mem-cache: Sandbox Based Optimal Offset Implementation

Brown, N. T., & Sendag, R. Sandbox Based Optimal Offset Estimation.

Change-Id: Ieb693b6b2c3d8bdfb6948389ca10e92c85454862
Reviewed-on: https://gem5-review.googlesource.com/c/15095
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>

4 files changed, 317 insertions, 0 deletions

diff --git a/src/mem/cache/prefetch/Prefetcher.py b/src/mem/cache/prefetch/Prefetcher.py
index 31d748698..e29f121ca 100644
--- a/src/mem/cache/prefetch/Prefetcher.py
+++ b/src/mem/cache/prefetch/Prefetcher.py
@@ -363,3 +363,13 @@ class BOPPrefetcher(QueuedPrefetcher):
     delay_queue_cycles = Param.Cycles(60,
                 "Cycles to delay a write in the left RR table from the delay \
                 queue")
+
+class SBOOEPrefetcher(QueuedPrefetcher):
+    type = 'SBOOEPrefetcher'
+    cxx_class = 'SBOOEPrefetcher'
+    cxx_header = "mem/cache/prefetch/sbooe.hh"
+    latency_buffer_size = Param.Int(32, "Entries in the latency buffer")
+    sequential_prefetchers = Param.Int(9, "Number of sequential prefetchers")
+    sandbox_entries = Param.Int(1024, "Size of the address buffer")
+    score_threshold_pct = Param.Percent(25, "Min. threshold to issue a \
+        prefetch. The value is the percentage of sandbox entries to use")
diff --git a/src/mem/cache/prefetch/SConscript b/src/mem/cache/prefetch/SConscript
index d87b694ed..c96ec4e34 100644
--- a/src/mem/cache/prefetch/SConscript
+++ b/src/mem/cache/prefetch/SConscript
@@ -38,6 +38,7 @@ Source('bop.cc')
 Source('delta_correlating_prediction_tables.cc')
 Source('irregular_stream_buffer.cc')
 Source('queued.cc')
+Source('sbooe.cc')
 Source('signature_path.cc')
 Source('signature_path_v2.cc')
 Source('slim_ampm.cc')
diff --git a/src/mem/cache/prefetch/sbooe.cc b/src/mem/cache/prefetch/sbooe.cc
new file mode 100644
index 000000000..e1bba9302
--- /dev/null
+++ b/src/mem/cache/prefetch/sbooe.cc
@@ -0,0 +1,148 @@
+/**
+ * Copyright (c) 2018 Metempsy Technology Consulting
+ * 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: Ivan Pizarro
+ */
+
+#include "mem/cache/prefetch/sbooe.hh"
+
+#include "debug/HWPrefetch.hh"
+#include "params/SBOOEPrefetcher.hh"
+
+SBOOEPrefetcher::SBOOEPrefetcher(const SBOOEPrefetcherParams *p)
+    : QueuedPrefetcher(p),
+      latencyBufferSize(p->latency_buffer_size),
+      sequentialPrefetchers(p->sequential_prefetchers),
+      scoreThreshold((p->sandbox_entries*p->score_threshold_pct)/100),
+      averageAccessLatency(0), latencyBufferSum(0),
+      bestSandbox(NULL),
+      accesses(0)
+{
+    if (!(p->score_threshold_pct >= 0 && p->score_threshold_pct <= 100)) {
+        fatal("%s: the score threshold should be between 0 and 100\n", name());
+    }
+
+    // Initialize a sandbox for every sequential prefetcher between
+    // -1 and the number of sequential prefetchers defined
+    for (int i = 0; i < sequentialPrefetchers; i++) {
+        sandboxes.push_back(Sandbox(p->sandbox_entries, i-1));
+    }
+}
+
+void
+SBOOEPrefetcher::Sandbox::insert(Addr addr, Tick tick)
+{
+    entries[index].valid = true;
+    entries[index].line = addr + stride;
+    entries[index].expectedArrivalTick = tick;
+
+    index++;
+
+    if (index == entries.size()) {
+        index = 0;
+    }
+}
+
+bool
+SBOOEPrefetcher::access(Addr access_line)
+{
+    for (Sandbox &sb : sandboxes) {
+        // Search for the address in the FIFO queue
+        for (const SandboxEntry &entry: sb.entries) {
+            if (entry.valid && entry.line == access_line) {
+                sb.sandboxScore++;
+                if (entry.expectedArrivalTick > curTick()) {
+                    sb.lateScore++;
+                }
+            }
+        }
+
+        sb.insert(access_line, curTick() + averageAccessLatency);
+
+        if (bestSandbox == NULL || sb.score() > bestSandbox->score()) {
+            bestSandbox = &sb;
+        }
+    }
+
+    accesses++;
+
+    return (accesses >= sandboxes.size());
+}
+
+void
+SBOOEPrefetcher::notifyFill(const PacketPtr& pkt)
+{
+    // (1) Look for the address in the demands list
+    // (2) Calculate the elapsed cycles until it was filled (curTick)
+    // (3) Insert the latency into the latency buffer (FIFO)
+    // (4) Calculate the new average access latency
+
+    auto it = demandAddresses.find(pkt->getAddr());
+
+    if (it != demandAddresses.end()) {
+        Tick elapsed_ticks = curTick() - it->second;
+
+        latencyBuffer.push_back(elapsed_ticks);
+        latencyBufferSum += elapsed_ticks;
+
+        if (latencyBuffer.size() > latencyBufferSize) {
+            latencyBufferSum -= latencyBuffer.front();
+            latencyBuffer.pop_front();
+        }
+
+        averageAccessLatency = latencyBufferSum / latencyBuffer.size();
+
+        demandAddresses.erase(it);
+    }
+}
+
+void
+SBOOEPrefetcher::calculatePrefetch(const PrefetchInfo &pfi,
+                                   std::vector<AddrPriority> &addresses)
+{
+    const Addr pfi_addr = pfi.getAddr();
+    const Addr pfi_line = pfi_addr >> lBlkSize;
+
+    auto it = demandAddresses.find(pfi_addr);
+
+    if (it == demandAddresses.end()) {
+        demandAddresses.insert(std::pair<Addr, Tick>(pfi_addr, curTick()));
+    }
+
+    const bool evaluationFinished = access(pfi_line);
+
+    if (evaluationFinished && bestSandbox->score() > scoreThreshold) {
+        Addr pref_line = pfi_line + bestSandbox->stride;
+        addresses.push_back(AddrPriority(pref_line << lBlkSize, 0));
+    }
+}
+
+SBOOEPrefetcher*
+SBOOEPrefetcherParams::create()
+{
+    return new SBOOEPrefetcher(this);
+}
diff --git a/src/mem/cache/prefetch/sbooe.hh b/src/mem/cache/prefetch/sbooe.hh
new file mode 100644
index 000000000..7fa5c35d3
--- /dev/null
+++ b/src/mem/cache/prefetch/sbooe.hh
@@ -0,0 +1,158 @@
+/**
+ * Copyright (c) 2018 Metempsy Technology Consulting
+ * 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: Ivan Pizarro
+ */
+
+/**
+ * Implementation of the 'Sandbox Based Optimal Offset Estimation'
+ * Reference:
+ *   Brown, N. T., & Sendag, R. Sandbox Based Optimal Offset Estimation.
+*/
+
+#ifndef __MEM_CACHE_PREFETCH_SBOOE_HH__
+#define __MEM_CACHE_PREFETCH_SBOOE_HH__
+
+#include <deque>
+#include <unordered_map>
+#include <vector>
+
+#include "mem/cache/prefetch/queued.hh"
+#include "mem/packet.hh"
+
+struct SBOOEPrefetcherParams;
+
+class SBOOEPrefetcher : public QueuedPrefetcher
+{
+    private:
+
+        /** Prefetcher parameters */
+        const int latencyBufferSize;
+        const int sequentialPrefetchers;
+
+        /** Threshold used to issue prefetchers */
+        const unsigned int scoreThreshold;
+
+        /**
+         * Holds the current demand addresses and tick. This is later used to
+         * calculate the average latency buffer when the address is filled in
+         * the cache.
+         */
+        std::unordered_map<Addr, Tick> demandAddresses;
+
+        /**
+         * The latency buffer holds the elapsed ticks between the demand and
+         * the fill in the cache for the latest N accesses which are used to
+         * calculate the average access latency which is later used to
+         * predict if a prefetcher would be filled on time if issued.
+         */
+        std::deque<Tick> latencyBuffer;
+
+        /** Holds the current average access latency */
+        Tick averageAccessLatency;
+
+        /** Holds the current sum of the latency buffer latency */
+        Tick latencyBufferSum;
+
+        struct SandboxEntry {
+            /** Cache line predicted by the candidate prefetcher */
+            Addr line;
+            /** Tick when the simulated prefetch is expected to be filled */
+            Tick expectedArrivalTick;
+            /** To indicate if it was initialized */
+            bool valid;
+
+            SandboxEntry()
+                : valid(false)
+            {}
+        };
+
+        struct Sandbox {
+            /** FIFO queue. Max entries is 'sandboxEntries' */
+            std::vector<SandboxEntry> entries;
+            /**
+             * Accesses during the eval period that were present
+             * in the sandbox
+             */
+            unsigned int sandboxScore;
+            /** Hits in the sandbox that wouldn't have been filled on time */
+            unsigned int lateScore;
+            /** Index of the oldest entry in the FIFO */
+            unsigned int index;
+            /** Sequential stride for this prefetcher */
+            const int stride;
+
+            Sandbox(unsigned int max_entries, int _stride)
+                : sandboxScore(0), lateScore(0), index(0), stride(_stride)
+            {
+                entries.resize(max_entries);
+            }
+
+            /**
+             * Insert the line address being accessed to the cache into the
+             * FIFO queue of the sandbox.
+             * @param line Line address being accessed
+             * @param tick Tick in which the access is expected to be filled
+             */
+            void insert(Addr line, Tick tick);
+
+            /** Calculate the useful score
+             *  @return Useful score of the sandbox. Sandbox score adjusted by
+             *          by the late score
+             */
+            unsigned int score() const {
+                return (sandboxScore - lateScore);
+            }
+        };
+
+        std::vector<Sandbox> sandboxes;
+
+        /** Current best sandbox */
+        Sandbox * bestSandbox;
+
+        /** Number of accesses notified to the prefetcher */
+        unsigned int accesses;
+
+        /**
+         * Process an access to the specified line address and update the
+         * sandbox counters counters.
+         * @param line Address of the line being accessed
+         * @return TRUE if the evaluation finished, FALSE otherwise
+         */
+        bool access(Addr line);
+
+        /** Update the latency buffer after a prefetch fill */
+        void notifyFill(const PacketPtr& pkt) override;
+
+    public:
+        SBOOEPrefetcher(const SBOOEPrefetcherParams *p);
+
+        void calculatePrefetch(const PrefetchInfo &pfi,
+                               std::vector<AddrPriority> &addresses) override;
+};
+
+#endif // __MEM_CACHE_PREFETCH_SBOOE_HH__