1/**
2 * Copyright (c) 2018 Inria
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions are
7 * met: redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer;
9 * redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution;
12 * neither the name of the copyright holders nor the names of its
13 * contributors may be used to endorse or promote products derived from
14 * this software without specific prior written permission.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
20 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
26 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 *
28 * Authors: Daniel Carvalho
29 */
30
31/**
32 * @file
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.
35 */
36
37#include "mem/cache/replacement_policies/tree_plru_rp.hh"
38
39#include <cmath>
40
41#include "base/intmath.hh"
42#include "base/logging.hh"
43#include "params/TreePLRURP.hh"
44
45/**
46 * Get the index of the parent of the given indexed subtree.
47 *
48 * @param Index of the queried tree.
49 * @return The index of the parent tree.
50 */
51static uint64_t
52parentIndex(const uint64_t index)
53{
54    return std::floor((index-1)/2);
55}
56
57/**
58 * Get index of the subtree on the left of the given indexed tree.
59 *
60 * @param index The index of the queried tree.
61 * @return The index of the subtree to the left of the queried tree.
62 */
63static uint64_t
64leftSubtreeIndex(const uint64_t index)
65{
66    return 2*index + 1;
67}
68
69/**
70 * Get index of the subtree on the right of the given indexed tree.
71 *
72 * @param index The index of the queried tree.
73 * @return The index of the subtree to the right of the queried tree.
74 */
75static uint64_t
76rightSubtreeIndex(const uint64_t index)
77{
78    return 2*index + 2;
79}
80
81/**
82 * Find out if the subtree at index corresponds to the right or left subtree
83 * of its parent tree.
84 *
85 * @param index The index of the subtree.
86 * @return True if it is a right subtree, false otherwise.
87 */
88static bool
89isRightSubtree(const uint64_t index)
90{
91    return index%2 == 0;
92}
93
94TreePLRURP::TreePLRUReplData::TreePLRUReplData(
95    const uint64_t index, std::shared_ptr<PLRUTree> tree)
96    : index(index), tree(tree)
97{
98}
99
100TreePLRURP::TreePLRURP(const Params *p)
101    : BaseReplacementPolicy(p), numLeaves(p->num_leaves), count(0),
102      treeInstance(nullptr)
103{
104    fatal_if(!isPowerOf2(numLeaves),
105             "Number of leaves must be non-zero and a power of 2");
106}
107
108void
109TreePLRURP::invalidate(
110    const std::shared_ptr<ReplacementData>& replacement_data) const
111{
112    // Cast replacement data
113    std::shared_ptr<TreePLRUReplData> treePLRU_replacement_data =
114        std::static_pointer_cast<TreePLRUReplData>(replacement_data);
115    PLRUTree* tree = treePLRU_replacement_data->tree.get();
116
117    // Index of the tree entry we are currently checking
118    // Make this entry the new LRU entry
119    uint64_t tree_index = treePLRU_replacement_data->index;
120
121    // Parse and update tree to make it point to the new LRU
122    do {
123        // Store whether we are coming from a left or right node
124        const bool right = isRightSubtree(tree_index);
125
126        // Go to the parent tree node
127        tree_index = parentIndex(tree_index);
128
129        // Update parent node to make it point to the node we just came from
130        tree->at(tree_index) = right;
131    } while (tree_index != 0);
132}
133
134void
135TreePLRURP::touch(const std::shared_ptr<ReplacementData>& replacement_data)
136const
137{
138    // Cast replacement data
139    std::shared_ptr<TreePLRUReplData> treePLRU_replacement_data =
140        std::static_pointer_cast<TreePLRUReplData>(replacement_data);
141    PLRUTree* tree = treePLRU_replacement_data->tree.get();
142
143    // Index of the tree entry we are currently checking
144    // Make this entry the MRU entry
145    uint64_t tree_index = treePLRU_replacement_data->index;
146
147    // Parse and update tree to make every bit point away from the new MRU
148    do {
149        // Store whether we are coming from a left or right node
150        const bool right = isRightSubtree(tree_index);
151
152        // Go to the parent tree node
153        tree_index = parentIndex(tree_index);
154
155        // Update node to not point to the touched leaf
156        tree->at(tree_index) = !right;
157    } while (tree_index != 0);
158}
159
160void
161TreePLRURP::reset(const std::shared_ptr<ReplacementData>& replacement_data)
162const
163{
164    // A reset has the same functionality of a touch
165    touch(replacement_data);
166}
167
168ReplaceableEntry*
169TreePLRURP::getVictim(const ReplacementCandidates& candidates) const
170{
171    // There must be at least one replacement candidate
172    assert(candidates.size() > 0);
173
174    // Get tree
175    const PLRUTree* tree = std::static_pointer_cast<TreePLRUReplData>(
176            candidates[0]->replacementData)->tree.get();
177
178    // Index of the tree entry we are currently checking. Start with root.
179    uint64_t tree_index = 0;
180
181    // Parse tree
182    while (tree_index < tree->size()) {
183        // Go to the next tree entry
184        if (tree->at(tree_index)) {
185            tree_index = rightSubtreeIndex(tree_index);
186        } else {
187            tree_index = leftSubtreeIndex(tree_index);
188        }
189    }
190
191    // The tree index is currently at the leaf of the victim displaced by the
192    // number of non-leaf nodes
193    return candidates[tree_index - (numLeaves - 1)];
194}
195
196std::shared_ptr<ReplacementData>
197TreePLRURP::instantiateEntry()
198{
199    // Generate a tree instance every numLeaves created
200    if (count % numLeaves == 0) {
201        treeInstance = new PLRUTree(numLeaves - 1, false);
202    }
203
204    // Create replacement data using current tree instance
205    TreePLRUReplData* treePLRUReplData = new TreePLRUReplData(
206        (count % numLeaves) + numLeaves - 1,
207        std::shared_ptr<PLRUTree>(treeInstance));
208
209    // Update instance counter
210    count++;
211
212    return std::shared_ptr<ReplacementData>(treePLRUReplData);
213}
214
215TreePLRURP*
216TreePLRURPParams::create()
217{
218    return new TreePLRURP(this);
219}
220