mem-cache: Signature Path Prefetcher
Related paper:
Lookahead Prefetching with Signature Path
J Kim, PV Gratz, ALN Reddy
The 2nd Data Prefetching Championship (DPC2), 2015
Change-Id: I2319be2fa409f955f65e1bf1e1bb2d6d9a4fea11
Reviewed-on: https://gem5-review.googlesource.com/c/14737
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
diff --git a/src/mem/cache/prefetch/Prefetcher.py b/src/mem/cache/prefetch/Prefetcher.py
index df547ed..a868a25 100644
--- a/src/mem/cache/prefetch/Prefetcher.py
+++ b/src/mem/cache/prefetch/Prefetcher.py
@@ -40,6 +40,7 @@
# Mitch Hayenga
from ClockedObject import ClockedObject
+from IndexingPolicies import *
from m5.SimObject import *
from m5.params import *
from m5.proxy import *
@@ -139,3 +140,42 @@
cxx_header = "mem/cache/prefetch/tagged.hh"
degree = Param.Int(2, "Number of prefetches to generate")
+
+class SignaturePathPrefetcher(QueuedPrefetcher):
+ type = 'SignaturePathPrefetcher'
+ cxx_class = 'SignaturePathPrefetcher'
+ cxx_header = "mem/cache/prefetch/signature_path.hh"
+
+ signature_shift = Param.UInt8(3,
+ "Number of bits to shift when calculating a new signature");
+ signature_bits = Param.UInt16(12,
+ "Size of the signature, in bits");
+ signature_table_entries = Param.MemorySize("1024",
+ "Number of entries of the signature table")
+ signature_table_assoc = Param.Unsigned(2,
+ "Associativity of the signature table")
+ signature_table_indexing_policy = Param.BaseIndexingPolicy(
+ SetAssociative(entry_size = 1, assoc = Parent.signature_table_assoc,
+ size = Parent.signature_table_entries),
+ "Indexing policy of the signature table")
+ signature_table_replacement_policy = Param.BaseReplacementPolicy(LRURP(),
+ "Replacement policy of the signature table")
+
+ max_counter_value = Param.UInt8(7, "Maximum pattern counter value")
+ pattern_table_entries = Param.MemorySize("4096",
+ "Number of entries of the pattern table")
+ pattern_table_assoc = Param.Unsigned(1,
+ "Associativity of the pattern table")
+ strides_per_pattern_entry = Param.Unsigned(4,
+ "Number of strides stored in each pattern entry")
+ pattern_table_indexing_policy = Param.BaseIndexingPolicy(
+ SetAssociative(entry_size = 1, assoc = Parent.pattern_table_assoc,
+ size = Parent.pattern_table_entries),
+ "Indexing policy of the pattern table")
+ pattern_table_replacement_policy = Param.BaseReplacementPolicy(LRURP(),
+ "Replacement policy of the pattern table")
+
+ prefetch_confidence_threshold = Param.Float(0.5,
+ "Minimum confidence to issue prefetches")
+ lookahead_confidence_threshold = Param.Float(0.75,
+ "Minimum confidence to continue exploring lookahead entries")
diff --git a/src/mem/cache/prefetch/SConscript b/src/mem/cache/prefetch/SConscript
index 2665d18..ccbc2e3 100644
--- a/src/mem/cache/prefetch/SConscript
+++ b/src/mem/cache/prefetch/SConscript
@@ -34,6 +34,6 @@
Source('base.cc')
Source('queued.cc')
+Source('signature_path.cc')
Source('stride.cc')
Source('tagged.cc')
-
diff --git a/src/mem/cache/prefetch/associative_set.hh b/src/mem/cache/prefetch/associative_set.hh
new file mode 100644
index 0000000..99b6a6d
--- /dev/null
+++ b/src/mem/cache/prefetch/associative_set.hh
@@ -0,0 +1,200 @@
+/**
+ * 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: Javier Bueno
+ */
+
+#ifndef __CACHE_PREFETCH_ASSOCIATIVE_SET_HH__
+#define __CACHE_PREFETCH_ASSOCIATIVE_SET_HH__
+
+#include "mem/cache/replacement_policies/base.hh"
+#include "mem/cache/replacement_policies/replaceable_entry.hh"
+#include "mem/cache/tags/indexing_policies/base.hh"
+
+/**
+ * Entry used for set-associative tables, usable with replacement policies
+ */
+class TaggedEntry : public ReplaceableEntry {
+ /** Tag for the entry */
+ Addr tag;
+ /** Valid bit */
+ bool valid;
+ /** Whether this entry refers to a memory area in the secure space */
+ bool secure;
+ public:
+ TaggedEntry() : tag(0), valid(false), secure(false) {}
+ virtual ~TaggedEntry() {}
+
+ /**
+ * Consult the valid bit
+ * @return True if the entry is valid
+ */
+ bool isValid() const
+ {
+ return valid;
+ }
+
+ /**
+ * Sets the entry to valid
+ */
+ void setValid()
+ {
+ valid = true;
+ }
+
+ /**
+ * Sets the entry to invalid
+ */
+ void setInvalid() {
+ valid = false;
+ }
+
+ /**
+ * Obtain the entry tag
+ * @return the tag value
+ */
+ Addr getTag() const
+ {
+ return tag;
+ }
+
+ /**
+ * Sets the tag of the entry
+ * @param t the tag value
+ */
+ void setTag(Addr t)
+ {
+ tag = t;
+ }
+
+ /**
+ * Consult if this entry refers to a memory in the secure area
+ * @return True if this entry refers to secure memory area
+ */
+ bool isSecure() const
+ {
+ return secure;
+ }
+
+ /**
+ * Sets the secure value bit
+ * @param s secure bit value
+ */
+ void setSecure(bool s)
+ {
+ secure = s;
+ }
+
+ /**
+ * Resets the entry, this is called when an entry is evicted to allocate
+ * a new one. Types inheriting this class should provide its own
+ * implementation
+ */
+ virtual void reset () {
+ }
+};
+
+/**
+ * Associative container based on the previosuly defined Entry type
+ * Each element is indexed by a key of type Addr, an additional
+ * bool value is used as an additional tag data of the entry.
+ */
+template<class Entry>
+class AssociativeSet {
+ static_assert(std::is_base_of<TaggedEntry, Entry>::value,
+ "Entry must derive from TaggedEntry");
+
+ /** Associativity of the container */
+ const int associativity;
+ /**
+ * Total number of entries, entries are organized in sets of the provided
+ * associativity. The number of associative sets is obtained by dividing
+ * numEntries by associativity.
+ */
+ const int numEntries;
+ /** Pointer to the indexing policy */
+ BaseIndexingPolicy* const indexingPolicy;
+ /** Pointer to the replacement policy */
+ BaseReplacementPolicy* const replacementPolicy;
+ /** Vector containing the entries of the container */
+ std::vector<Entry> entries;
+
+ public:
+ /**
+ * Public constructor
+ * @param assoc number of elements in each associative set
+ * @param num_entries total number of entries of the container, the number
+ * of sets can be calculated dividing this balue by the 'assoc' value
+ * @param idx_policy indexing policy
+ * @param rpl_policy replacement policy
+ * @param initial value of the elements of the set
+ */
+ AssociativeSet(int assoc, int num_entries, BaseIndexingPolicy *idx_policy,
+ BaseReplacementPolicy *rpl_policy, Entry const &init_value =
+ Entry());
+
+ /**
+ * Find an entry within the set
+ * @param addr key element
+ * @param is_secure tag element
+ * @return returns a pointer to the wanted entry or nullptr if it does not
+ * exist.
+ */
+ Entry* findEntry(Addr addr, bool is_secure) const;
+
+ /**
+ * Do an access to the entry, this is required to
+ * update the replacement information data.
+ * @param entry the accessed entry
+ */
+ void accessEntry(Entry *entry);
+
+ /**
+ * Find a victim to be replaced
+ * @param addr key to select the possible victim
+ * @result entry to be victimized
+ */
+ Entry* findVictim(Addr addr);
+
+ /**
+ * Find the set of entries that could be replaced given
+ * that we want to add a new entry with the provided key
+ * @param addr key to select the set of entries
+ * @result vector of candidates matching with the provided key
+ */
+ std::vector<Entry *> getPossibleEntries(const Addr addr) const;
+
+ /**
+ * Indicate that an entry has just been inserted
+ * @param addr key of the container
+ * @param is_secure tag component of the container
+ * @param entry pointer to the container entry to be inserted
+ */
+ void insertEntry(Addr addr, bool is_secure, Entry* entry);
+};
+
+#endif//__CACHE_PREFETCH_ASSOCIATIVE_SET_HH__
diff --git a/src/mem/cache/prefetch/associative_set_impl.hh b/src/mem/cache/prefetch/associative_set_impl.hh
new file mode 100644
index 0000000..5e6e7c5
--- /dev/null
+++ b/src/mem/cache/prefetch/associative_set_impl.hh
@@ -0,0 +1,119 @@
+/**
+ * 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: Javier Bueno
+ */
+
+#ifndef __CACHE_PREFETCH_ASSOCIATIVE_SET_IMPL_HH__
+#define __CACHE_PREFETCH_ASSOCIATIVE_SET_IMPL_HH__
+
+#include "mem/cache/prefetch/associative_set.hh"
+
+template<class Entry>
+AssociativeSet<Entry>::AssociativeSet(int assoc, int num_entries,
+ BaseIndexingPolicy *idx_policy, BaseReplacementPolicy *rpl_policy,
+ Entry const &init_value)
+ : associativity(assoc), numEntries(num_entries), indexingPolicy(idx_policy),
+ replacementPolicy(rpl_policy), entries(numEntries, init_value)
+{
+ fatal_if(!isPowerOf2(num_entries), "The number of entries of an "
+ "AssociativeSet<> must be a power of 2");
+ fatal_if(!isPowerOf2(assoc), "The associativity of an AssociativeSet<> "
+ "must be a power of 2");
+ for (unsigned int entry_idx = 0; entry_idx < numEntries; entry_idx += 1) {
+ Entry* entry = &entries[entry_idx];
+ indexingPolicy->setEntry(entry, entry_idx);
+ entry->replacementData = replacementPolicy->instantiateEntry();
+ }
+}
+
+template<class Entry>
+Entry*
+AssociativeSet<Entry>::findEntry(Addr addr, bool is_secure) const
+{
+ Addr tag = indexingPolicy->extractTag(addr);
+ const std::vector<ReplaceableEntry*> selected_entries =
+ indexingPolicy->getPossibleEntries(addr);
+
+ for (const auto& location : selected_entries) {
+ Entry* entry = static_cast<Entry *>(location);
+ if ((entry->getTag() == tag) && entry->isValid() &&
+ entry->isSecure() == is_secure) {
+ return entry;
+ }
+ }
+ return nullptr;
+}
+
+template<class Entry>
+void
+AssociativeSet<Entry>::accessEntry(Entry *entry)
+{
+ replacementPolicy->touch(entry->replacementData);
+}
+
+template<class Entry>
+Entry*
+AssociativeSet<Entry>::findVictim(Addr addr)
+{
+ // Get possible entries to be victimized
+ const std::vector<ReplaceableEntry*> selected_entries =
+ indexingPolicy->getPossibleEntries(addr);
+ Entry* victim = static_cast<Entry*>(replacementPolicy->getVictim(
+ selected_entries));
+ // There is only one eviction for this replacement
+ victim->reset();
+ return victim;
+}
+
+
+template<class Entry>
+std::vector<Entry *>
+AssociativeSet<Entry>::getPossibleEntries(const Addr addr) const
+{
+ std::vector<ReplaceableEntry *> selected_entries =
+ indexingPolicy->getPossibleEntries(addr);
+ std::vector<Entry *> entries(selected_entries.size(), nullptr);
+
+ unsigned int idx = 0;
+ for (auto &entry : selected_entries) {
+ entries[idx++] = static_cast<Entry *>(entry);
+ }
+ return entries;
+}
+
+template<class Entry>
+void
+AssociativeSet<Entry>::insertEntry(Addr addr, bool is_secure, Entry* entry)
+{
+ entry->setValid();
+ entry->setTag(indexingPolicy->extractTag(addr));
+ entry->setSecure(is_secure);
+ replacementPolicy->reset(entry->replacementData);
+}
+
+#endif//__CACHE_PREFETCH_ASSOCIATIVE_SET_IMPL_HH__
diff --git a/src/mem/cache/prefetch/signature_path.cc b/src/mem/cache/prefetch/signature_path.cc
new file mode 100644
index 0000000..a0356b1
--- /dev/null
+++ b/src/mem/cache/prefetch/signature_path.cc
@@ -0,0 +1,275 @@
+/**
+ * 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: Javier Bueno
+ */
+
+#include "mem/cache/prefetch/signature_path.hh"
+
+#include <cassert>
+
+#include "debug/HWPrefetch.hh"
+#include "mem/cache/prefetch/associative_set_impl.hh"
+#include "params/SignaturePathPrefetcher.hh"
+
+SignaturePathPrefetcher::SignaturePathPrefetcher(
+ const SignaturePathPrefetcherParams *p)
+ : QueuedPrefetcher(p),
+ stridesPerPatternEntry(p->strides_per_pattern_entry),
+ signatureShift(p->signature_shift),
+ signatureBits(p->signature_bits),
+ maxCounterValue(p->max_counter_value),
+ prefetchConfidenceThreshold(p->prefetch_confidence_threshold),
+ lookaheadConfidenceThreshold(p->lookahead_confidence_threshold),
+ signatureTable(p->signature_table_assoc, p->signature_table_entries,
+ p->signature_table_indexing_policy,
+ p->signature_table_replacement_policy),
+ patternTable(p->pattern_table_assoc, p->pattern_table_entries,
+ p->pattern_table_indexing_policy,
+ p->pattern_table_replacement_policy,
+ PatternEntry(stridesPerPatternEntry))
+{
+}
+
+SignaturePathPrefetcher::PatternStrideEntry &
+SignaturePathPrefetcher::PatternEntry::getStrideEntry(stride_t stride,
+ uint8_t max_counter_value)
+{
+ PatternStrideEntry *pstride_entry = findStride(stride);
+ if (pstride_entry == nullptr) {
+ // Specific replacement algorithm for this table,
+ // pick the entry with the lowest counter value,
+ // then decrease the counter of all entries
+
+ // If all counters have the max value, this will be the pick
+ PatternStrideEntry *victim_pstride_entry = &(strideEntries[0]);
+
+ uint8_t current_counter = max_counter_value;
+ for (auto &entry : strideEntries) {
+ if (entry.counter < current_counter) {
+ victim_pstride_entry = &entry;
+ current_counter = entry.counter;
+ }
+ if (entry.counter > 0) {
+ entry.counter -= 1;
+ }
+ }
+ pstride_entry = victim_pstride_entry;
+ pstride_entry->counter = 0;
+ pstride_entry->stride = stride;
+ }
+ return *pstride_entry;
+}
+
+void
+SignaturePathPrefetcher::addPrefetch(Addr ppn, stride_t block,
+ bool is_secure, std::vector<AddrPriority> &addresses)
+{
+ /**
+ * block is relative to the provided ppn. Assuming a page size of 4kB and
+ * a block size of 64B, the range of the stride of this prefetcher is
+ * -63,63 (pageBytes/blkSize) as the last accessed block also ranges from
+ * 0,63, the block value is expected to be between -63 and 126
+ * Negative block means that we are accessing the lower contiguous page,
+ * 64 or greater point to the next contiguous.
+ */
+ assert(block > -((stride_t)(pageBytes/blkSize)));
+ assert(block < 2*((stride_t)(pageBytes/blkSize)));
+
+ Addr pf_ppn;
+ stride_t pf_block;
+ if (block < 0) {
+ pf_ppn = ppn - 1;
+ pf_block = block + (pageBytes/blkSize);
+ } else if (block >= (pageBytes/blkSize)) {
+ pf_ppn = ppn + 1;
+ pf_block = block - (pageBytes/blkSize);
+ } else {
+ pf_ppn = ppn;
+ pf_block = block;
+ }
+
+ Addr new_addr = pf_ppn * pageBytes;
+ new_addr += pf_block * (Addr)blkSize;
+
+ DPRINTF(HWPrefetch, "Queuing prefetch to %#x.\n", new_addr);
+ addresses.push_back(AddrPriority(new_addr, 0));
+}
+
+void
+SignaturePathPrefetcher::updatePatternTable(Addr signature, stride_t stride)
+{
+ assert(stride != 0);
+ // The pattern table is indexed by signatures
+ PatternEntry &p_entry = getPatternEntry(signature);
+ PatternStrideEntry &ps_entry = p_entry.getStrideEntry(stride,
+ maxCounterValue);
+ if (ps_entry.counter < maxCounterValue) {
+ ps_entry.counter += 1;
+ }
+}
+
+SignaturePathPrefetcher::SignatureEntry &
+SignaturePathPrefetcher::getSignatureEntry(Addr ppn, bool is_secure,
+ stride_t block, bool &miss)
+{
+ SignatureEntry* signature_entry = signatureTable.findEntry(ppn, is_secure);
+ if (signature_entry != nullptr) {
+ signatureTable.accessEntry(signature_entry);
+ miss = false;
+ } else {
+ signature_entry = signatureTable.findVictim(ppn);
+ assert(signature_entry != nullptr);
+
+ signatureTable.insertEntry(ppn, is_secure, signature_entry);
+ signature_entry->signature = block;
+ signature_entry->lastBlock = block;
+ miss = true;
+ }
+ return *signature_entry;
+}
+
+SignaturePathPrefetcher::PatternEntry &
+SignaturePathPrefetcher::getPatternEntry(Addr signature)
+{
+ PatternEntry* pattern_entry = patternTable.findEntry(signature, false);
+ if (pattern_entry != nullptr) {
+ // Signature found
+ patternTable.accessEntry(pattern_entry);
+ } else {
+ // Signature not found
+ pattern_entry = patternTable.findVictim(signature);
+ assert(pattern_entry != nullptr);
+
+ patternTable.insertEntry(signature, false, pattern_entry);
+ }
+ return *pattern_entry;
+}
+
+void
+SignaturePathPrefetcher::calculatePrefetch(const PrefetchInfo &pfi,
+ std::vector<AddrPriority> &addresses)
+{
+ Addr request_addr = pfi.getAddr();
+ Addr ppn = request_addr / pageBytes;
+ stride_t current_block = (request_addr % pageBytes) / blkSize;
+ stride_t stride;
+ bool is_secure = pfi.isSecure();
+
+ // Get the SignatureEntry of this page to:
+ // - compute the current stride
+ // - obtain the current signature of accesses
+ bool miss;
+ SignatureEntry &signature_entry = getSignatureEntry(ppn, is_secure,
+ current_block, miss);
+ if (miss) {
+ // No history for this page, can't continue
+ return;
+ }
+
+ stride = current_block - signature_entry.lastBlock;
+ if (stride == 0) {
+ // Can't continue with a stride 0
+ return;
+ }
+
+ // Update the confidence of the current signature
+ updatePatternTable(signature_entry.signature, stride);
+
+ // Update the current SignatureEntry signature and lastBlock
+ signature_entry.signature =
+ updateSignature(signature_entry.signature, stride);
+ signature_entry.lastBlock = current_block;
+
+ signature_t current_signature = signature_entry.signature;
+ double current_confidence = 1.0;
+ stride_t current_stride = signature_entry.lastBlock;
+
+ do {
+ // With the updated signature, attempt to generate prefetches
+ // - search the PatternTable and select all entries with enough
+ // confidence, these are prefetch candidates
+ // - select the entry with the highest counter as the "lookahead"
+ PatternEntry *current_pattern_entry =
+ patternTable.findEntry(current_signature, false);
+ PatternStrideEntry const *lookahead = nullptr;
+ if (current_pattern_entry != nullptr) {
+ uint8_t max_counter = 0;
+ for (auto const &entry : current_pattern_entry->strideEntries) {
+ //select the entry with the maximum counter value as lookahead
+ if (max_counter < entry.counter) {
+ max_counter = entry.counter;
+ lookahead = &entry;
+ }
+ double prefetch_confidence =
+ (double) entry.counter / maxCounterValue;
+
+ if (prefetch_confidence >= prefetchConfidenceThreshold) {
+ assert(entry.stride != 0);
+ //prefetch candidate
+ addPrefetch(ppn, current_stride + entry.stride,
+ is_secure, addresses);
+ }
+ }
+ }
+ if (lookahead != nullptr) {
+ // If a lookahead was selected, compute its confidence using
+ // the counter of its entry and the accumulated confidence
+ // if the confidence is high enough, generate a new signature
+ double lookahead_confidence;
+ if (lookahead->counter == maxCounterValue) {
+ // maximum confidence is 0.95, guaranteeing that
+ // current confidence will eventually fall beyond
+ // the threshold
+ lookahead_confidence = 0.95;
+ } else {
+ lookahead_confidence =
+ ((double) lookahead->counter / maxCounterValue);
+ }
+ current_confidence *= lookahead_confidence;
+ current_signature =
+ updateSignature(current_signature, lookahead->stride);
+ current_stride += lookahead->stride;
+ } else {
+ current_confidence = 0.0;
+ }
+ // If the accumulated confidence is high enough, keep repeating
+ // this process with the updated signature
+ }
+ while (current_confidence > lookaheadConfidenceThreshold);
+
+ if (addresses.empty()) {
+ // Enable the next line prefetcher if no prefetch candidates are found
+ addPrefetch(ppn, current_block + 1, is_secure, addresses);
+ }
+}
+
+SignaturePathPrefetcher*
+SignaturePathPrefetcherParams::create()
+{
+ return new SignaturePathPrefetcher(this);
+}
diff --git a/src/mem/cache/prefetch/signature_path.hh b/src/mem/cache/prefetch/signature_path.hh
new file mode 100644
index 0000000..0371b56
--- /dev/null
+++ b/src/mem/cache/prefetch/signature_path.hh
@@ -0,0 +1,204 @@
+/**
+ * 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: Javier Bueno
+ */
+
+ /**
+ * Implementation of the Signature Path Prefetcher
+ *
+ * References:
+ * Lookahead prefetching with signature path
+ * J Kim, PV Gratz, ALN Reddy
+ * The 2nd Data Prefetching Championship (DPC2)
+ * The filter feature described in the paper is not implemented, as it
+ * redundant prefetches are dropped by the cache.
+ */
+
+#ifndef __MEM_CACHE_PREFETCH_SIGNATURE_PATH_HH__
+#define __MEM_CACHE_PREFETCH_SIGNATURE_PATH_HH__
+
+#include "mem/cache/prefetch/associative_set.hh"
+#include "mem/cache/prefetch/queued.hh"
+#include "mem/packet.hh"
+
+struct SignaturePathPrefetcherParams;
+
+class SignaturePathPrefetcher : public QueuedPrefetcher
+{
+ /** Signature type */
+ typedef uint16_t signature_t;
+ /** Stride type */
+ typedef int16_t stride_t;
+
+ /** Number of strides stored in each pattern entry */
+ const unsigned stridesPerPatternEntry;
+ /** Number of bits to shift when generating a new signature */
+ const uint8_t signatureShift;
+ /** Size of the signature, in bits */
+ const signature_t signatureBits;
+ /** Maximum pattern entries counter value */
+ const uint8_t maxCounterValue;
+ /** Minimum confidence to issue a prefetch */
+ const double prefetchConfidenceThreshold;
+ /** Minimum confidence to keep navigating lookahead entries */
+ const double lookaheadConfidenceThreshold;
+
+ /** Signature entry data type */
+ struct SignatureEntry : public TaggedEntry
+ {
+ /** Path signature */
+ signature_t signature;
+ /** Last accessed block within a page */
+ stride_t lastBlock;
+ SignatureEntry() : signature(0), lastBlock(0)
+ {}
+ };
+ /** Signature table */
+ AssociativeSet<SignatureEntry> signatureTable;
+
+ /** A stride entry with its counter */
+ struct PatternStrideEntry
+ {
+ /** stride in a page in blkSize increments */
+ stride_t stride;
+ /** counter value (max value defined by maxCounterValue) */
+ uint8_t counter;
+ PatternStrideEntry() : stride(0), counter(0)
+ {}
+ };
+ /** Pattern entry data type, a set of stride and counter entries */
+ struct PatternEntry : public TaggedEntry
+ {
+ /** group of stides */
+ std::vector<PatternStrideEntry> strideEntries;
+ PatternEntry(size_t num_strides) : strideEntries(num_strides)
+ {}
+
+ /** Reset the entries to their initial values */
+ void reset() override
+ {
+ for (auto &entry : strideEntries) {
+ entry.counter = 0;
+ entry.stride = 0;
+ }
+ }
+
+ /**
+ * Returns the entry with the desired stride
+ * @param stride the stride to find
+ * @result a pointer to the entry, if the stride was found, or nullptr,
+ * if the stride was not found
+ */
+ PatternStrideEntry *findStride(stride_t stride)
+ {
+ PatternStrideEntry *found_entry = nullptr;
+ for (auto &entry : strideEntries) {
+ if (entry.stride == stride) {
+ found_entry = &entry;
+ break;
+ }
+ }
+ return found_entry;
+ }
+
+ /**
+ * Gets the entry with the provided stride, if there is no entry with
+ * the associated stride, it replaces one of them.
+ * @param stride the stride to find
+ * @param max_counter_value maximum value of the confidence counters,
+ * it is used when no strides are found and an entry needs to be
+ * replaced
+ * @result reference to the selected entry
+ */
+ PatternStrideEntry &getStrideEntry(stride_t stride,
+ uint8_t max_counter_value);
+ };
+ /** Pattern table */
+ AssociativeSet<PatternEntry> patternTable;
+
+ /**
+ * Generates a new signature from an existing one and a new stride
+ * @param sig current signature
+ * @param str stride to add to the new signature
+ * @result the new signature
+ */
+ inline signature_t updateSignature(signature_t sig, stride_t str) const {
+ sig <<= signatureShift;
+ sig ^= str;
+ sig &= mask(signatureBits);
+ return sig;
+ }
+
+ /**
+ * Generates an address to be prefetched.
+ * @param ppn page number to prefetch from
+ * @param block block number within the page, this value can be negative,
+ * which means that the block refered is actualy in the previous
+ * page (ppn-1), if the value is greater than (pageBytes/blkSize-1)
+ * then the block refers to a block within the next page (ppn+1)
+ * @param is_secure whether this page is inside the secure memory area
+ * @param addresses if allowed, the address will be added to this vector
+ */
+ void addPrefetch(Addr ppn, stride_t block, bool is_secure,
+ std::vector<AddrPriority> &addresses);
+
+ /**
+ * Obtains the SignatureEntry of the given page, if the page is not found,
+ * it allocates a new one, replacing an existing entry if needed
+ * @param ppn physical page number of the page
+ * @param is_secure whether this page is inside the secure memory area
+ * @param block accessed block within the page
+ * @param miss output, if the entry is not found, this will be set to true
+ * @result a reference to the SignatureEntry
+ */
+ SignatureEntry & getSignatureEntry(Addr ppn, bool is_secure,
+ stride_t block, bool &miss);
+ /**
+ * Obtains the PatternEntry of the given signature, if the signature is
+ * not found, it allocates a new one, replacing an existing entry if needed
+ * @param signature the signature of the desired entry
+ * @result a reference to the PatternEntry
+ */
+ PatternEntry & getPatternEntry(Addr signature);
+
+ /**
+ * Updates the pattern table with the provided signature and stride
+ * @param signature the signature to use to index the pattern table
+ * @param stride the stride to use to index the set of strides of the
+ * pattern table entry
+ */
+ void updatePatternTable(Addr signature, stride_t stride);
+
+ public:
+ SignaturePathPrefetcher(const SignaturePathPrefetcherParams* p);
+ ~SignaturePathPrefetcher() {}
+ void calculatePrefetch(const PrefetchInfo &pfi,
+ std::vector<AddrPriority> &addresses) override;
+};
+
+#endif//__MEM_CACHE_PREFETCH_SIGNATURE_PATH_HH__
