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>

1 files changed, 121 insertions, 0 deletions

diff --git a/src/mem/cache/replacement_policies/brrip_rp.cc b/src/mem/cache/replacement_policies/brrip_rp.cc
new file mode 100644
index 000000000..9185638d7
--- /dev/null
+++ b/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);
+}