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Diffstat (limited to 'src/mem/ruby/structures/PseudoLRUPolicy.hh')
| -rw-r--r-- | src/mem/ruby/structures/PseudoLRUPolicy.hh | 137 |
1 files changed, 137 insertions, 0 deletions
diff --git a/src/mem/ruby/structures/PseudoLRUPolicy.hh b/src/mem/ruby/structures/PseudoLRUPolicy.hh new file mode 100644 index 000000000..e464bbeac --- /dev/null +++ b/src/mem/ruby/structures/PseudoLRUPolicy.hh @@ -0,0 +1,137 @@ +/* + * Copyright (c) 2007 Mark D. Hill and David A. Wood + * 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. + */ + +#ifndef __MEM_RUBY_SYSTEM_PSEUDOLRUPOLICY_HH__ +#define __MEM_RUBY_SYSTEM_PSEUDOLRUPOLICY_HH__ + +#include "mem/ruby/structures/AbstractReplacementPolicy.hh" + +/** + * Implementation of tree-based pseudo-LRU replacement + * + * Works for any associativity between 1 and 128. + * + * Also implements associativities that are not a power of 2 by + * ignoring paths that lead to a larger index (i.e. truncating the + * tree). Note that when this occurs, the algorithm becomes less + * fair, as it will favor indicies in the larger (by index) half of + * the associative set. This is most unfair when the nearest power of + * 2 is one below the associativy, and most fair when it is one above. + */ + +class PseudoLRUPolicy : public AbstractReplacementPolicy +{ + public: + PseudoLRUPolicy(Index num_sets, Index assoc); + ~PseudoLRUPolicy(); + + void touch(Index set, Index way, Tick time); + Index getVictim(Index set) const; + + private: + unsigned int m_effective_assoc; /** nearest (to ceiling) power of 2 */ + unsigned int m_num_levels; /** number of levels in the tree */ + uint64* m_trees; /** bit representation of the + * trees, one for each set */ +}; + +inline +PseudoLRUPolicy::PseudoLRUPolicy(Index num_sets, Index assoc) + : AbstractReplacementPolicy(num_sets, assoc) +{ + // associativity cannot exceed capacity of tree representation + assert(num_sets > 0 && assoc > 1 && assoc <= (Index) sizeof(uint64)*4); + + m_trees = NULL; + m_num_levels = 0; + + m_effective_assoc = 1; + while (m_effective_assoc < assoc) { + // effective associativity is ceiling power of 2 + m_effective_assoc <<= 1; + } + assoc = m_effective_assoc; + while (true) { + assoc /= 2; + if(!assoc) break; + m_num_levels++; + } + assert(m_num_levels < sizeof(unsigned int)*4); + m_trees = new uint64[m_num_sets]; + for (unsigned i = 0; i < m_num_sets; i++) { + m_trees[i] = 0; + } +} + +inline +PseudoLRUPolicy::~PseudoLRUPolicy() +{ + if (m_trees != NULL) + delete[] m_trees; +} + +inline void +PseudoLRUPolicy::touch(Index set, Index index, Tick time) +{ + assert(index >= 0 && index < m_assoc); + assert(set >= 0 && set < m_num_sets); + + int tree_index = 0; + int node_val; + for (int i = m_num_levels - 1; i >= 0; i--) { + node_val = (index >> i)&1; + if (node_val) + m_trees[set] |= node_val << tree_index; + else + m_trees[set] &= ~(1 << tree_index); + tree_index = node_val ? (tree_index*2)+2 : (tree_index*2)+1; + } + m_last_ref_ptr[set][index] = time; +} + +inline Index +PseudoLRUPolicy::getVictim(Index set) const +{ + // assert(m_assoc != 0); + Index index = 0; + + int tree_index = 0; + int node_val; + for (unsigned i = 0; i < m_num_levels; i++){ + node_val = (m_trees[set] >> tree_index) & 1; + index += node_val ? 0 : (m_effective_assoc >> (i + 1)); + tree_index = node_val ? (tree_index * 2) + 1 : (tree_index * 2) + 2; + } + assert(index >= 0 && index < m_effective_assoc); + + /* return either the found index or the max possible index */ + /* NOTE: this is not a fair replacement when assoc is not a power of 2 */ + return (index > (m_assoc - 1)) ? m_assoc - 1 : index; +} + +#endif // __MEM_RUBY_SYSTEM_PSEUDOLRUPOLICY_HH__ |