tree_plru_rp.cc revision 13221:48bce2835200 
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 <memory>
40
41#include "base/intmath.hh"
42#include "params/TreePLRURP.hh"
43
44/**
45 * Get the index of the parent of the given indexed subtree.
46 *
47 * @param Index of the queried tree.
48 * @return The index of the parent tree.
49 */
50static uint64_t
51parentIndex(const uint64_t index)
52{
53    return std::floor((index-1)/2);
54}
55
56/**
57 * Get index of the subtree on the left of the given indexed tree.
58 *
59 * @param index The index of the queried tree.
60 * @return The index of the subtree to the left of the queried tree.
61 */
62static uint64_t
63leftSubtreeIndex(const uint64_t index)
64{
65    return 2*index + 1;
66}
67
68/**
69 * Get index of the subtree on the right of the given indexed tree.
70 *
71 * @param index The index of the queried tree.
72 * @return The index of the subtree to the right of the queried tree.
73 */
74static uint64_t
75rightSubtreeIndex(const uint64_t index)
76{
77    return 2*index + 2;
78}
79
80/**
81 * Find out if the subtree at index corresponds to the right or left subtree
82 * of its parent tree.
83 *
84 * @param index The index of the subtree.
85 * @return True if it is a right subtree, false otherwise.
86 */
87static bool
88isRightSubtree(const uint64_t index)
89{
90    return index%2 == 0;
91}
92
93TreePLRURP::TreePLRUReplData::TreePLRUReplData(
94    const uint64_t index, std::shared_ptr<PLRUTree> tree)
95    : index(index), tree(tree)
96{
97}
98
99TreePLRURP::TreePLRURP(const Params *p)
100    : BaseReplacementPolicy(p), numLeaves(p->num_leaves), count(0),
101      treeInstance(nullptr)
102{
103    fatal_if(!isPowerOf2(numLeaves),
104             "Number of leaves must be non-zero and a power of 2");
105}
106
107void
108TreePLRURP::invalidate(
109    const std::shared_ptr<ReplacementData>& replacement_data) const
110{
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();
115
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;
119
120    // Parse and update tree to make it point to the new LRU
121    do {
122        // Store whether we are coming from a left or right node
123        const bool right = isRightSubtree(tree_index);
124
125        // Go to the parent tree node
126        tree_index = parentIndex(tree_index);
127
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);
131}
132
133void
134TreePLRURP::touch(const std::shared_ptr<ReplacementData>& replacement_data)
135const
136{
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();
141
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;
145
146    // Parse and update tree to make every bit point away from the new MRU
147    do {
148        // Store whether we are coming from a left or right node
149        const bool right = isRightSubtree(tree_index);
150
151        // Go to the parent tree node
152        tree_index = parentIndex(tree_index);
153
154        // Update node to not point to the touched leaf
155        tree->at(tree_index) = !right;
156    } while (tree_index != 0);
157}
158
159void
160TreePLRURP::reset(const std::shared_ptr<ReplacementData>& replacement_data)
161const
162{
163    // A reset has the same functionality of a touch
164    touch(replacement_data);
165}
166
167ReplaceableEntry*
168TreePLRURP::getVictim(const ReplacementCandidates& candidates) const
169{
170    // There must be at least one replacement candidate
171    assert(candidates.size() > 0);
172
173    // Get tree
174    const PLRUTree* tree = std::static_pointer_cast<TreePLRUReplData>(
175            candidates[0]->replacementData)->tree.get();
176
177    // Index of the tree entry we are currently checking. Start with root.
178    uint64_t tree_index = 0;
179
180    // Parse tree
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);
185        } else {
186            tree_index = leftSubtreeIndex(tree_index);
187        }
188    }
189
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)];
193}
194
195std::shared_ptr<ReplacementData>
196TreePLRURP::instantiateEntry()
197{
198    // Generate a tree instance every numLeaves created
199    if (count % numLeaves == 0) {
200        treeInstance = new PLRUTree(numLeaves - 1, false);
201    }
202
203    // Create replacement data using current tree instance
204    TreePLRUReplData* treePLRUReplData = new TreePLRUReplData(
205        (count % numLeaves) + numLeaves - 1,
206        std::shared_ptr<PLRUTree>(treeInstance));
207
208    // Update instance counter
209    count++;
210
211    return std::shared_ptr<ReplacementData>(treePLRUReplData);
212}
213
214TreePLRURP*
215TreePLRURPParams::create()
216{
217    return new TreePLRURP(this);
218}
219