MEM: Add the communication monitor

This patch adds a communication monitor MemObject that can be inserted
between a master and slave port to provide a range of statistics about
the communication passing through it. The communication monitor is
non-invasive and does not change any properties or timing of the
packets, with the exception of adding a sender state to be able to
track latency. The statistics are only collected in timing mode (not
atomic) to avoid slowing down any fast forwarding.

An example of the statistics captured by the monitor are: read/write
burst lengths, bandwidth, request-response latency, outstanding
transactions, inter transaction time, transaction count, and address
distribution. The monitor can be used in combination with periodic
resetting and dumping of stats (through schedStatEvent) to study the
behaviour over time.

In future patches, a selection of convenience scripts will be added to
aid in visualising the statistics collected by the monitor.

1 files changed, 538 insertions, 0 deletions

diff --git a/src/mem/comm_monitor.cc b/src/mem/comm_monitor.cc
new file mode 100644
index 000000000..4255d58ad
--- /dev/null
+++ b/src/mem/comm_monitor.cc
@@ -0,0 +1,538 @@
+/*
+ * Copyright (c) 2012 ARM Limited
+ * All rights reserved
+ *
+ * The license below extends only to copyright in the software and shall
+ * not be construed as granting a license to any other intellectual
+ * property including but not limited to intellectual property relating
+ * to a hardware implementation of the functionality of the software
+ * licensed hereunder.  You may use the software subject to the license
+ * terms below provided that you ensure that this notice is replicated
+ * unmodified and in its entirety in all distributions of the software,
+ * modified or unmodified, in source code or in binary form.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Thomas Grass
+ *          Andreas Hansson
+ */
+
+#include "debug/CommMonitor.hh"
+#include "mem/comm_monitor.hh"
+#include "sim/stats.hh"
+
+CommMonitor::CommMonitor(Params* params)
+    : MemObject(params),
+      masterPort(name() + "-master", *this),
+      slavePort(name() + "-slave", *this),
+      samplePeriodicEvent(this),
+      samplePeriodTicks(params->sample_period),
+      readAddrMask(params->read_addr_mask),
+      writeAddrMask(params->write_addr_mask),
+      stats(params)
+{
+    // keep track of the sample period both in ticks and absolute time
+    samplePeriod.setTick(params->sample_period);
+
+    DPRINTF(CommMonitor,
+            "Created monitor %s with sample period %d ticks (%f s)\n",
+            name(), samplePeriodTicks, samplePeriod);
+}
+
+CommMonitor*
+CommMonitorParams::create()
+{
+    return new CommMonitor(this);
+}
+
+void
+CommMonitor::init()
+{
+    // make sure both sides of the monitor are connected
+    if (!slavePort.isConnected() || !masterPort.isConnected())
+        fatal("Communication monitor is not connected on both sides.\n");
+}
+
+MasterPort&
+CommMonitor::getMasterPort(const std::string& if_name, int idx)
+{
+    if (if_name == "master") {
+        return masterPort;
+    } else {
+        return MemObject::getMasterPort(if_name, idx);
+    }
+}
+
+SlavePort&
+CommMonitor::getSlavePort(const std::string& if_name, int idx)
+{
+    if (if_name == "slave") {
+        return slavePort;
+    } else {
+        return MemObject::getSlavePort(if_name, idx);
+    }
+}
+
+void
+CommMonitor::recvFunctional(PacketPtr pkt)
+{
+    masterPort.sendFunctional(pkt);
+}
+
+void
+CommMonitor::recvFunctionalSnoop(PacketPtr pkt)
+{
+    slavePort.sendFunctionalSnoop(pkt);
+}
+
+Tick
+CommMonitor::recvAtomic(PacketPtr pkt)
+{
+    return masterPort.sendAtomic(pkt);
+}
+
+Tick
+CommMonitor::recvAtomicSnoop(PacketPtr pkt)
+{
+    return slavePort.sendAtomicSnoop(pkt);
+}
+
+bool
+CommMonitor::recvTimingReq(PacketPtr pkt)
+{
+    // should always see a request
+    assert(pkt->isRequest());
+
+    // Store relevant fields of packet, because packet may be modified
+    // or even deleted when sendTiming() is called.
+    bool isRead = pkt->isRead();
+    bool isWrite = pkt->isWrite();
+    unsigned size = pkt->getSize();
+    Addr addr = pkt->getAddr();
+    bool needsResponse = pkt->needsResponse();
+    bool memInhibitAsserted = pkt->memInhibitAsserted();
+    Packet::SenderState* senderState = pkt->senderState;
+
+    // If a cache miss is served by a cache, a monitor near the memory
+    // would see a request which needs a response, but this response
+    // would be inhibited and not come back from the memory. Therefore
+    // we additionally have to check the inhibit flag.
+    if (needsResponse && !memInhibitAsserted && !stats.disableLatencyHists) {
+        pkt->senderState = new CommMonitorSenderState(senderState,
+                                                      curTick());
+    }
+
+    // Attempt to send the packet (always succeeds for inhibited
+    // packets)
+    bool successful = masterPort.sendTimingReq(pkt);
+
+    // If not successful, restore the sender state
+    if (!successful && needsResponse && !stats.disableLatencyHists) {
+        delete pkt->senderState;
+        pkt->senderState = senderState;
+    }
+
+    if (successful && isRead) {
+        DPRINTF(CommMonitor, "Forwarded read request\n");
+
+        // Increment number of observed read transactions
+        if (!stats.disableTransactionHists) {
+            ++stats.readTrans;
+        }
+
+        // Get sample of burst length
+        if (!stats.disableBurstLengthHists) {
+            stats.readBurstLengthHist.sample(size);
+        }
+
+        // Sample the masked address
+        if (!stats.disableAddrDists) {
+            stats.readAddrDist.sample(addr & readAddrMask);
+        }
+
+        // If it needs a response increment number of outstanding read
+        // requests
+        if (!stats.disableOutstandingHists && needsResponse) {
+            ++stats.outstandingReadReqs;
+        }
+
+        if (!stats.disableITTDists) {
+            // Sample value of read-read inter transaction time
+            if (stats.timeOfLastRead != 0) {
+                stats.ittReadRead.sample(curTick() - stats.timeOfLastRead);
+            }
+            stats.timeOfLastRead = curTick();
+
+            // Sample value of req-req inter transaction time
+            if (stats.timeOfLastReq != 0) {
+                stats.ittReqReq.sample(curTick() - stats.timeOfLastReq);
+            }
+            stats.timeOfLastReq = curTick();
+        }
+    } else if (successful && isWrite) {
+        DPRINTF(CommMonitor, "Forwarded write request\n");
+
+        // Same as for reads
+        if (!stats.disableTransactionHists) {
+            ++stats.writeTrans;
+        }
+
+        if (!stats.disableBurstLengthHists) {
+            stats.writeBurstLengthHist.sample(size);
+        }
+
+        // Update the bandwidth stats on the request
+        if (!stats.disableBandwidthHists) {
+            stats.writtenBytes += size;
+            stats.totalWrittenBytes += size;
+        }
+
+        // Sample the masked write address
+        if (!stats.disableAddrDists) {
+            stats.writeAddrDist.sample(addr & writeAddrMask);
+        }
+
+        if (!stats.disableOutstandingHists && needsResponse) {
+            ++stats.outstandingWriteReqs;
+        }
+
+        if (!stats.disableITTDists) {
+            // Sample value of write-to-write inter transaction time
+            if (stats.timeOfLastWrite != 0) {
+                stats.ittWriteWrite.sample(curTick() - stats.timeOfLastWrite);
+            }
+            stats.timeOfLastWrite = curTick();
+
+            // Sample value of req-to-req inter transaction time
+            if (stats.timeOfLastReq != 0) {
+                stats.ittReqReq.sample(curTick() - stats.timeOfLastReq);
+            }
+            stats.timeOfLastReq = curTick();
+        }
+    } else if (successful) {
+        DPRINTF(CommMonitor, "Forwarded non read/write request\n");
+    }
+
+    return successful;
+}
+
+bool
+CommMonitor::recvTimingResp(PacketPtr pkt)
+{
+    // should always see responses
+    assert(pkt->isResponse());
+
+    // Store relevant fields of packet, because packet may be modified
+    // or even deleted when sendTiming() is called.
+    bool isRead = pkt->isRead();
+    bool isWrite = pkt->isWrite();
+    unsigned size = pkt->getSize();
+    Tick latency = 0;
+    CommMonitorSenderState* commReceivedState =
+        dynamic_cast<CommMonitorSenderState*>(pkt->senderState);
+
+    if (!stats.disableLatencyHists) {
+        // Restore initial sender state
+        if (commReceivedState == NULL)
+            panic("Monitor got a response without monitor sender state\n");
+
+        // Restore the sate
+        pkt->senderState = commReceivedState->origSenderState;
+    }
+
+    // Attempt to send the packet
+    bool successful = slavePort.sendTimingResp(pkt);
+
+    if (!stats.disableLatencyHists) {
+        // If packet successfully send, sample value of latency,
+        // afterwards delete sender state, otherwise restore state
+        if (successful) {
+            latency = curTick() - commReceivedState->transmitTime;
+            DPRINTF(CommMonitor, "Latency: %d\n", latency);
+            delete commReceivedState;
+        } else {
+            // Don't delete anything and let the packet look like we
+            // did not touch it
+            pkt->senderState = commReceivedState;
+        }
+    }
+
+    if (successful && isRead) {
+        // Decrement number of outstanding read requests
+        DPRINTF(CommMonitor, "Received read response\n");
+        if (!stats.disableOutstandingHists) {
+            assert(stats.outstandingReadReqs != 0);
+            --stats.outstandingReadReqs;
+        }
+
+        if (!stats.disableLatencyHists) {
+            stats.readLatencyHist.sample(latency);
+        }
+
+        // Update the bandwidth stats based on responses for reads
+        if (!stats.disableBandwidthHists) {
+            stats.readBytes += size;
+            stats.totalReadBytes += size;
+        }
+
+    } else if (successful && isWrite) {
+        // Decrement number of outstanding write requests
+        DPRINTF(CommMonitor, "Received write response\n");
+        if (!stats.disableOutstandingHists) {
+            assert(stats.outstandingWriteReqs != 0);
+            --stats.outstandingWriteReqs;
+        }
+
+        if (!stats.disableLatencyHists) {
+            stats.writeLatencyHist.sample(latency);
+        }
+    } else if (successful) {
+        DPRINTF(CommMonitor, "Received non read/write response\n");
+    }
+    return successful;
+}
+
+void
+CommMonitor::recvTimingSnoopReq(PacketPtr pkt)
+{
+    slavePort.sendTimingSnoopReq(pkt);
+}
+
+bool
+CommMonitor::recvTimingSnoopResp(PacketPtr pkt)
+{
+    return masterPort.sendTimingSnoopResp(pkt);
+}
+
+bool
+CommMonitor::isSnooping() const
+{
+    return slavePort.getMasterPort().isSnooping();
+}
+
+unsigned
+CommMonitor::deviceBlockSizeMaster()
+{
+    return slavePort.peerBlockSize();
+}
+
+unsigned
+CommMonitor::deviceBlockSizeSlave()
+{
+    return masterPort.peerBlockSize();
+}
+
+AddrRangeList
+CommMonitor::getAddrRanges()
+{
+    return masterPort.getSlavePort().getAddrRanges();
+}
+
+void
+CommMonitor::recvRetryMaster()
+{
+    slavePort.sendRetry();
+}
+
+void
+CommMonitor::recvRetrySlave()
+{
+    masterPort.sendRetry();
+}
+
+void
+CommMonitor::recvRangeChange()
+{
+    slavePort.sendRangeChange();
+}
+
+void
+CommMonitor::regStats()
+{
+    // Initialise all the monitor stats
+    using namespace Stats;
+
+    stats.readBurstLengthHist
+        .init(params()->burst_length_bins)
+        .name(name() + ".readBurstLengthHist")
+        .desc("Histogram of burst lengths of transmitted packets")
+        .flags(stats.disableBurstLengthHists ? nozero : pdf);
+
+    stats.writeBurstLengthHist
+        .init(params()->burst_length_bins)
+        .name(name() + ".writeBurstLengthHist")
+        .desc("Histogram of burst lengths of transmitted packets")
+        .flags(stats.disableBurstLengthHists ? nozero : pdf);
+
+    // Stats based on received responses
+    stats.readBandwidthHist
+        .init(params()->bandwidth_bins)
+        .name(name() + ".readBandwidthHist")
+        .desc("Histogram of read bandwidth per sample period (bytes/s)")
+        .flags(stats.disableBandwidthHists ? nozero : pdf);
+
+    stats.averageReadBW
+        .name(name() + ".averageReadBandwidth")
+        .desc("Average read bandwidth (bytes/s)")
+        .flags(stats.disableBandwidthHists ? nozero : pdf);
+
+    stats.totalReadBytes
+        .name(name() + ".totalReadBytes")
+        .desc("Number of bytes read")
+        .flags(stats.disableBandwidthHists ? nozero : pdf);
+
+    stats.averageReadBW = stats.totalReadBytes / simSeconds;
+
+    // Stats based on successfully sent requests
+    stats.writeBandwidthHist
+        .init(params()->bandwidth_bins)
+        .name(name() + ".writeBandwidthHist")
+        .desc("Histogram of write bandwidth (bytes/s)")
+        .flags(stats.disableBandwidthHists ? (pdf | nozero) : pdf);
+
+    stats.averageWriteBW
+        .name(name() + ".averageWriteBandwidth")
+        .desc("Average write bandwidth (bytes/s)")
+        .flags(stats.disableBandwidthHists ? nozero : pdf);
+
+    stats.totalWrittenBytes
+        .name(name() + ".totalWrittenBytes")
+        .desc("Number of bytes written")
+        .flags(stats.disableBandwidthHists ? nozero : pdf);
+
+    stats.averageWriteBW = stats.totalWrittenBytes / simSeconds;
+
+    stats.readLatencyHist
+        .init(params()->latency_bins)
+        .name(name() + ".readLatencyHist")
+        .desc("Read request-response latency")
+        .flags(stats.disableLatencyHists ? nozero : pdf);
+
+    stats.writeLatencyHist
+        .init(params()->latency_bins)
+        .name(name() + ".writeLatencyHist")
+        .desc("Write request-response latency")
+        .flags(stats.disableLatencyHists ? nozero : pdf);
+
+    stats.ittReadRead
+        .init(1, params()->itt_max_bin, params()->itt_max_bin /
+              params()->itt_bins)
+        .name(name() + ".ittReadRead")
+        .desc("Read-to-read inter transaction time")
+        .flags(stats.disableITTDists ? nozero : pdf);
+
+    stats.ittWriteWrite
+        .init(1, params()->itt_max_bin, params()->itt_max_bin /
+              params()->itt_bins)
+        .name(name() + ".ittWriteWrite")
+        .desc("Write-to-write inter transaction time")
+        .flags(stats.disableITTDists ? nozero : pdf);
+
+    stats.ittReqReq
+        .init(1, params()->itt_max_bin, params()->itt_max_bin /
+              params()->itt_bins)
+        .name(name() + ".ittReqReq")
+        .desc("Request-to-request inter transaction time")
+        .flags(stats.disableITTDists ? nozero : pdf);
+
+    stats.outstandingReadsHist
+        .init(params()->outstanding_bins)
+        .name(name() + ".outstandingReadsHist")
+        .desc("Outstanding read transactions")
+        .flags(stats.disableOutstandingHists ? nozero : pdf);
+
+    stats.outstandingWritesHist
+        .init(params()->outstanding_bins)
+        .name(name() + ".outstandingWritesHist")
+        .desc("Outstanding write transactions")
+        .flags(stats.disableOutstandingHists ? nozero : pdf);
+
+    stats.readTransHist
+        .init(params()->transaction_bins)
+        .name(name() + ".readTransHist")
+        .desc("Histogram of read transactions per sample period")
+        .flags(stats.disableTransactionHists ? nozero : pdf);
+
+    stats.writeTransHist
+        .init(params()->transaction_bins)
+        .name(name() + ".writeTransHist")
+        .desc("Histogram of read transactions per sample period")
+        .flags(stats.disableTransactionHists ? nozero : pdf);
+
+    stats.readAddrDist
+        .init(0)
+        .name(name() + ".readAddrDist")
+        .desc("Read address distribution")
+        .flags(stats.disableAddrDists ? nozero : pdf);
+
+    stats.writeAddrDist
+        .init(0)
+        .name(name() + ".writeAddrDist")
+        .desc("Write address distribution")
+        .flags(stats.disableAddrDists ? nozero : pdf);
+}
+
+void
+CommMonitor::samplePeriodic()
+{
+    // the periodic stats update runs on the granularity of sample
+    // periods, but in combination with this there may also be a
+    // external resets and dumps of the stats (through schedStatEvent)
+    // causing the stats themselves to capture less than a sample
+    // period
+
+    // only capture if we have not reset the stats during the last
+    // sample period
+    if (simTicks.value() >= samplePeriodTicks) {
+        if (!stats.disableTransactionHists) {
+            stats.readTransHist.sample(stats.readTrans);
+            stats.writeTransHist.sample(stats.writeTrans);
+        }
+
+        if (!stats.disableBandwidthHists) {
+            stats.readBandwidthHist.sample(stats.readBytes / samplePeriod);
+            stats.writeBandwidthHist.sample(stats.writtenBytes / samplePeriod);
+        }
+
+        if (!stats.disableOutstandingHists) {
+            stats.outstandingReadsHist.sample(stats.outstandingReadReqs);
+            stats.outstandingWritesHist.sample(stats.outstandingWriteReqs);
+        }
+    }
+
+    // reset the sampled values
+    stats.readTrans = 0;
+    stats.writeTrans = 0;
+
+    stats.readBytes = 0;
+    stats.writtenBytes = 0;
+
+    schedule(samplePeriodicEvent, curTick() + samplePeriodTicks);
+}
+
+void
+CommMonitor::startup()
+{
+    schedule(samplePeriodicEvent, curTick() + samplePeriodTicks);
+}