mem: Redesign the stack distance calculator as a probe

This changeset removes the stack distance calculator hooks from the
CommMonitor class and implements a stack distance calculator as a
memory system probe instead. The probe can be hooked up to any
component that exports probe points of the type ProbePoints::Packet.

11 files changed, 288 insertions, 168 deletions

diff --git a/src/mem/CommMonitor.py b/src/mem/CommMonitor.py
index a87b04787..ba871357d 100644
--- a/src/mem/CommMonitor.py
+++ b/src/mem/CommMonitor.py
@@ -110,6 +110,3 @@ class CommMonitor(MemObject):
     read_addr_mask = Param.Addr(MaxAddr, "Address mask for read address")
     write_addr_mask = Param.Addr(MaxAddr, "Address mask for write address")
     disable_addr_dists = Param.Bool(True, "Disable address distributions")
-
-    # optional stack distance calculator
-    stack_dist_calc = Param.StackDistCalc(NULL, "Stack distance calculator")
diff --git a/src/mem/SConscript b/src/mem/SConscript
index 50f58add1..4f1216745 100644
--- a/src/mem/SConscript
+++ b/src/mem/SConscript
@@ -44,7 +44,6 @@ SimObject('ExternalMaster.py')
 SimObject('ExternalSlave.py')
 SimObject('MemObject.py')
 SimObject('SimpleMemory.py')
-SimObject('StackDistCalc.py')
 SimObject('XBar.py')
 
 Source('abstract_mem.cc')
diff --git a/src/mem/comm_monitor.cc b/src/mem/comm_monitor.cc
index bd9b26816..35f4738d6 100644
--- a/src/mem/comm_monitor.cc
+++ b/src/mem/comm_monitor.cc
@@ -55,7 +55,6 @@ CommMonitor::CommMonitor(Params* params)
       samplePeriod(params->sample_period / SimClock::Float::s),
       readAddrMask(params->read_addr_mask),
       writeAddrMask(params->write_addr_mask),
-      stackDistCalc(params->stack_dist_calc),
       system(params->system),
       traceStream(nullptr),
       stats(params)
@@ -183,10 +182,6 @@ CommMonitor::recvAtomic(PacketPtr pkt)
 {
     ppPktReq->notify(pkt);
 
-    // do stack distance calculations if enabled
-    if (stackDistCalc)
-        stackDistCalc->update(pkt->cmd, pkt->getAddr());
-
     // if tracing enabled, store the packet information
     // to the trace stream
     if (traceStream != NULL) {
@@ -258,11 +253,6 @@ CommMonitor::recvTimingReq(PacketPtr pkt)
         pkt->cmd = response_cmd;
     }
 
-    // If successful and we are calculating stack distances, update
-    // the calculator
-    if (successful && stackDistCalc)
-        stackDistCalc->update(cmd, addr);
-
     if (successful && traceStream != NULL) {
         // Create a protobuf message representing the
         // packet. Currently we do not preserve the flags in the
diff --git a/src/mem/comm_monitor.hh b/src/mem/comm_monitor.hh
index 941de23ab..d2ce1d224 100644
--- a/src/mem/comm_monitor.hh
+++ b/src/mem/comm_monitor.hh
@@ -43,7 +43,6 @@
 
 #include "base/statistics.hh"
 #include "mem/mem_object.hh"
-#include "mem/stack_dist_calc.hh"
 #include "params/CommMonitor.hh"
 #include "proto/protoio.hh"
 #include "sim/probe/mem.hh"
@@ -417,9 +416,6 @@ class CommMonitor : public MemObject
     /** Address mask for sources of write accesses to be captured */
     const Addr writeAddrMask;
 
-    /** Optional stack distance calculator */
-    StackDistCalc *const stackDistCalc;
-
     /** The system in which the monitor lives */
     System *const system;
 
diff --git a/src/mem/probes/SConscript b/src/mem/probes/SConscript
index 3fe5752cc..7391545fb 100644
--- a/src/mem/probes/SConscript
+++ b/src/mem/probes/SConscript
@@ -41,3 +41,6 @@ Import('*')
 
 SimObject('BaseMemProbe.py')
 Source('base.cc')
+
+SimObject('StackDistProbe.py')
+Source('stack_dist.cc')
diff --git a/src/mem/StackDistCalc.py b/src/mem/probes/StackDistProbe.py
index 4986da9be..431e86463 100644
--- a/src/mem/StackDistCalc.py
+++ b/src/mem/probes/StackDistProbe.py
@@ -1,4 +1,4 @@
-# Copyright (c) 2014 ARM Limited
+# Copyright (c) 2014-2015 ARM Limited
 # All rights reserved.
 #
 # The license below extends only to copyright in the software and shall
@@ -34,13 +34,23 @@
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #
 # Authors: Andreas Hansson
+#          Andreas Sandberg
 
-from m5.SimObject import SimObject
 from m5.params import *
+from m5.proxy import *
+from BaseMemProbe import BaseMemProbe
 
-class StackDistCalc(SimObject):
-    type = 'StackDistCalc'
-    cxx_header = "mem/stack_dist_calc.hh"
+class StackDistProbe(BaseMemProbe):
+    type = 'StackDistProbe'
+    cxx_header = "mem/probes/stack_dist.hh"
+
+    system = Param.System(Parent.any,
+                          "System to use when determining system cache "
+                          "line size")
+
+    line_size = Param.Unsigned(Parent.cache_line_size,
+                               "Cache line size in bytes (must be larger or "
+                               "equal to the system's line size)")
 
     # enable verification stack
     verify = Param.Bool(False, "Verify behaviuor with reference implementation")
diff --git a/src/mem/probes/stack_dist.cc b/src/mem/probes/stack_dist.cc
new file mode 100644
index 000000000..c742cae7b
--- /dev/null
+++ b/src/mem/probes/stack_dist.cc
@@ -0,0 +1,138 @@
+/*
+ * Copyright (c) 2015 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: Andreas Sandberg
+ */
+
+#include "mem/probes/stack_dist.hh"
+
+#include "params/StackDistProbe.hh"
+#include "sim/system.hh"
+
+StackDistProbe::StackDistProbe(StackDistProbeParams *p)
+    : BaseMemProbe(p),
+      lineSize(p->line_size),
+      disableLinearHists(p->disable_linear_hists),
+      disableLogHists(p->disable_log_hists),
+      calc(p->verify)
+{
+    fatal_if(p->system->cacheLineSize() > p->line_size,
+             "The stack distance probe must use a cache line size that is "
+             "larger or equal to the system's cahce line size.");
+}
+
+void
+StackDistProbe::regStats()
+{
+    const StackDistProbeParams *p(
+        dynamic_cast<const StackDistProbeParams *>(params()));
+    assert(p);
+
+    using namespace Stats;
+
+    readLinearHist
+        .init(p->linear_hist_bins)
+        .name(name() + ".readLinearHist")
+        .desc("Reads linear distribution")
+        .flags(disableLinearHists ? nozero : pdf);
+
+    readLogHist
+        .init(p->log_hist_bins)
+        .name(name() + ".readLogHist")
+        .desc("Reads logarithmic distribution")
+        .flags(disableLogHists ? nozero : pdf);
+
+    writeLinearHist
+        .init(p->linear_hist_bins)
+        .name(name() + ".writeLinearHist")
+        .desc("Writes linear distribution")
+        .flags(disableLinearHists ? nozero : pdf);
+
+    writeLogHist
+        .init(p->log_hist_bins)
+        .name(name() + ".writeLogHist")
+        .desc("Writes logarithmic distribution")
+        .flags(disableLogHists ? nozero : pdf);
+
+    infiniteSD
+        .name(name() + ".infinity")
+        .desc("Number of requests with infinite stack distance")
+        .flags(nozero);
+}
+
+void
+StackDistProbe::handleRequest(const PacketPtr &pkt)
+{
+    // only capturing read and write requests (which allocate in the
+    // cache)
+    if (!pkt->isRead() && !pkt->isWrite())
+        return;
+
+    // Align the address to a cache line size
+    const Addr aligned_addr(roundDown(pkt->getAddr(), lineSize));
+
+    // Calculate the stack distance
+    const uint64_t sd(calc.calcStackDistAndUpdate(aligned_addr).first);
+    if (sd == StackDistCalc::Infinity) {
+        infiniteSD++;
+        return;
+    }
+
+    // Sample the stack distance of the address in linear bins
+    if (!disableLinearHists) {
+        if (pkt->isRead())
+            readLinearHist.sample(sd);
+        else
+            writeLinearHist.sample(sd);
+    }
+
+    if (!disableLogHists) {
+        int sd_lg2 = sd == 0 ? 1 : floorLog2(sd);
+
+        // Sample the stack distance of the address in log bins
+        if (pkt->isRead())
+            readLogHist.sample(sd_lg2);
+        else
+            writeLogHist.sample(sd_lg2);
+    }
+}
+
+
+StackDistProbe *
+StackDistProbeParams::create()
+{
+    return new StackDistProbe(this);
+}
diff --git a/src/mem/probes/stack_dist.hh b/src/mem/probes/stack_dist.hh
new file mode 100644
index 000000000..210800894
--- /dev/null
+++ b/src/mem/probes/stack_dist.hh
@@ -0,0 +1,91 @@
+/*
+ * Copyright (c) 2015 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: Andreas Sandberg
+ */
+
+#ifndef __MEM_PROBES_STACK_DIST_HH__
+#define __MEM_PROBES_STACK_DIST_HH__
+
+#include "mem/packet.hh"
+#include "mem/probes/base.hh"
+#include "mem/stack_dist_calc.hh"
+#include "sim/stats.hh"
+
+struct StackDistProbeParams;
+
+class StackDistProbe : public BaseMemProbe
+{
+  public:
+    StackDistProbe(StackDistProbeParams *params);
+
+    void regStats() M5_ATTR_OVERRIDE;
+
+  protected:
+    void handleRequest(const PacketPtr &pkt) M5_ATTR_OVERRIDE;
+
+  protected:
+    // Cache line size to simulate
+    const unsigned lineSize;
+
+    // Disable the linear histograms
+    const bool disableLinearHists;
+
+    // Disable the logarithmic histograms
+    const bool disableLogHists;
+
+  protected:
+    // Reads linear histogram
+    Stats::Histogram readLinearHist;
+
+    // Reads logarithmic histogram
+    Stats::SparseHistogram readLogHist;
+
+    // Writes linear histogram
+    Stats::Histogram writeLinearHist;
+
+    // Writes logarithmic histogram
+    Stats::SparseHistogram writeLogHist;
+
+    // Writes logarithmic histogram
+    Stats::Scalar infiniteSD;
+
+  protected:
+    StackDistCalc calc;
+};
+
+
+#endif //__MEM_PROBES_STACK_DIST_HH__
diff --git a/src/mem/stack_dist_calc.cc b/src/mem/stack_dist_calc.cc
index c273ee7f4..3dca87384 100644
--- a/src/mem/stack_dist_calc.cc
+++ b/src/mem/stack_dist_calc.cc
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014 ARM Limited
+ * Copyright (c) 2014-2015 ARM Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
@@ -37,15 +37,16 @@
  * Authors: Kanishk Sugand
  */
 
+#include "mem/stack_dist_calc.hh"
+
+#include "base/chunk_generator.hh"
 #include "base/intmath.hh"
 #include "base/trace.hh"
 #include "debug/StackDist.hh"
-#include "mem/stack_dist_calc.hh"
 
-StackDistCalc::StackDistCalc(const StackDistCalcParams* p) :
-    SimObject(p), index(0), verifyStack(p->verify),
-    disableLinearHists(p->disable_linear_hists),
-    disableLogHists(p->disable_log_hists)
+StackDistCalc::StackDistCalc(bool verify_stack)
+    : index(0),
+      verifyStack(verify_stack)
 {
     // Instantiate a new root and leaf layer
     // Map type variable, representing a layer in the tree
@@ -91,38 +92,6 @@ StackDistCalc::~StackDistCalc()
     stack.clear();
 }
 
-void
-StackDistCalc::update(const MemCmd& cmd, Addr addr)
-{
-    // only capturing read and write requests (which allocate in the
-    // cache)
-    if (cmd.isRead() || cmd.isWrite()) {
-        auto returnType = calcStackDistAndUpdate(addr);
-
-        uint64_t stackDist = returnType.first;
-
-        if (stackDist != Infinity) {
-            // Sample the stack distance of the address in linear bins
-            if (!disableLinearHists) {
-                if (cmd.isRead())
-                    readLinearHist.sample(stackDist);
-                else
-                    writeLinearHist.sample(stackDist);
-            }
-
-            if (!disableLogHists) {
-                int stackDistLog2 = stackDist == 0 ? 1 : floorLog2(stackDist);
-
-                // Sample the stack distance of the address in log bins
-                if (cmd.isRead())
-                    readLogHist.sample(stackDistLog2);
-                else
-                    writeLogHist.sample(stackDistLog2);
-            }
-        }
-    }
-}
-
 // The updateSum method is a recursive function which updates
 // the node sums till the root. It also deletes the nodes that
 // are not used anymore.
@@ -632,39 +601,3 @@ StackDistCalc::printStack(int n) const
         }
     }
 }
-
-void
-StackDistCalc::regStats()
-{
-    using namespace Stats;
-
-    readLinearHist
-        .init(params()->linear_hist_bins)
-        .name(name() + ".readLinearHist")
-        .desc("Reads linear distribution")
-        .flags(disableLinearHists ? nozero : pdf);
-
-    readLogHist
-        .init(params()->log_hist_bins)
-        .name(name() + ".readLogHist")
-        .desc("Reads logarithmic distribution")
-        .flags(disableLogHists ? nozero : pdf);
-
-    writeLinearHist
-        .init(params()->linear_hist_bins)
-        .name(name() + ".writeLinearHist")
-        .desc("Writes linear distribution")
-        .flags(disableLinearHists ? nozero : pdf);
-
-    writeLogHist
-        .init(params()->log_hist_bins)
-        .name(name() + ".writeLogHist")
-        .desc("Writes logarithmic distribution")
-        .flags(disableLogHists ? nozero : pdf);
-}
-
-StackDistCalc*
-StackDistCalcParams::create()
-{
-    return new StackDistCalc(this);
-}
diff --git a/src/mem/stack_dist_calc.hh b/src/mem/stack_dist_calc.hh
index 881b71179..6dfc93b99 100644
--- a/src/mem/stack_dist_calc.hh
+++ b/src/mem/stack_dist_calc.hh
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014 ARM Limited
+ * Copyright (c) 2014-2015 ARM Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
@@ -41,14 +41,11 @@
 #ifndef __MEM_STACK_DIST_CALC_HH__
 #define __MEM_STACK_DIST_CALC_HH__
 
+#include <limits>
 #include <map>
 #include <vector>
 
 #include "base/types.hh"
-#include "mem/packet.hh"
-#include "params/StackDistCalc.hh"
-#include "sim/sim_object.hh"
-#include "sim/stats.hh"
 
 /**
   * The stack distance calculator is a passive object that merely
@@ -174,7 +171,7 @@
   * A printStack(int numOfEntitiesToPrint) is provided to print top n entities
   * in both (tree and STL based dummy stack).
   */
-class StackDistCalc : public SimObject
+class StackDistCalc
 {
 
   private:
@@ -267,39 +264,6 @@ class StackDistCalc : public SimObject
     void sanityCheckTree(const Node* node, uint64_t level = 0) const;
 
     /**
-     * A convenient way of refering to infinity.
-     */
-    static constexpr uint64_t Infinity = std::numeric_limits<uint64_t>::max();
-
-    /**
-     * Process the given address. If Mark is true then set the
-     * mark flag of the leaf node.
-     * This function returns the stack distance of the incoming
-     * address and the previous status of the mark flag.
-     *
-     * @param r_address The current address to process
-     * @param mark set the mark flag for the address.
-     * @return The stack distance of the current address and the mark flag.
-     */
-    std::pair<uint64_t , bool> calcStackDist(const Addr r_address,
-                                             bool mark = false);
-
-    /**
-     * Process the given address:
-     *  - Lookup the tree for the given address
-     *  - delete old node if found in tree
-     *  - add a new node (if addNewNode flag is set)
-     * This function returns the stack distance of the incoming
-     * address and the status of the mark flag.
-     *
-     * @param r_address The current address to process
-     * @param addNewNode If true, a new node is added to the tree
-     * @return The stack distance of the current address and the mark flag.
-     */
-    std::pair<uint64_t, bool> calcStackDistAndUpdate(const Addr r_address,
-                                                     bool addNewNode = true);
-
-    /**
      * Return the counter for address accesses (unique and
      * non-unique). This is further used to dump stats at
      * regular intervals.
@@ -341,26 +305,43 @@ class StackDistCalc : public SimObject
                              bool update_stack = false);
 
   public:
+    StackDistCalc(bool verify_stack = false);
+
+    ~StackDistCalc();
 
     /**
-     * Convenience method to get the params when registering stats.
+     * A convenient way of refering to infinity.
      */
-    const StackDistCalcParams* params() const
-    { return reinterpret_cast<const StackDistCalcParams*>(_params); }
+    static constexpr uint64_t Infinity = std::numeric_limits<uint64_t>::max();
 
-    StackDistCalc(const StackDistCalcParams* p);
 
-    ~StackDistCalc();
-
-    void regStats();
+    /**
+     * Process the given address. If Mark is true then set the
+     * mark flag of the leaf node.
+     * This function returns the stack distance of the incoming
+     * address and the previous status of the mark flag.
+     *
+     * @param r_address The current address to process
+     * @param mark set the mark flag for the address.
+     * @return The stack distance of the current address and the mark flag.
+     */
+    std::pair<uint64_t, bool> calcStackDist(const Addr r_address,
+                                            bool mark = false);
 
     /**
-     * Update the tree and the statistics.
+     * Process the given address:
+     *  - Lookup the tree for the given address
+     *  - delete old node if found in tree
+     *  - add a new node (if addNewNode flag is set)
+     * This function returns the stack distance of the incoming
+     * address and the status of the mark flag.
      *
-     * @param cmd Command from the packet
-     * @param addr Address to put on the stack
+     * @param r_address The current address to process
+     * @param addNewNode If true, a new node is added to the tree
+     * @return The stack distance of the current address and the mark flag.
      */
-    void update(const MemCmd& cmd, Addr addr);
+    std::pair<uint64_t, bool> calcStackDistAndUpdate(const Addr r_address,
+                                                     bool addNewNode = true);
 
   private:
 
@@ -430,25 +411,7 @@ class StackDistCalc : public SimObject
 
     // Flag to enable verification of stack. (Slows down the simulation)
     const bool verifyStack;
-
-    // Disable the linear histograms
-    const bool disableLinearHists;
-
-    // Disable the logarithmic histograms
-    const bool disableLogHists;
-
-    // Reads linear histogram
-    Stats::Histogram readLinearHist;
-
-    // Reads logarithmic histogram
-    Stats::SparseHistogram readLogHist;
-
-    // Writes linear histogram
-    Stats::Histogram writeLinearHist;
-
-    // Writes logarithmic histogram
-    Stats::SparseHistogram writeLogHist;
-
 };
 
+
 #endif //__STACK_DIST_CALC_HH__
diff --git a/tests/configs/tgen-simple-mem.py b/tests/configs/tgen-simple-mem.py
index edb2f9fcd..8c2aa80a9 100644
--- a/tests/configs/tgen-simple-mem.py
+++ b/tests/configs/tgen-simple-mem.py
@@ -57,8 +57,8 @@ system = System(cpu = cpu, physmem = SimpleMemory(),
 # add a communication monitor, and also trace all the packets and
 # calculate and verify stack distance
 system.monitor = CommMonitor(trace_file = "monitor.ptrc.gz",
-                             trace_enable = True,
-                             stack_dist_calc = StackDistCalc(verify = True))
+                             trace_enable = True)
+system.monitor.stackdist = StackDistProbe(verify = True)
 
 # connect the traffic generator to the bus via a communication monitor
 system.cpu.port = system.monitor.slave