mem: Add a stack distance calculator

This patch adds a stand-alone stack distance calculator. The stack
distance calculator is a passive SimObject that observes the addresses
passed to it. It calculates stack distances (LRU Distances) of
incoming addresses based on the partial sum hierarchy tree algorithm
described by Alamasi et al. http://doi.acm.org/10.1145/773039.773043.

For each transaction a hashtable look-up is performed. At every
non-unique transaction the tree is traversed from the leaf at the
returned index to the root, the old node is deleted from the tree, and
the sums (to the right) are collected and decremented. The collected
sum represets the stack distance of the found node. At every unique
transaction the stack distance is returned as
numeric_limits<uint64>::max().

In addition to the basic stack distance calculation, a feature to mark
an old node in the tree is added. This is useful if it is required to
see the reuse pattern. For example, Writebacks to the lower level
(e.g. membus from L2), can be marked instead of being removed from the
stack (isMarked flag of Node set to True). And then later if this same
address is accessed (by L1), the value of the isMarked flag would be
True. This gives some insight on how the Writeback policy of the
lower level affect the read/write accesses in an application.

Debugging is enabled by setting the verify flag to true. Debugging is
implemented using a dummy stack that behaves in a naive way, using STL
vectors. Note that this has a large impact on run time.

1 files changed, 454 insertions, 0 deletions

diff --git a/src/mem/stack_dist_calc.hh b/src/mem/stack_dist_calc.hh
new file mode 100644
index 000000000..881b71179
--- /dev/null
+++ b/src/mem/stack_dist_calc.hh
@@ -0,0 +1,454 @@
+/*
+ * Copyright (c) 2014 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: Kanishk Sugand
+ *          Andreas Hansson
+ */
+
+#ifndef __MEM_STACK_DIST_CALC_HH__
+#define __MEM_STACK_DIST_CALC_HH__
+
+#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
+  * observes the addresses pass to it. It calculates stack distances
+  * of incoming addresses based on the partial sum hierarchy tree
+  * algorithm described by Alamasi et al.
+  * http://doi.acm.org/10.1145/773039.773043.
+  *
+  * A tree structure is maintained and updated at each transaction
+  * (unique or non-unique). The tree is implemented as an STL vector
+  * with layers of the form <map> Each layer in this tree is an
+  * ordered map <uint64_t, Node*>. Nodes are structs which take form
+  * of leaf, intermediate and root nodes. For example, in a tree with 3
+  * layers, tree[0][5] gives a leaf node pointer for key=5 tree[1][1]
+  * gives an intermediate node pointer for key=1 tree[2][0] gives the
+  * root node in the tree.
+  *
+  * At every transaction a hash-map (aiMap) is looked up to check if
+  * the address was already encountered before. Based on this lookup a
+  * transaction can be termed as unique or non-unique.
+  *
+  * In addition to the normal stack distance calculation, a feature to
+  * mark an old node in the tree is added. This is useful if it is
+  * required to see the reuse pattern. For example, BackInvalidates
+  * from a lower level (e.g. membus to L2), can be marked (isMarked
+  * flag of Node set to True). Then later if this same address is
+  * accessed (by L1), the value of the isMarked flag would be
+  * True. This would give some insight on how the BackInvalidates
+  * policy of the lower level affect the read/write accesses in an
+  * application.
+  *
+  * There are two functions provided to interface with the calculator:
+  * 1. pair<uint64_t, bool> calcStackDistAndUpdate(Addr r_address,
+  *                                                bool addNewNode)
+  * At every unique transaction a new leaf node is added at tree[0](leaf layer)
+  * and linked to the layer above (if addNewNode is True). The sums of all
+  * the intermediate nodes is updated till the root. The stack-distance is
+  * returned as a Constant representing INFINITY.
+  *
+  * At every non-unique transaction the tree is traversed from the
+  * leaf at the returned index to the root, the old node is deleted
+  * from the tree, and the sums (to the right are collected) and
+  * decremented. The collected sum represets the stack distance of the
+  * found node. If this node was marked then a bool flag set to True
+  * is returned with the stack_distance. During this operation a node
+  * is discarded at the leaf layer always. Moreover during the
+  * traversal upwards using the updateSum() method, if an intermediate
+  * node is found with no children connected to it, then that is
+  * discarded too.
+  *
+  * The return value of this function is a pair representing the
+  * stack_distance and the value of the marked flag.
+  *
+  * 2. pair<uint64_t , bool> calcStackDist(Addr r_address, bool mark)
+  * This is a stripped down version of the above function which is used to
+  * just inspect the tree, and mark a leaf node (if mark flag is set). The
+  * functionality to add a new node is removed.
+  *
+  * At every unique transaction the stack-distance is returned as a constant
+  * representing INFINITY.
+  *
+  * At every non-unique transaction the tree is traversed from the
+  * leaf at the returned index to the root, and the sums (to the right)
+  * are collected. The collected sum represets the stack distance of
+  * the found node.
+  *
+  * This function does NOT Modify the stack. (No node is added or
+  * deleted).  It is just used to mark a node already created and get
+  * its stack distance.
+  *
+  * The return value of this function is a pair representing the stack
+  * distance and the value of the marked flag.
+  *
+  * The table below depicts the usage of the Algorithm using the functions:
+  * pair<uint64_t Stack_dist, bool isMarked> calcStackDistAndUpdate
+  *                                      (Addr r_address, bool addNewNode)
+  * pair<uint64_t Stack_dist, bool isMarked> calcStackDist
+  *                                              (Addr r_address, bool mark)
+  *
+  * |   Function           |   Arguments   |Return Val |Use For|
+  * |calcStackDistAndUpdate|r_address, True|I/SD,False |A,GD,GM|
+  * |calcStackDistAndUpdate|r_address,False|SD,prevMark|D,GD,GM|
+  * |calcStackDist         |r_address,False|SD,prevMark|  GD,GM|
+  * |calcStackDist         |r_address, True|SD,prevMark|  GD,GM|
+  *
+  * (*A: Allocate an address in stack, if old entry present then it is deleted,
+  *  *U: Delete old-address from stack, no new entry is added
+  *  *GD: Get-Stack distance of an address,
+  *  *GM: Get value of Mark flag, indicates if that address has been touched
+  *                                                                  before,
+  *  *I: stack-distance = infinity,
+  *  *SD: Stack Distance
+  *  *r_address: address to be added, *prevMark: value of isMarked flag
+  *                                                              of the Node)
+  *
+  * Invalidates refer to a type of packet that removes something from
+  * a cache, either autonoumously (due-to cache's own replacement
+  * policy), or snoops from other caches which invalidate something
+  * inside our cache.
+  *
+  * Usage            |   Function to use    |Typical Use           |
+  * Add new entry    |calcStackDistAndUpdate|Read/Write Allocate   |
+  * Delete Old Entry |calcStackDistAndUpdate|Writebacks/Cleanevicts|
+  * Dist.of Old entry|calcStackDist         |Cleanevicts/Invalidate|
+  *
+  * Node Balancing: The tree structure is maintained by an
+  * updateTree() operation called when an intermediate node is
+  * required. The update operation is roughly categorized as a root
+  * update or intermediate layer update. When number of leaf nodes
+  * grow over a power of 2 then a new layer is added at the top of the
+  * tree and a new root node is initialized. The old node at the lower
+  * layer is connected to this.  In an intermediate node update
+  * operation a new intermediate node is added to the required layer.
+  *
+  * Debugging: Debugging can be enabled by setting the verifyStack flag
+  * true. Debugging is implemented using a dummy stack that behaves in
+  * a naive way, using STL vectors (i.e each unique address is pushed
+  * on the top of an STL vector stack, and SD is returned as
+  * Infinity. If a non unique address is encountered then the previous
+  * entry in the STL vector is removed, all the entities above it are
+  * pushed down, and the address is pushed at the top of the stack).
+  *
+  * A printStack(int numOfEntitiesToPrint) is provided to print top n entities
+  * in both (tree and STL based dummy stack).
+  */
+class StackDistCalc : public SimObject
+{
+
+  private:
+
+    struct Node;
+
+    typedef std::map<uint64_t, Node*> IndexNodeMap;
+    typedef std::map<Addr, uint64_t> AddressIndexMap;
+    typedef std::vector<IndexNodeMap> TreeType;
+
+    /**
+     * Gets sum from the node upwards recursively till the root.  This
+     * function is called first by getSumsLeavesToRoot, and then
+     * recursively calls itself.
+     *
+     * @param node pointer to the node which is updated
+     * @param from_left variable which says that the request arrived
+     *        from the left
+     * @param sum_from_below Sum of left and right children below
+     * @param level level in the tree the calling node is located
+     * @param stack_dist stack distance of the node below
+     * @return The stack distance of the current address.
+     *
+     */
+    uint64_t getSum(Node* node, bool from_left, uint64_t sum_from_below,
+                    uint64_t stack_dist, uint64_t level) const;
+
+    /**
+     * Gets the sum from the leaf node specified. This function
+     * is called by calcStackDist.
+     *
+     * @param node pointer to the node which is updated
+     * @return The stack distance of the current address.
+     *
+     */
+    uint64_t getSumsLeavesToRoot(Node* node) const;
+
+    /**
+     * Updates the nodes upwards recursively till the root.
+     * This function is first called by updateSumsLeavesToRoot,
+     * and then it recursively calls itself.
+     *
+     * @param node pointer to the node which is updated
+     * @param from_left variable which says that the request arrived
+     * from the left
+     * @param sum_from_below Sum of left and right children below
+     * @param level level in the tree the calling node is located
+     * @param stack_dist stack distance of the node below
+     * @param discard_node whether the calling node was discarded or not
+     * @return The stack distance of the current address.
+     *
+     */
+    uint64_t updateSum(Node* node,
+                       bool from_left, uint64_t sum_from_below, uint64_t level,
+                       uint64_t stack_dist, bool discard_node);
+
+    /**
+     * Updates the leaf nodes and nodes above. This function is
+     * called by the calcStackDistAndUpdate.
+     *
+     * @param node pointer to the node which is updated
+     * @param is_new_leaf is true if this is a newly added node
+     * @return The stack distance of the current address.
+     *
+     */
+    uint64_t updateSumsLeavesToRoot(Node* node, bool is_new_leaf);
+
+    /**
+     * updateTree is a tree balancing operation, which maintains the
+     * binary tree structure.
+     * This method is called whenever index%2 == 0 (i.e. every
+     * alternate cycle) The two main operation are :
+     * OP1. Moving the root node one layer up if index counter
+     *       crosses power of 2
+     * OP2. Addition of intermediate nodes as and when required
+     *      and linking them to their parents in the layer above.
+     */
+    void updateTree();
+
+    /**
+     * This method is used for verification purposes
+     * It recursively traverses upwards from the given node till
+     * the root to check if the ultimate parent node (root-node) points
+     * to null.
+     *
+     * @param node pointer to the node whose sanity is being checked
+     * @param level the level at which this node is located in the tree
+     *
+     */
+    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.
+     *
+     * @return The stack distance of the current address.
+     */
+    uint64_t getIndex() const { return index; }
+
+    /**
+     * Query depth of the tree (tree[0] represents leaf layer while
+     * tree[treeDepth] represents the root layer, all layers in
+     * between contain intermediate nodes)
+     *
+     * @return Tree depth
+     */
+    uint64_t getTreeDepth() const { return tree.size() - 1; }
+
+    /**
+     * Print the last n items on the stack.
+     * This method prints top n entries in the tree based implementation as
+     * well as dummy stack.
+     * @param n Number of entries to print
+     */
+    void printStack(int n = 5) const;
+
+    /**
+     * This is an alternative implementation of the stack-distance
+     * in a naive way. It uses simple STL vector to represent the stack.
+     * It can be used in parallel for debugging purposes.
+     * It is 10x slower than the tree based implemenation.
+     *
+     * @param r_address The current address to process
+     * @param update_stack Flag to indicate if stack should be updated
+     * @return  Stack distance which is calculated by this alternative
+     * implementation
+     *
+     */
+    uint64_t verifyStackDist(const Addr r_address,
+                             bool update_stack = false);
+
+  public:
+
+    /**
+     * Convenience method to get the params when registering stats.
+     */
+    const StackDistCalcParams* params() const
+    { return reinterpret_cast<const StackDistCalcParams*>(_params); }
+
+    StackDistCalc(const StackDistCalcParams* p);
+
+    ~StackDistCalc();
+
+    void regStats();
+
+    /**
+     * Update the tree and the statistics.
+     *
+     * @param cmd Command from the packet
+     * @param addr Address to put on the stack
+     */
+    void update(const MemCmd& cmd, Addr addr);
+
+  private:
+
+    /**
+     * Node which takes form of Leaf, INode or Root
+     */
+    struct Node{
+        // Sum of the left children
+        uint64_t sumLeft;
+
+        // Sum of the right children
+        uint64_t sumRight;
+
+        // Flag to indicate that sumLeft has gone from non-zero value to 0
+        bool discardLeft;
+
+        // Flag to indicate that sumRight has gone from non-zero value to 0
+        bool discardRight;
+
+        // Index of the current element in the Map
+        uint64_t nodeIndex;
+
+        // Pointer to the parent
+        Node* parent;
+
+        // Flag to mark the node as the right/left child
+        bool isLeftNode;
+
+        /**
+         * Flag to indicate if this address is marked. Used in case
+         * where stack distance of a touched address is required.
+         */
+        bool isMarked;
+
+        /**
+         * The discard flags are false by default they become true if
+         * the node is reached again in a future lookup.
+         */
+        Node() : sumLeft(0), sumRight(0), discardLeft(false),
+                 discardRight(false), nodeIndex(0),
+                 parent(nullptr), isLeftNode(true), isMarked(false)
+        { }
+    };
+
+    /**
+     * Internal counter for address accesses (unique and non-unique)
+     * This counter increments everytime the calcStackDist() method is
+     * called. This counter is used as a key for the hash- map at the
+     * leaf layer. Practically at every call to the calculator this
+     * counter is incremented and a new leaf node is added in the tree
+     * at the leaf layer using this counter value as the key.
+     */
+    uint64_t index;
+
+    // Binary tree of partial sums
+    TreeType tree;
+
+    // Hash map which returns last seen index of each address
+    AddressIndexMap aiMap;
+
+    // Keeps count of number of the next unique index for each
+    // level in the tree
+    std::vector<uint64_t> nextIndex;
+
+    // Dummy Stack for verification
+    std::vector<uint64_t> stack;
+
+    // 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__