From 04d236e5687ba11d71ced0a37044fdd55aa5bb42 Mon Sep 17 00:00:00 2001 From: "Daniel R. Carvalho" Date: Fri, 23 Mar 2018 16:08:51 +0100 Subject: [PATCH] mem-cache: Create Second-Chance replacement policy Implementation of a Second-Chance replacement policy. Similar to FIFO, but every block is given a second chance if it has been touched. Change-Id: Id4d52b698d0045a4914a4d848fdf9c3c00a28508 Reviewed-on: https://gem5-review.googlesource.com/9441 Reviewed-by: Nikos Nikoleris Maintainer: Nikos Nikoleris --- .../ReplacementPolicies.py | 5 + src/mem/cache/replacement_policies/SConscript | 1 + src/mem/cache/replacement_policies/fifo_rp.hh | 1 + .../replacement_policies/second_chance_rp.cc | 134 ++++++++++++++++++ .../replacement_policies/second_chance_rp.hh | 133 +++++++++++++++++ 5 files changed, 274 insertions(+) create mode 100644 src/mem/cache/replacement_policies/second_chance_rp.cc create mode 100644 src/mem/cache/replacement_policies/second_chance_rp.hh diff --git a/src/mem/cache/replacement_policies/ReplacementPolicies.py b/src/mem/cache/replacement_policies/ReplacementPolicies.py index 381f386ed..5737fa450 100644 --- a/src/mem/cache/replacement_policies/ReplacementPolicies.py +++ b/src/mem/cache/replacement_policies/ReplacementPolicies.py @@ -40,6 +40,11 @@ class FIFORP(BaseReplacementPolicy): cxx_class = 'FIFORP' cxx_header = "mem/cache/replacement_policies/fifo_rp.hh" +class SecondChanceRP(FIFORP): + type = 'SecondChanceRP' + cxx_class = 'SecondChanceRP' + cxx_header = "mem/cache/replacement_policies/second_chance_rp.hh" + class LFURP(BaseReplacementPolicy): type = 'LFURP' cxx_class = 'LFURP' diff --git a/src/mem/cache/replacement_policies/SConscript b/src/mem/cache/replacement_policies/SConscript index 74022feda..d6a354a87 100644 --- a/src/mem/cache/replacement_policies/SConscript +++ b/src/mem/cache/replacement_policies/SConscript @@ -39,3 +39,4 @@ Source('lfu_rp.cc') Source('lru_rp.cc') Source('mru_rp.cc') Source('random_rp.cc') +Source('second_chance_rp.cc') diff --git a/src/mem/cache/replacement_policies/fifo_rp.hh b/src/mem/cache/replacement_policies/fifo_rp.hh index a686b449b..34067d50f 100644 --- a/src/mem/cache/replacement_policies/fifo_rp.hh +++ b/src/mem/cache/replacement_policies/fifo_rp.hh @@ -43,6 +43,7 @@ class FIFORP : public BaseReplacementPolicy { + protected: /** FIFO-specific implementation of replacement data. */ struct FIFOReplData : ReplacementData { diff --git a/src/mem/cache/replacement_policies/second_chance_rp.cc b/src/mem/cache/replacement_policies/second_chance_rp.cc new file mode 100644 index 000000000..2560a9846 --- /dev/null +++ b/src/mem/cache/replacement_policies/second_chance_rp.cc @@ -0,0 +1,134 @@ +/** + * Copyright (c) 2018 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. + * + * Authors: Daniel Carvalho + */ + +#include "mem/cache/replacement_policies/second_chance_rp.hh" + +SecondChanceRP::SecondChanceRP(const Params *p) + : FIFORP(p) +{ +} + +void +SecondChanceRP::useSecondChance( + const std::shared_ptr& replacement_data) const +{ + // Reset FIFO data + FIFORP::reset(replacement_data); + + // Use second chance + replacement_data->hasSecondChance = false; +} + +void +SecondChanceRP::invalidate( + const std::shared_ptr& replacement_data) const +{ + FIFORP::invalidate(replacement_data); + + // Do not give a second chance to invalid entries + std::static_pointer_cast( + replacement_data)->hasSecondChance = false; +} + +void +SecondChanceRP::touch(const std::shared_ptr& replacement_data) const +{ + FIFORP::touch(replacement_data); + + // Whenever an entry is touched, it is given a second chance + std::static_pointer_cast( + replacement_data)->hasSecondChance = true; +} + +void +SecondChanceRP::reset(const std::shared_ptr& replacement_data) const +{ + FIFORP::reset(replacement_data); + + // Entries are inserted with a second chance + std::static_pointer_cast( + replacement_data)->hasSecondChance = true; +} + +ReplaceableEntry* +SecondChanceRP::getVictim(const ReplacementCandidates& candidates) const +{ + // There must be at least one replacement candidate + assert(candidates.size() > 0); + + // Search for invalid entries, as they have the eviction priority + for (const auto& candidate : candidates) { + // Cast candidate's replacement data + std::shared_ptr candidate_replacement_data = + std::static_pointer_cast( + candidate->replacementData); + + // Stop iteration if found an invalid entry + if ((candidate_replacement_data->tickInserted == Tick(0)) && + !candidate_replacement_data->hasSecondChance) { + return candidate; + } + } + + // Visit all candidates to find victim + ReplaceableEntry* victim = candidates[0]; + bool search_victim = true; + while (search_victim) { + // Do a FIFO victim search + victim = FIFORP::getVictim(candidates); + + // Cast victim's replacement data for code readability + std::shared_ptr victim_replacement_data = + std::static_pointer_cast( + victim->replacementData); + + // If victim has a second chance, use it and repeat search + if (victim_replacement_data->hasSecondChance) { + useSecondChance(victim_replacement_data); + } else { + // Found victim + search_victim = false; + } + } + + return victim; +} + +std::shared_ptr +SecondChanceRP::instantiateEntry() +{ + return std::shared_ptr(new SecondChanceReplData()); +} + +SecondChanceRP* +SecondChanceRPParams::create() +{ + return new SecondChanceRP(this); +} diff --git a/src/mem/cache/replacement_policies/second_chance_rp.hh b/src/mem/cache/replacement_policies/second_chance_rp.hh new file mode 100644 index 000000000..5522d5e7f --- /dev/null +++ b/src/mem/cache/replacement_policies/second_chance_rp.hh @@ -0,0 +1,133 @@ +/** + * Copyright (c) 2018 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. + * + * Authors: Daniel Carvalho + */ + +/** + * @file + * Declaration of a Second-Chance replacement policy. + * The victim is chosen using the timestamp. The oldest entry is chosen + * to be evicted, if it hasn't been touched since its insertion. If it + * has been touched, it is given a second chance and re-inserted at the + * end of the queue. + */ + +#ifndef __MEM_CACHE_REPLACEMENT_POLICIES_SECOND_CHANCE_RP_HH__ +#define __MEM_CACHE_REPLACEMENT_POLICIES_SECOND_CHANCE_RP_HH__ + +#include "mem/cache/replacement_policies/fifo_rp.hh" +#include "params/SecondChanceRP.hh" + +class SecondChanceRP : public FIFORP +{ + protected: + /** Second-Chance-specific implementation of replacement data. */ + struct SecondChanceReplData : public FIFOReplData + { + /** + * This is different from isTouched because isTouched accounts only + * for insertion, while this bit is reset every new re-insertion. + * @sa SecondChanceRP. + */ + bool hasSecondChance; + + /** + * Default constructor. + */ + SecondChanceReplData() : FIFOReplData(), hasSecondChance(false) {} + }; + + /** + * Use replacement data's second chance. + * + * @param replacement_data Entry that will use its second chance. + */ + void useSecondChance( + const std::shared_ptr& replacement_data) const; + + public: + /** Convenience typedef. */ + typedef SecondChanceRPParams Params; + + /** + * Construct and initiliaze this replacement policy. + */ + SecondChanceRP(const Params *p); + + /** + * Destructor. + */ + ~SecondChanceRP() {} + + /** + * Invalidate replacement data to set it as the next probable victim. + * Invalid entries do not have a second chance, and their last touch tick + * is set as the oldest possible. + * + * @param replacement_data Replacement data to be invalidated. + */ + void invalidate(const std::shared_ptr& replacement_data) + const override; + + /** + * Touch an entry to update its re-insertion tick and second chance bit. + * + * @param replacement_data Replacement data to be touched. + */ + void touch(const std::shared_ptr& replacement_data) const + override; + + /** + * Reset replacement data. Used when an entry is inserted or re-inserted + * in the queue. + * Sets its insertion tick and second chance bit. + * + * @param replacement_data Replacement data to be reset. + */ + void reset(const std::shared_ptr& replacement_data) const + override; + + /** + * Find replacement victim using insertion timestamps and second chance + * bit. + * + * @param cands Replacement candidates, selected by indexing policy. + * @return Replacement entry to be replaced. + */ + ReplaceableEntry* getVictim(const ReplacementCandidates& candidates) const + override; + + /** + * Instantiate a replacement data entry. + * + * @return A shared pointer to the new replacement data. + */ + std::shared_ptr instantiateEntry() override; +}; + +#endif // __MEM_CACHE_REPLACEMENT_POLICIES_SECOND_CHANCE_RP_HH__ -- 2.30.2