mem-cache: Create BRRIP replacement policy

Implementation of a Bimodal Re-Reference Interval Prediction
replacement policy.

Change-Id: I25d4a59a60ef7ac496c66852e394fd6cbaf50912
Reviewed-on: https://gem5-review.googlesource.com/8891
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>

src/mem/cache/blk.hh

@@ -129,6 +129,11 @@ class CacheBlk
      */
     Tick lastTouchTick;
 
+    /**
+     * Re-Reference Interval Prediction Value. Used with RRIP repl policy.
+     */
+    unsigned rrpv;
+
   protected:
     /**
      * Represents that the indicated thread context has a "lock" on

src/mem/cache/replacement_policies/ReplacementPolicies.py

@@ -54,3 +54,13 @@ class RandomRP(BaseReplacementPolicy):
     type = 'RandomRP'
     cxx_class = 'RandomRP'
     cxx_header = "mem/cache/replacement_policies/random_rp.hh"
+
+class BRRIPRP(BaseReplacementPolicy):
+    type = 'BRRIPRP'
+    cxx_class = 'BRRIPRP'
+    cxx_header = "mem/cache/replacement_policies/brrip_rp.hh"
+    max_RRPV = Param.Unsigned(3, "Maximum RRPV possible")
+    hit_priority = Param.Bool(False,
+        "Prioritize evicting blocks that havent had a hit recently")
+    btp = Param.Percent(3,
+        "Percentage of blocks to be inserted with long RRPV")

src/mem/cache/replacement_policies/SConscript

@@ -33,6 +33,7 @@ Import('*')
 SimObject('ReplacementPolicies.py')
 
 Source('base.cc')
+Source('brrip_rp.cc')
 Source('fifo_rp.cc')
 Source('lru_rp.cc')
 Source('mru_rp.cc')

src/mem/cache/replacement_policies/brrip_rp.cc

@@ -0,0 +1,121 @@
+/**
+ * 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/brrip_rp.hh"
+
+#include "base/random.hh"
+#include "debug/CacheRepl.hh"
+
+BRRIPRP::BRRIPRP(const Params *p)
+    : BaseReplacementPolicy(p),
+      maxRRPV(p->max_RRPV), hitPriority(p->hit_priority), btp(p->btp)
+{
+    if (maxRRPV == 0){
+        fatal("max_RRPV should be greater than zero.\n");
+    }
+}
+
+void
+BRRIPRP::touch(CacheBlk *blk)
+{
+    BaseReplacementPolicy::touch(blk);
+
+    // Update RRPV if not 0 yet
+    // Every hit in HP mode makes the block the last to be evicted, while
+    // in FP mode a hit makes the block less likely to be evicted
+    if (hitPriority) {
+        blk->rrpv = 0;
+    } else if (blk->rrpv > 0) {
+        blk->rrpv--;
+    }
+}
+
+void
+BRRIPRP::reset(CacheBlk *blk)
+{
+    BaseReplacementPolicy::reset(blk);
+
+    // Reset RRPV
+    // Blocks are inserted as "long re-reference" if lower than btp,
+    // "distant re-reference" otherwise
+    if (random_mt.random<unsigned>(1, 100) <= btp) {
+        blk->rrpv = maxRRPV-1;
+    } else {
+        blk->rrpv = maxRRPV;
+    }
+}
+
+CacheBlk*
+BRRIPRP::getVictim(const ReplacementCandidates& candidates)
+{
+    // There must be at least one replacement candidate
+    assert(candidates.size() > 0);
+
+    // Use visitor to search for the victim
+    CacheBlk* blk = candidates[0];
+    for (const auto& candidate : candidates) {
+        // Stop iteration if found an invalid block
+        if (!candidate->isValid()) {
+            blk = candidate;
+            blk->rrpv = maxRRPV;
+            break;
+        // Update victim block if necessary
+        } else if (candidate->rrpv > blk->rrpv) {
+            blk = candidate;
+        }
+    }
+
+    // Make sure we don't have an invalid rrpv
+    assert(blk->rrpv <= maxRRPV);
+
+    // Get difference of block's RRPV to the highest possible RRPV in
+    // order to update the RRPV of all the other blocks accordingly
+    unsigned diff = maxRRPV - blk->rrpv;
+
+    // No need to update RRPV if there is no difference
+    if (diff > 0){
+        // Update RRPV of all candidates
+        for (const auto& candidate : candidates) {
+            // Update the block's RPPV with the new value
+            candidate->rrpv += diff;
+        }
+    }
+
+    DPRINTF(CacheRepl, "set %x, way %x: selecting blk for replacement\n",
+            blk->set, blk->way);
+
+    return blk;
+}
+
+BRRIPRP*
+BRRIPRPParams::create()
+{
+    return new BRRIPRP(this);
+}

src/mem/cache/replacement_policies/brrip_rp.hh

@@ -0,0 +1,124 @@
+/**
+ * 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 Re-Reference Interval Prediction replacement policy.
+ *
+ * Not-Recently Used (NRU) is an approximation of LRU that uses a single bit
+ * to determine if a block is going to be re-referenced in the near or distant
+ * future.
+ *
+ * Re-Reference Interval Prediction (RRIP) is an extension of NRU that uses a
+ * re-reference prediction value to determine if blocks are going to be re-
+ * used in the near future or not.
+ *
+ * The higher the value of the RRPV, the more distant the block is from
+ * its next access.
+ *
+ * Bimodal Re-Reference Interval Prediction (BRRIP) is an extension of RRIP
+ * that has a probability of not inserting blocks as the LRU. This probability
+ * is controlled by the bimodal throtle parameter (btp).
+ *
+ * From the original paper, this implementation of RRIP is also called
+ * Static RRIP (SRRIP), as it always inserts blocks with the same RRPV.
+ */
+
+#ifndef __MEM_CACHE_REPLACEMENT_POLICIES_BRRIP_RP_HH__
+#define __MEM_CACHE_REPLACEMENT_POLICIES_BRRIP_RP_HH__
+
+#include "mem/cache/replacement_policies/base.hh"
+#include "params/BRRIPRP.hh"
+
+class BRRIPRP : public BaseReplacementPolicy
+{
+  protected:
+    /**
+     * Maximum Re-Reference Prediction Value possible. A block with this
+     * value as the rrpv has the longest possible re-reference interval,
+     * that is, it is likely not to be used in the near future, and is
+     * among the best eviction candidates.
+     * A maxRRPV of 1 implies in a NRU.
+     */
+    const unsigned maxRRPV;
+
+    /**
+     * The hit priority (HP) policy replaces blocks that do not receive cache
+     * hits over any cache block that receives a hit, while the frequency
+     * priority (FP) policy replaces infrequently re-referenced blocks.
+     */
+    const bool hitPriority;
+
+    /**
+     * Bimodal throtle parameter. Value in the range [0,100] used to decide
+     * if a new block is inserted with long or distant re-reference.
+     */
+    const unsigned btp;
+
+  public:
+    /** Convenience typedef. */
+    typedef BRRIPRPParams Params;
+
+    /**
+     * Construct and initiliaze this replacement policy.
+     */
+    BRRIPRP(const Params *p);
+
+    /**
+     * Destructor.
+     */
+    ~BRRIPRP() {}
+
+    /**
+     * Touch a block to update its replacement data.
+     *
+     * @param blk Cache block to be touched.
+     */
+    void touch(CacheBlk *blk) override;
+
+    /**
+     * Reset replacement data for a block. Used when a block is inserted.
+     * Sets the insertion tick, and update correspondent replacement data.
+     * Set RRPV according to the insertion policy used.
+     *
+     * @param blk Cache block to be reset.
+     */
+    void reset(CacheBlk *blk) override;
+
+    /**
+     * Find replacement victim using rrpv.
+     *
+     * @param cands Replacement candidates, selected by indexing policy.
+     * @return Cache block to be replaced.
+     */
+    CacheBlk* getVictim(const ReplacementCandidates& candidates) override;
+};
+
+#endif // __MEM_CACHE_REPLACEMENT_POLICIES_BRRIP_RP_HH__