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/**
* Copyright (c) 2018-2020 Inria
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
* redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution;
* neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/**
* @file
* Definitions of a Tree-PLRU replacement policy, along with some helper
* tree indexing functions, which map an index to the tree 2D-array.
*/
#include "mem/cache/replacement_policies/tree_plru_rp.hh"
#include <cmath>
#include "base/intmath.hh"
#include "base/logging.hh"
#include "params/TreePLRURP.hh"
namespace gem5
{
GEM5_DEPRECATED_NAMESPACE(ReplacementPolicy, replacement_policy);
namespace replacement_policy
{
/**
* Get the index of the parent of the given indexed subtree.
*
* @param Index of the queried tree.
* @return The index of the parent tree.
*/
static uint64_t
parentIndex(const uint64_t index)
{
return std::floor((index-1)/2);
}
/**
* Get index of the subtree on the left of the given indexed tree.
*
* @param index The index of the queried tree.
* @return The index of the subtree to the left of the queried tree.
*/
static uint64_t
leftSubtreeIndex(const uint64_t index)
{
return 2*index + 1;
}
/**
* Get index of the subtree on the right of the given indexed tree.
*
* @param index The index of the queried tree.
* @return The index of the subtree to the right of the queried tree.
*/
static uint64_t
rightSubtreeIndex(const uint64_t index)
{
return 2*index + 2;
}
/**
* Find out if the subtree at index corresponds to the right or left subtree
* of its parent tree.
*
* @param index The index of the subtree.
* @return True if it is a right subtree, false otherwise.
*/
static bool
isRightSubtree(const uint64_t index)
{
return index%2 == 0;
}
TreePLRU::TreePLRUReplData::TreePLRUReplData(
const uint64_t index, std::shared_ptr<PLRUTree> tree)
: index(index), tree(tree)
{
}
TreePLRU::TreePLRU(const Params &p)
: Base(p), numLeaves(p.num_leaves), count(0), treeInstance(nullptr)
{
fatal_if(!isPowerOf2(numLeaves),
"Number of leaves must be non-zero and a power of 2");
}
void
TreePLRU::invalidate(const std::shared_ptr<ReplacementData>& replacement_data)
{
// Cast replacement data
std::shared_ptr<TreePLRUReplData> treePLRU_replacement_data =
std::static_pointer_cast<TreePLRUReplData>(replacement_data);
PLRUTree* tree = treePLRU_replacement_data->tree.get();
// Index of the tree entry we are currently checking
// Make this entry the new LRU entry
uint64_t tree_index = treePLRU_replacement_data->index;
// Parse and update tree to make it point to the new LRU
do {
// Store whether we are coming from a left or right node
const bool right = isRightSubtree(tree_index);
// Go to the parent tree node
tree_index = parentIndex(tree_index);
// Update parent node to make it point to the node we just came from
tree->at(tree_index) = right;
} while (tree_index != 0);
}
void
TreePLRU::touch(const std::shared_ptr<ReplacementData>& replacement_data)
const
{
// Cast replacement data
std::shared_ptr<TreePLRUReplData> treePLRU_replacement_data =
std::static_pointer_cast<TreePLRUReplData>(replacement_data);
PLRUTree* tree = treePLRU_replacement_data->tree.get();
// Index of the tree entry we are currently checking
// Make this entry the MRU entry
uint64_t tree_index = treePLRU_replacement_data->index;
// Parse and update tree to make every bit point away from the new MRU
do {
// Store whether we are coming from a left or right node
const bool right = isRightSubtree(tree_index);
// Go to the parent tree node
tree_index = parentIndex(tree_index);
// Update node to not point to the touched leaf
tree->at(tree_index) = !right;
} while (tree_index != 0);
}
void
TreePLRU::reset(const std::shared_ptr<ReplacementData>& replacement_data)
const
{
// A reset has the same functionality of a touch
touch(replacement_data);
}
ReplaceableEntry*
TreePLRU::getVictim(const ReplacementCandidates& candidates) const
{
// There must be at least one replacement candidate
assert(candidates.size() > 0);
// Get tree
const PLRUTree* tree = std::static_pointer_cast<TreePLRUReplData>(
candidates[0]->replacementData)->tree.get();
// Index of the tree entry we are currently checking. Start with root.
uint64_t tree_index = 0;
// Parse tree
while (tree_index < tree->size()) {
// Go to the next tree entry
if (tree->at(tree_index)) {
tree_index = rightSubtreeIndex(tree_index);
} else {
tree_index = leftSubtreeIndex(tree_index);
}
}
// The tree index is currently at the leaf of the victim displaced by the
// number of non-leaf nodes
return candidates[tree_index - (numLeaves - 1)];
}
std::shared_ptr<ReplacementData>
TreePLRU::instantiateEntry()
{
// Generate a tree instance every numLeaves created
if (count % numLeaves == 0) {
treeInstance = new PLRUTree(numLeaves - 1, false);
}
// Create replacement data using current tree instance
TreePLRUReplData* treePLRUReplData = new TreePLRUReplData(
(count % numLeaves) + numLeaves - 1,
std::shared_ptr<PLRUTree>(treeInstance));
// Update instance counter
count++;
return std::shared_ptr<ReplacementData>(treePLRUReplData);
}
} // namespace replacement_policy
} // namespace gem5