mem-cache: Create MRU replacement policy

Implementation of a Most Recently Used replacement policy.

Change-Id: Id52cb247ca25d4523dcc53490d113695dac6a3f1
Reviewed-on: https://gem5-review.googlesource.com/8889
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>

src/mem/cache/replacement_policies/ReplacementPolicies.py

@@ -40,6 +40,11 @@ class LRURP(BaseReplacementPolicy):
     cxx_class = 'LRURP'
     cxx_header = "mem/cache/replacement_policies/lru_rp.hh"
 
+class MRURP(BaseReplacementPolicy):
+    type = 'MRURP'
+    cxx_class = 'MRURP'
+    cxx_header = "mem/cache/replacement_policies/mru_rp.hh"
+
 class RandomRP(BaseReplacementPolicy):
     type = 'RandomRP'
     cxx_class = 'RandomRP'

src/mem/cache/replacement_policies/SConscript

@@ -34,4 +34,5 @@ SimObject('ReplacementPolicies.py')
 
 Source('base.cc')
 Source('lru_rp.cc')
+Source('mru_rp.cc')
 Source('random_rp.cc')

src/mem/cache/replacement_policies/mru_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/mru_rp.hh"
+
+#include "debug/CacheRepl.hh"
+
+MRURP::MRURP(const Params *p)
+    : BaseReplacementPolicy(p)
+{
+}
+
+void
+MRURP::touch(CacheBlk *blk)
+{
+    BaseReplacementPolicy::touch(blk);
+
+    // Update last touch timestamp
+    blk->lastTouchTick = curTick();
+}
+
+void
+MRURP::reset(CacheBlk *blk)
+{
+    BaseReplacementPolicy::reset(blk);
+
+    // Set last touch timestamp
+    blk->lastTouchTick = blk->tickInserted;
+}
+
+CacheBlk*
+MRURP::getVictim(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;
+}
+
+MRURP*
+MRURPParams::create()
+{
+    return new MRURP(this);
+}

src/mem/cache/replacement_policies/mru_rp.hh

@@ -0,0 +1,83 @@
+/**
+ * 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 Most Recently Used replacement policy.
+ * The victim is chosen using the timestamp. The block that was accessed the
+ * last is the one chosen to be replaced.
+ */
+
+#ifndef __MEM_CACHE_REPLACEMENT_POLICIES_MRU_RP_HH__
+#define __MEM_CACHE_REPLACEMENT_POLICIES_MRU_RP_HH__
+
+#include "mem/cache/replacement_policies/base.hh"
+#include "params/MRURP.hh"
+
+class MRURP : public BaseReplacementPolicy
+{
+  public:
+    /** Convenience typedef. */
+    typedef MRURPParams Params;
+
+    /**
+     * Construct and initiliaze this replacement policy.
+     */
+    MRURP(const Params *p);
+
+    /**
+     * Destructor.
+     */
+    ~MRURP() {}
+
+    /**
+     * 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 access timestamps.
+     * @param cands Replacement candidates, selected by indexing policy.
+     * @return Cache block to be replaced.
+     */
+    CacheBlk* getVictim(ReplacementCandidates& candidates) override;
+};
+
+#endif // __MEM_CACHE_REPLACEMENT_POLICIES_MRU_RP_HH__