src/mem/stack_dist_calc.hh

   1 /*
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  37
  38 #ifndef __MEM_STACK_DIST_CALC_HH__
  39 #define __MEM_STACK_DIST_CALC_HH__
  40
  41 #include <limits>
  42 #include <map>
  43 #include <vector>
  44
  45 #include "base/types.hh"
  46
  47 /**
  48   * The stack distance calculator is a passive object that merely
  49   * observes the addresses pass to it. It calculates stack distances
  50   * of incoming addresses based on the partial sum hierarchy tree
  51   * algorithm described by Alamasi et al.
  52   * http://doi.acm.org/10.1145/773039.773043.
  53   *
  54   * A tree structure is maintained and updated at each transaction
  55   * (unique or non-unique). The tree is implemented as an STL vector
  56   * with layers of the form <map> Each layer in this tree is an
  57   * ordered map <uint64_t, Node*>. Nodes are structs which take form
  58   * of leaf, intermediate and root nodes. For example, in a tree with 3
  59   * layers, tree[0][5] gives a leaf node pointer for key=5 tree[1][1]
  60   * gives an intermediate node pointer for key=1 tree[2][0] gives the
  61   * root node in the tree.
  62   *
  63   * At every transaction a hash-map (aiMap) is looked up to check if
  64   * the address was already encountered before. Based on this lookup a
  65   * transaction can be termed as unique or non-unique.
  66   *
  67   * In addition to the normal stack distance calculation, a feature to
  68   * mark an old node in the tree is added. This is useful if it is
  69   * required to see the reuse pattern. For example, BackInvalidates
  70   * from a lower level (e.g. membus to L2), can be marked (isMarked
  71   * flag of Node set to True). Then later if this same address is
  72   * accessed (by L1), the value of the isMarked flag would be
  73   * True. This would give some insight on how the BackInvalidates
  74   * policy of the lower level affect the read/write accesses in an
  75   * application.
  76   *
  77   * There are two functions provided to interface with the calculator:
  78   * 1. pair<uint64_t, bool> calcStackDistAndUpdate(Addr r_address,
  79   *                                                bool addNewNode)
  80   * At every unique transaction a new leaf node is added at tree[0](leaf layer)
  81   * and linked to the layer above (if addNewNode is True). The sums of all
  82   * the intermediate nodes is updated till the root. The stack-distance is
  83   * returned as a Constant representing INFINITY.
  84   *
  85   * At every non-unique transaction the tree is traversed from the
  86   * leaf at the returned index to the root, the old node is deleted
  87   * from the tree, and the sums (to the right are collected) and
  88   * decremented. The collected sum represets the stack distance of the
  89   * found node. If this node was marked then a bool flag set to True
  90   * is returned with the stack_distance. During this operation a node
  91   * is discarded at the leaf layer always. Moreover during the
  92   * traversal upwards using the updateSum() method, if an intermediate
  93   * node is found with no children connected to it, then that is
  94   * discarded too.
  95   *
  96   * The return value of this function is a pair representing the
  97   * stack_distance and the value of the marked flag.
  98   *
  99   * 2. pair<uint64_t , bool> calcStackDist(Addr r_address, bool mark)
 100   * This is a stripped down version of the above function which is used to
 101   * just inspect the tree, and mark a leaf node (if mark flag is set). The
 102   * functionality to add a new node is removed.
 103   *
 104   * At every unique transaction the stack-distance is returned as a constant
 105   * representing INFINITY.
 106   *
 107   * At every non-unique transaction the tree is traversed from the
 108   * leaf at the returned index to the root, and the sums (to the right)
 109   * are collected. The collected sum represets the stack distance of
 110   * the found node.
 111   *
 112   * This function does NOT Modify the stack. (No node is added or
 113   * deleted).  It is just used to mark a node already created and get
 114   * its stack distance.
 115   *
 116   * The return value of this function is a pair representing the stack
 117   * distance and the value of the marked flag.
 118   *
 119   * The table below depicts the usage of the Algorithm using the functions:
 120   * pair<uint64_t Stack_dist, bool isMarked> calcStackDistAndUpdate
 121   *                                      (Addr r_address, bool addNewNode)
 122   * pair<uint64_t Stack_dist, bool isMarked> calcStackDist
 123   *                                              (Addr r_address, bool mark)
 124   *
 125   * |   Function           |   Arguments   |Return Val |Use For|
 126   * |calcStackDistAndUpdate|r_address, True|I/SD,False |A,GD,GM|
 127   * |calcStackDistAndUpdate|r_address,False|SD,prevMark|D,GD,GM|
 128   * |calcStackDist         |r_address,False|SD,prevMark|  GD,GM|
 129   * |calcStackDist         |r_address, True|SD,prevMark|  GD,GM|
 130   *
 131   * (*A: Allocate an address in stack, if old entry present then it is deleted,
 132   *  *U: Delete old-address from stack, no new entry is added
 133   *  *GD: Get-Stack distance of an address,
 134   *  *GM: Get value of Mark flag, indicates if that address has been touched
 135   *                                                                  before,
 136   *  *I: stack-distance = infinity,
 137   *  *SD: Stack Distance
 138   *  *r_address: address to be added, *prevMark: value of isMarked flag
 139   *                                                              of the Node)
 140   *
 141   * Invalidates refer to a type of packet that removes something from
 142   * a cache, either autonoumously (due-to cache's own replacement
 143   * policy), or snoops from other caches which invalidate something
 144   * inside our cache.
 145   *
 146   * Usage            |   Function to use    |Typical Use           |
 147   * Add new entry    |calcStackDistAndUpdate|Read/Write Allocate   |
 148   * Delete Old Entry |calcStackDistAndUpdate|Writebacks/Cleanevicts|
 149   * Dist.of Old entry|calcStackDist         |Cleanevicts/Invalidate|
 150   *
 151   * Node Balancing: The tree structure is maintained by an
 152   * updateTree() operation called when an intermediate node is
 153   * required. The update operation is roughly categorized as a root
 154   * update or intermediate layer update. When number of leaf nodes
 155   * grow over a power of 2 then a new layer is added at the top of the
 156   * tree and a new root node is initialized. The old node at the lower
 157   * layer is connected to this.  In an intermediate node update
 158   * operation a new intermediate node is added to the required layer.
 159   *
 160   * Debugging: Debugging can be enabled by setting the verifyStack flag
 161   * true. Debugging is implemented using a dummy stack that behaves in
 162   * a naive way, using STL vectors (i.e each unique address is pushed
 163   * on the top of an STL vector stack, and SD is returned as
 164   * Infinity. If a non unique address is encountered then the previous
 165   * entry in the STL vector is removed, all the entities above it are
 166   * pushed down, and the address is pushed at the top of the stack).
 167   *
 168   * A printStack(int numOfEntitiesToPrint) is provided to print top n entities
 169   * in both (tree and STL based dummy stack).
 170   */
 171 class StackDistCalc
 172 {
 173
 174   private:
 175
 176     struct Node;
 177
 178     typedef std::map<uint64_t, Node*> IndexNodeMap;
 179     typedef std::map<Addr, uint64_t> AddressIndexMap;
 180     typedef std::vector<IndexNodeMap> TreeType;
 181
 182     /**
 183      * Gets sum from the node upwards recursively till the root.  This
 184      * function is called first by getSumsLeavesToRoot, and then
 185      * recursively calls itself.
 186      *
 187      * @param node pointer to the node which is updated
 188      * @param from_left variable which says that the request arrived
 189      *        from the left
 190      * @param sum_from_below Sum of left and right children below
 191      * @param level level in the tree the calling node is located
 192      * @param stack_dist stack distance of the node below
 193      * @return The stack distance of the current address.
 194      *
 195      */
 196     uint64_t getSum(Node* node, bool from_left, uint64_t sum_from_below,
 197                     uint64_t stack_dist, uint64_t level) const;
 198
 199     /**
 200      * Gets the sum from the leaf node specified. This function
 201      * is called by calcStackDist.
 202      *
 203      * @param node pointer to the node which is updated
 204      * @return The stack distance of the current address.
 205      *
 206      */
 207     uint64_t getSumsLeavesToRoot(Node* node) const;
 208
 209     /**
 210      * Updates the nodes upwards recursively till the root.
 211      * This function is first called by updateSumsLeavesToRoot,
 212      * and then it recursively calls itself.
 213      *
 214      * @param node pointer to the node which is updated
 215      * @param from_left variable which says that the request arrived
 216      * from the left
 217      * @param sum_from_below Sum of left and right children below
 218      * @param level level in the tree the calling node is located
 219      * @param stack_dist stack distance of the node below
 220      * @param discard_node whether the calling node was discarded or not
 221      * @return The stack distance of the current address.
 222      *
 223      */
 224     uint64_t updateSum(Node* node,
 225                        bool from_left, uint64_t sum_from_below, uint64_t level,
 226                        uint64_t stack_dist, bool discard_node);
 227
 228     /**
 229      * Updates the leaf nodes and nodes above. This function is
 230      * called by the calcStackDistAndUpdate.
 231      *
 232      * @param node pointer to the node which is updated
 233      * @param is_new_leaf is true if this is a newly added node
 234      * @return The stack distance of the current address.
 235      *
 236      */
 237     uint64_t updateSumsLeavesToRoot(Node* node, bool is_new_leaf);
 238
 239     /**
 240      * updateTree is a tree balancing operation, which maintains the
 241      * binary tree structure.
 242      * This method is called whenever index%2 == 0 (i.e. every
 243      * alternate cycle) The two main operation are :
 244      * OP1. Moving the root node one layer up if index counter
 245      *       crosses power of 2
 246      * OP2. Addition of intermediate nodes as and when required
 247      *      and linking them to their parents in the layer above.
 248      */
 249     void updateTree();
 250
 251     /**
 252      * This method is used for verification purposes
 253      * It recursively traverses upwards from the given node till
 254      * the root to check if the ultimate parent node (root-node) points
 255      * to null.
 256      *
 257      * @param node pointer to the node whose sanity is being checked
 258      * @param level the level at which this node is located in the tree
 259      *
 260      */
 261     void sanityCheckTree(const Node* node, uint64_t level = 0) const;
 262
 263     /**
 264      * Return the counter for address accesses (unique and
 265      * non-unique). This is further used to dump stats at
 266      * regular intervals.
 267      *
 268      * @return The stack distance of the current address.
 269      */
 270     uint64_t getIndex() const { return index; }
 271
 272     /**
 273      * Query depth of the tree (tree[0] represents leaf layer while
 274      * tree[treeDepth] represents the root layer, all layers in
 275      * between contain intermediate nodes)
 276      *
 277      * @return Tree depth
 278      */
 279     uint64_t getTreeDepth() const { return tree.size() - 1; }
 280
 281     /**
 282      * Print the last n items on the stack.
 283      * This method prints top n entries in the tree based implementation as
 284      * well as dummy stack.
 285      * @param n Number of entries to print
 286      */
 287     void printStack(int n = 5) const;
 288
 289     /**
 290      * This is an alternative implementation of the stack-distance
 291      * in a naive way. It uses simple STL vector to represent the stack.
 292      * It can be used in parallel for debugging purposes.
 293      * It is 10x slower than the tree based implemenation.
 294      *
 295      * @param r_address The current address to process
 296      * @param update_stack Flag to indicate if stack should be updated
 297      * @return  Stack distance which is calculated by this alternative
 298      * implementation
 299      *
 300      */
 301     uint64_t verifyStackDist(const Addr r_address,
 302                              bool update_stack = false);
 303
 304   public:
 305     StackDistCalc(bool verify_stack = false);
 306
 307     ~StackDistCalc();
 308
 309     /**
 310      * A convenient way of refering to infinity.
 311      */
 312     static constexpr uint64_t Infinity = std::numeric_limits<uint64_t>::max();
 313
 314
 315     /**
 316      * Process the given address. If Mark is true then set the
 317      * mark flag of the leaf node.
 318      * This function returns the stack distance of the incoming
 319      * address and the previous status of the mark flag.
 320      *
 321      * @param r_address The current address to process
 322      * @param mark set the mark flag for the address.
 323      * @return The stack distance of the current address and the mark flag.
 324      */
 325     std::pair<uint64_t, bool> calcStackDist(const Addr r_address,
 326                                             bool mark = false);
 327
 328     /**
 329      * Process the given address:
 330      *  - Lookup the tree for the given address
 331      *  - delete old node if found in tree
 332      *  - add a new node (if addNewNode flag is set)
 333      * This function returns the stack distance of the incoming
 334      * address and the status of the mark flag.
 335      *
 336      * @param r_address The current address to process
 337      * @param addNewNode If true, a new node is added to the tree
 338      * @return The stack distance of the current address and the mark flag.
 339      */
 340     std::pair<uint64_t, bool> calcStackDistAndUpdate(const Addr r_address,
 341                                                      bool addNewNode = true);
 342
 343   private:
 344
 345     /**
 346      * Node which takes form of Leaf, INode or Root
 347      */
 348     struct Node{
 349         // Sum of the left children
 350         uint64_t sumLeft;
 351
 352         // Sum of the right children
 353         uint64_t sumRight;
 354
 355         // Flag to indicate that sumLeft has gone from non-zero value to 0
 356         bool discardLeft;
 357
 358         // Flag to indicate that sumRight has gone from non-zero value to 0
 359         bool discardRight;
 360
 361         // Index of the current element in the Map
 362         uint64_t nodeIndex;
 363
 364         // Pointer to the parent
 365         Node* parent;
 366
 367         // Flag to mark the node as the right/left child
 368         bool isLeftNode;
 369
 370         /**
 371          * Flag to indicate if this address is marked. Used in case
 372          * where stack distance of a touched address is required.
 373          */
 374         bool isMarked;
 375
 376         /**
 377          * The discard flags are false by default they become true if
 378          * the node is reached again in a future lookup.
 379          */
 380         Node() : sumLeft(0), sumRight(0), discardLeft(false),
 381                  discardRight(false), nodeIndex(0),
 382                  parent(nullptr), isLeftNode(true), isMarked(false)
 383         { }
 384     };
 385
 386     /**
 387      * Internal counter for address accesses (unique and non-unique)
 388      * This counter increments everytime the calcStackDist() method is
 389      * called. This counter is used as a key for the hash- map at the
 390      * leaf layer. Practically at every call to the calculator this
 391      * counter is incremented and a new leaf node is added in the tree
 392      * at the leaf layer using this counter value as the key.
 393      */
 394     uint64_t index;
 395
 396     // Binary tree of partial sums
 397     TreeType tree;
 398
 399     // Hash map which returns last seen index of each address
 400     AddressIndexMap aiMap;
 401
 402     // Keeps count of number of the next unique index for each
 403     // level in the tree
 404     std::vector<uint64_t> nextIndex;
 405
 406     // Dummy Stack for verification
 407     std::vector<uint64_t> stack;
 408
 409     // Flag to enable verification of stack. (Slows down the simulation)
 410     const bool verifyStack;
 411 };
 412
 413
 414 #endif //__STACK_DIST_CALC_HH__