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authorDaniel R. Carvalho <odanrc@yahoo.com.br>2018-02-19 15:13:11 +0100
committerDaniel Carvalho <odanrc@yahoo.com.br>2018-03-22 14:50:23 +0000
commitd207e9ccee411877fdeac80bb68a27900560f50f (patch)
tree120810cf72c52ed5df29436552e06f1fb11aa5ce /src/mem/cache/replacement_policies/lru_rp.hh
parent0473286ab1e9992a906eff380000bf90c82eeccb (diff)
downloadgem5-d207e9ccee411877fdeac80bb68a27900560f50f.tar.xz
mem-cache: Split array indexing and replacement policies.
Replacement policies (LRU, Random) are currently considered as array indexing methods, but have completely different functionalities: - Array indexers determine the possible locations for block allocation. This information is used to generate replacement candidates when conflicts happen. - Replacement policies determine which of the replacement candidates should be evicted to make room for new allocations. For this reason, they were split into different classes. Advantages: - Easier and more straightforward to implement other replacement policies (RRIP, LFU, ARC, ...) - Allow easier future implementation of cache organization schemes As now we can't assure the use of sets, the previous way to create a true LRU is not viable. Now a timestamp_bits parameter controls how many bits are dedicated for the timestamp, and a true LRU can be achieved through an infinite number of bits (although a few bits suffice in practice). Change-Id: I23750db121f1474d17831137e6ff618beb2b3eda Reviewed-on: https://gem5-review.googlesource.com/8501 Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com> Reviewed-by: Jason Lowe-Power <jason@lowepower.com> Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
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+/**
+ * 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 Least Recently Used replacement policy.
+ * The victim is chosen using the timestamp. The timestamp may be true or
+ * pseudo, depending on the quantity of bits allocated for that.
+ */
+
+#ifndef __MEM_CACHE_REPLACEMENT_POLICIES_LRU_RP_HH__
+#define __MEM_CACHE_REPLACEMENT_POLICIES_LRU_RP_HH__
+
+#include "mem/cache/replacement_policies/base.hh"
+#include "params/LRURP.hh"
+
+class LRURP : public BaseReplacementPolicy
+{
+ public:
+ /** Convenience typedef. */
+ typedef LRURPParams Params;
+
+ /**
+ * Construct and initiliaze this replacement policy.
+ */
+ LRURP(const Params *p);
+
+ /**
+ * Destructor.
+ */
+ ~LRURP() {}
+
+ /**
+ * Touch a block to update its last touch tick.
+ *
+ * @param blk Cache block to be touched.
+ */
+ void touch(CacheBlk *blk);
+
+ /**
+ * Reset replacement data for a block. Used when a block is inserted.
+ * Sets its last touch tick as the current tick.
+ *
+ * @param blk Cache block to be reset.
+ */
+ void reset(CacheBlk *blk);
+
+ /**
+ * Find replacement victim using LRU timestamps.
+ *
+ * @param candidates Replacement candidates, selected by indexing policy.
+ * @return Cache block to be replaced.
+ */
+ CacheBlk* getVictim(const ReplacementCandidates& candidates) override;
+};
+
+#endif // __MEM_CACHE_REPLACEMENT_POLICIES_LRU_RP_HH__