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