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>

8 files changed, 563 insertions, 0 deletions

diff --git a/src/mem/cache/replacement_policies/ReplacementPolicies.py b/src/mem/cache/replacement_policies/ReplacementPolicies.py
new file mode 100644
index 000000000..64743819b
--- /dev/null
+++ b/src/mem/cache/replacement_policies/ReplacementPolicies.py
@@ -0,0 +1,46 @@
+# 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
+
+from m5.params import *
+from m5.proxy import *
+from m5.SimObject import SimObject
+
+class BaseReplacementPolicy(SimObject):
+    type = 'BaseReplacementPolicy'
+    abstract = True
+    cxx_header = "mem/cache/replacement_policies/base.hh"
+
+class LRURP(BaseReplacementPolicy):
+    type = 'LRURP'
+    cxx_class = 'LRURP'
+    cxx_header = "mem/cache/replacement_policies/lru_rp.hh"
+
+class RandomRP(BaseReplacementPolicy):
+    type = 'RandomRP'
+    cxx_class = 'RandomRP'
+    cxx_header = "mem/cache/replacement_policies/random_rp.hh"
diff --git a/src/mem/cache/replacement_policies/SConscript b/src/mem/cache/replacement_policies/SConscript
new file mode 100644
index 000000000..c3c89923f
--- /dev/null
+++ b/src/mem/cache/replacement_policies/SConscript
@@ -0,0 +1,37 @@
+# -*- mode:python -*-
+
+# 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
+
+Import('*')
+
+SimObject('ReplacementPolicies.py')
+
+Source('base.cc')
+Source('lru_rp.cc')
+Source('random_rp.cc')
diff --git a/src/mem/cache/replacement_policies/base.cc b/src/mem/cache/replacement_policies/base.cc
new file mode 100644
index 000000000..c422a75d8
--- /dev/null
+++ b/src/mem/cache/replacement_policies/base.cc
@@ -0,0 +1,66 @@
+/**
+ * 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 common base class for cache replacement policy objects.
+ * In general replacement policies try to use invalid entries as victims,
+ * and if no such blocks exist the replacement policy is applied.
+ */
+
+#include "mem/cache/replacement_policies/base.hh"
+
+BaseReplacementPolicy::BaseReplacementPolicy(const Params *p)
+    : SimObject(p)
+{
+}
+
+void
+BaseReplacementPolicy::touch(CacheBlk *blk)
+{
+    // Inform block has been touched
+    blk->isTouched = true;
+
+    // Update frequency counter
+    blk->refCount++;
+}
+
+void
+BaseReplacementPolicy::reset(CacheBlk *blk)
+{
+    // Inform block has been touched
+    blk->isTouched = true;
+
+    // Set insertion tick
+    blk->tickInserted = curTick();
+
+    // Reset frequency counter
+    blk->refCount = 0;
+}
diff --git a/src/mem/cache/replacement_policies/base.hh b/src/mem/cache/replacement_policies/base.hh
new file mode 100644
index 000000000..383f3f01a
--- /dev/null
+++ b/src/mem/cache/replacement_policies/base.hh
@@ -0,0 +1,105 @@
+/**
+ * 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
+ */
+
+#ifndef __MEM_CACHE_REPLACEMENT_POLICIES_BASE_HH__
+#define __MEM_CACHE_REPLACEMENT_POLICIES_BASE_HH__
+
+#include "mem/cache/base.hh"
+#include "mem/cache/blk.hh"
+#include "params/BaseReplacementPolicy.hh"
+#include "sim/sim_object.hh"
+
+/**
+ * Replacement candidates as chosen by the indexing policy.
+ *
+ * The base functions touch() and reset() must be called by all subclasses
+ * that override them.
+ *
+ * @todo
+ *   Currently the replacement candidates are simply the cache blocks
+ *   derived from the possible placement locations of an address, as
+ *   defined by the getPossibleLocations() from BaseTags. In a future
+ *   patch it should be an inheritable class to allow the replacement
+ *   policies to be used with any table-like structure that needs to
+ *   replace its entries.
+ */
+typedef std::vector<CacheBlk*> ReplacementCandidates;
+
+/**
+ * A common base class of cache replacement policy objects.
+ */
+class BaseReplacementPolicy : public SimObject
+{
+  public:
+    /**
+      * Convenience typedef.
+      */
+    typedef BaseReplacementPolicyParams Params;
+
+    /**
+     * Construct and initiliaze this replacement policy.
+     */
+    BaseReplacementPolicy(const Params *p);
+
+    /**
+     * Destructor.
+     */
+    virtual ~BaseReplacementPolicy() {}
+
+    /**
+     * Touch a block to update its replacement data.
+     * Updates number of references.
+     *
+     * This base function must be called by all subclasses that override it.
+     *
+     * @param blk Cache block to be touched.
+     */
+    virtual void touch(CacheBlk *blk);
+
+    /**
+     * Reset replacement data for a block. Used when a block is inserted.
+     * Sets the insertion tick, and update number of references.
+     *
+     * This base function must be called by all subclasses that override it.
+     *
+     * @param blk Cache block to be reset.
+     */
+    virtual void reset(CacheBlk *blk);
+
+    /**
+     * Find replacement victim among candidates.
+     *
+     * @param candidates Replacement candidates, selected by indexing policy.
+     * @return Cache block to be replaced.
+     */
+    virtual CacheBlk* getVictim(const ReplacementCandidates& candidates) = 0;
+};
+
+#endif // __MEM_CACHE_REPLACEMENT_POLICIES_BASE_HH__
diff --git a/src/mem/cache/replacement_policies/lru_rp.cc b/src/mem/cache/replacement_policies/lru_rp.cc
new file mode 100644
index 000000000..b2fa20b6f
--- /dev/null
+++ b/src/mem/cache/replacement_policies/lru_rp.cc
@@ -0,0 +1,87 @@
+/**
+ * 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/lru_rp.hh"
+
+#include "debug/CacheRepl.hh"
+
+LRURP::LRURP(const Params *p)
+    : BaseReplacementPolicy(p)
+{
+}
+
+void
+LRURP::touch(CacheBlk *blk)
+{
+    BaseReplacementPolicy::touch(blk);
+
+    // Update last touch timestamp
+    blk->lastTouchTick = curTick();
+}
+
+void
+LRURP::reset(CacheBlk *blk)
+{
+    BaseReplacementPolicy::reset(blk);
+
+    // Set last touch timestamp
+    blk->lastTouchTick = blk->tickInserted;
+}
+
+CacheBlk*
+LRURP::getVictim(const ReplacementCandidates& candidates)
+{
+    // There must be at least one replacement candidate
+    assert(candidates.size() > 0);
+
+    // Visit all candidates to find victim
+    CacheBlk* blk = candidates[0];
+    for (const auto& candidate : candidates) {
+        // Stop iteration if found an invalid block
+        if (!candidate->isValid()) {
+            blk = candidate;
+            break;
+        // Update victim block if necessary
+        } else if (candidate->lastTouchTick < blk->lastTouchTick) {
+            blk = candidate;
+        }
+    }
+
+    DPRINTF(CacheRepl, "set %x, way %x: selecting blk for replacement\n",
+            blk->set, blk->way);
+
+    return blk;
+}
+
+LRURP*
+LRURPParams::create()
+{
+    return new LRURP(this);
+}
diff --git a/src/mem/cache/replacement_policies/lru_rp.hh b/src/mem/cache/replacement_policies/lru_rp.hh
new file mode 100644
index 000000000..3e5efe61f
--- /dev/null
+++ b/src/mem/cache/replacement_policies/lru_rp.hh
@@ -0,0 +1,84 @@
+/**
+ * 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__
diff --git a/src/mem/cache/replacement_policies/random_rp.cc b/src/mem/cache/replacement_policies/random_rp.cc
new file mode 100644
index 000000000..1c54bdac6
--- /dev/null
+++ b/src/mem/cache/replacement_policies/random_rp.cc
@@ -0,0 +1,71 @@
+/**
+ * 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/random_rp.hh"
+
+#include "base/random.hh"
+#include "debug/CacheRepl.hh"
+
+RandomRP::RandomRP(const Params *p)
+    : BaseReplacementPolicy(p)
+{
+}
+
+CacheBlk*
+RandomRP::getVictim(const ReplacementCandidates& candidates)
+{
+    // There must be at least one replacement candidate
+    assert(candidates.size() > 0);
+
+    // Choose one candidate at random
+    CacheBlk* blk = candidates[random_mt.random<unsigned>(0,
+                                    candidates.size() - 1)];
+
+    // Visit all candidates to find an invalid entry
+    for (const auto& candidate : candidates) {
+        // Give priority to victimise invalid entries
+        if (!candidate->isValid()){
+            blk = candidate;
+            break;
+        }
+    }
+
+    // If no invalid blocks were found, choose one of the candidates randomly
+    DPRINTF(CacheRepl, "set %x, way %x: selecting blk for replacement\n",
+            blk->set, blk->way);
+
+    return blk;
+}
+
+RandomRP*
+RandomRPParams::create()
+{
+    return new RandomRP(this);
+}
diff --git a/src/mem/cache/replacement_policies/random_rp.hh b/src/mem/cache/replacement_policies/random_rp.hh
new file mode 100644
index 000000000..338b26ff2
--- /dev/null
+++ b/src/mem/cache/replacement_policies/random_rp.hh
@@ -0,0 +1,67 @@
+/**
+ * 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 random replacement policy.
+ * The victim is chosen at random, if there are no invalid entries.
+ */
+
+#ifndef __MEM_CACHE_REPLACEMENT_POLICIES_RANDOM_RP_HH__
+#define __MEM_CACHE_REPLACEMENT_POLICIES_RANDOM_RP_HH__
+
+#include "mem/cache/replacement_policies/base.hh"
+#include "params/RandomRP.hh"
+
+class RandomRP : public BaseReplacementPolicy
+{
+  public:
+    /** Convenience typedef. */
+    typedef RandomRPParams Params;
+
+    /**
+     * Construct and initiliaze this replacement policy.
+     */
+    RandomRP(const Params *p);
+
+    /**
+     * Destructor.
+     */
+    ~RandomRP() {}
+
+    /**
+     * Find replacement victim at random.
+     * @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_RANDOM_RP_HH__