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28 * Authors: Daniel Carvalho
33 * Definitions of a Tree-PLRU replacement policy, along with some helper
34 * tree indexing functions, which map an index to the tree 2D-array.
37 #include "mem/cache/replacement_policies/tree_plru_rp.hh"
41 #include "base/intmath.hh"
42 #include "params/TreePLRURP.hh"
45 * Get the index of the parent of the given indexed subtree.
47 * @param Index of the queried tree.
48 * @return The index of the parent tree.
51 parentIndex(const uint64_t index
)
53 return std::floor((index
-1)/2);
57 * Get index of the subtree on the left of the given indexed tree.
59 * @param index The index of the queried tree.
60 * @return The index of the subtree to the left of the queried tree.
63 leftSubtreeIndex(const uint64_t index
)
69 * Get index of the subtree on the right of the given indexed tree.
71 * @param index The index of the queried tree.
72 * @return The index of the subtree to the right of the queried tree.
75 rightSubtreeIndex(const uint64_t index
)
81 * Find out if the subtree at index corresponds to the right or left subtree
84 * @param index The index of the subtree.
85 * @return True if it is a right subtree, false otherwise.
88 isRightSubtree(const uint64_t index
)
93 TreePLRURP::TreePLRUReplData::TreePLRUReplData(
94 const uint64_t index
, std::shared_ptr
<PLRUTree
> tree
)
95 : index(index
), tree(tree
)
99 TreePLRURP::TreePLRURP(const Params
*p
)
100 : BaseReplacementPolicy(p
), numLeaves(p
->num_leaves
), count(0),
101 treeInstance(nullptr)
103 fatal_if(!isPowerOf2(numLeaves
),
104 "Number of leaves must be non-zero and a power of 2");
108 TreePLRURP::invalidate(
109 const std::shared_ptr
<ReplacementData
>& replacement_data
) const
111 // Cast replacement data
112 std::shared_ptr
<TreePLRUReplData
> treePLRU_replacement_data
=
113 std::static_pointer_cast
<TreePLRUReplData
>(replacement_data
);
114 PLRUTree
* tree
= treePLRU_replacement_data
->tree
.get();
116 // Index of the tree entry we are currently checking
117 // Make this entry the new LRU entry
118 uint64_t tree_index
= treePLRU_replacement_data
->index
;
120 // Parse and update tree to make it point to the new LRU
122 // Store whether we are coming from a left or right node
123 const bool right
= isRightSubtree(tree_index
);
125 // Go to the parent tree node
126 tree_index
= parentIndex(tree_index
);
128 // Update parent node to make it point to the node we just came from
129 tree
->at(tree_index
) = right
;
130 } while (tree_index
!= 0);
134 TreePLRURP::touch(const std::shared_ptr
<ReplacementData
>& replacement_data
)
137 // Cast replacement data
138 std::shared_ptr
<TreePLRUReplData
> treePLRU_replacement_data
=
139 std::static_pointer_cast
<TreePLRUReplData
>(replacement_data
);
140 PLRUTree
* tree
= treePLRU_replacement_data
->tree
.get();
142 // Index of the tree entry we are currently checking
143 // Make this entry the MRU entry
144 uint64_t tree_index
= treePLRU_replacement_data
->index
;
146 // Parse and update tree to make every bit point away from the new MRU
148 // Store whether we are coming from a left or right node
149 const bool right
= isRightSubtree(tree_index
);
151 // Go to the parent tree node
152 tree_index
= parentIndex(tree_index
);
154 // Update node to not point to the touched leaf
155 tree
->at(tree_index
) = !right
;
156 } while (tree_index
!= 0);
160 TreePLRURP::reset(const std::shared_ptr
<ReplacementData
>& replacement_data
)
163 // A reset has the same functionality of a touch
164 touch(replacement_data
);
168 TreePLRURP::getVictim(const ReplacementCandidates
& candidates
) const
170 // There must be at least one replacement candidate
171 assert(candidates
.size() > 0);
174 const PLRUTree
* tree
= std::static_pointer_cast
<TreePLRUReplData
>(
175 candidates
[0]->replacementData
)->tree
.get();
177 // Index of the tree entry we are currently checking. Start with root.
178 uint64_t tree_index
= 0;
181 while (tree_index
< tree
->size()) {
182 // Go to the next tree entry
183 if (tree
->at(tree_index
)) {
184 tree_index
= rightSubtreeIndex(tree_index
);
186 tree_index
= leftSubtreeIndex(tree_index
);
190 // The tree index is currently at the leaf of the victim displaced by the
191 // number of non-leaf nodes
192 return candidates
[tree_index
- (numLeaves
- 1)];
195 std::shared_ptr
<ReplacementData
>
196 TreePLRURP::instantiateEntry()
198 // Generate a tree instance every numLeaves created
199 if (count
% numLeaves
== 0) {
200 treeInstance
= new PLRUTree(numLeaves
- 1, false);
203 // Create replacement data using current tree instance
204 TreePLRUReplData
* treePLRUReplData
= new TreePLRUReplData(
205 (count
% numLeaves
) + numLeaves
- 1,
206 std::shared_ptr
<PLRUTree
>(treeInstance
));
208 // Update instance counter
211 return std::shared_ptr
<ReplacementData
>(treePLRUReplData
);
215 TreePLRURPParams::create()
217 return new TreePLRURP(this);