
 }
 
@@ -192,12 +216,19 @@ NoncoherentBus::recvAtomic(PacketPtr pkt, PortID slave_port_id)
             slavePorts[slave_port_id]->name(), pkt->getAddr(),
             pkt->cmdString());
 
+    // add the request data
+    dataThroughBus += pkt->hasData() ? pkt->getSize() : 0;
+
     // determine the destination port
     PortID dest_id = findPort(pkt->getAddr());
 
     // forward the request to the appropriate destination
     Tick response_latency = masterPorts[dest_id]->sendAtomic(pkt);
 
+    // add the response data
+    if (pkt->isResponse())
+        dataThroughBus += pkt->hasData() ? pkt->getSize() : 0;
+
     // @todo: Not setting first-word time
     pkt->busLastWordDelay = response_latency;
     return response_latency;
@@ -233,3 +264,25 @@ NoncoherentBusParams::create()
 {
     return new NoncoherentBus(this);
 }
+
+void
+NoncoherentBus::regStats()
+{
+    // register the stats of the base class and our two bus layers
+    BaseBus::regStats();
+    reqLayer.regStats();
+    respLayer.regStats();
+
+    dataThroughBus
+        .name(name() + ".data_through_bus")
+        .desc("Total data (bytes)")
+        ;
+
+    throughput
+        .name(name() + ".throughput")
+        .desc("Throughput (bytes/s)")
+        .precision(0)
+        ;
+
+    throughput = dataThroughBus / simSeconds;
+}