1/**
2 * Copyright (c) 2018 Metempsy Technology Consulting
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions are
7 * met: redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer;
9 * redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution;
12 * neither the name of the copyright holders nor the names of its
13 * contributors may be used to endorse or promote products derived from
14 * this software without specific prior written permission.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
20 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
26 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 *
28 * Authors: Javier Bueno
29 */
30
31#include "mem/cache/prefetch/signature_path.hh"
32
33#include <cassert>
| 1/**
2 * Copyright (c) 2018 Metempsy Technology Consulting
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions are
7 * met: redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer;
9 * redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution;
12 * neither the name of the copyright holders nor the names of its
13 * contributors may be used to endorse or promote products derived from
14 * this software without specific prior written permission.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
20 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
26 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 *
28 * Authors: Javier Bueno
29 */
30
31#include "mem/cache/prefetch/signature_path.hh"
32
33#include <cassert>
|
| 34#include <climits>
|
34
35#include "debug/HWPrefetch.hh"
36#include "mem/cache/prefetch/associative_set_impl.hh"
37#include "params/SignaturePathPrefetcher.hh"
38
39SignaturePathPrefetcher::SignaturePathPrefetcher(
40 const SignaturePathPrefetcherParams *p)
41 : QueuedPrefetcher(p),
42 stridesPerPatternEntry(p->strides_per_pattern_entry),
43 signatureShift(p->signature_shift),
44 signatureBits(p->signature_bits),
| 35
36#include "debug/HWPrefetch.hh"
37#include "mem/cache/prefetch/associative_set_impl.hh"
38#include "params/SignaturePathPrefetcher.hh"
39
40SignaturePathPrefetcher::SignaturePathPrefetcher(
41 const SignaturePathPrefetcherParams *p)
42 : QueuedPrefetcher(p),
43 stridesPerPatternEntry(p->strides_per_pattern_entry),
44 signatureShift(p->signature_shift),
45 signatureBits(p->signature_bits),
|
45 maxCounterValue(p->max_counter_value),
| |
46 prefetchConfidenceThreshold(p->prefetch_confidence_threshold),
47 lookaheadConfidenceThreshold(p->lookahead_confidence_threshold),
48 signatureTable(p->signature_table_assoc, p->signature_table_entries,
49 p->signature_table_indexing_policy,
50 p->signature_table_replacement_policy),
51 patternTable(p->pattern_table_assoc, p->pattern_table_entries,
52 p->pattern_table_indexing_policy,
53 p->pattern_table_replacement_policy,
| 46 prefetchConfidenceThreshold(p->prefetch_confidence_threshold),
47 lookaheadConfidenceThreshold(p->lookahead_confidence_threshold),
48 signatureTable(p->signature_table_assoc, p->signature_table_entries,
49 p->signature_table_indexing_policy,
50 p->signature_table_replacement_policy),
51 patternTable(p->pattern_table_assoc, p->pattern_table_entries,
52 p->pattern_table_indexing_policy,
53 p->pattern_table_replacement_policy,
|
54 PatternEntry(stridesPerPatternEntry))
| 54 PatternEntry(stridesPerPatternEntry, p->num_counter_bits))
|
55{
56 fatal_if(prefetchConfidenceThreshold < 0,
57 "The prefetch confidence threshold must be greater than 0\n");
58 fatal_if(prefetchConfidenceThreshold > 1,
59 "The prefetch confidence threshold must be less than 1\n");
60 fatal_if(lookaheadConfidenceThreshold < 0,
61 "The lookahead confidence threshold must be greater than 0\n");
62 fatal_if(lookaheadConfidenceThreshold > 1,
63 "The lookahead confidence threshold must be less than 1\n");
64}
65
66SignaturePathPrefetcher::PatternStrideEntry &
| 55{
56 fatal_if(prefetchConfidenceThreshold < 0,
57 "The prefetch confidence threshold must be greater than 0\n");
58 fatal_if(prefetchConfidenceThreshold > 1,
59 "The prefetch confidence threshold must be less than 1\n");
60 fatal_if(lookaheadConfidenceThreshold < 0,
61 "The lookahead confidence threshold must be greater than 0\n");
62 fatal_if(lookaheadConfidenceThreshold > 1,
63 "The lookahead confidence threshold must be less than 1\n");
64}
65
66SignaturePathPrefetcher::PatternStrideEntry &
|
67SignaturePathPrefetcher::PatternEntry::getStrideEntry(stride_t stride,
68 uint8_t max_counter_value)
| 67SignaturePathPrefetcher::PatternEntry::getStrideEntry(stride_t stride)
|
69{
70 PatternStrideEntry *pstride_entry = findStride(stride);
71 if (pstride_entry == nullptr) {
72 // Specific replacement algorithm for this table,
73 // pick the entry with the lowest counter value,
74 // then decrease the counter of all entries
75
76 // If all counters have the max value, this will be the pick
77 PatternStrideEntry *victim_pstride_entry = &(strideEntries[0]);
78
| 68{
69 PatternStrideEntry *pstride_entry = findStride(stride);
70 if (pstride_entry == nullptr) {
71 // Specific replacement algorithm for this table,
72 // pick the entry with the lowest counter value,
73 // then decrease the counter of all entries
74
75 // If all counters have the max value, this will be the pick
76 PatternStrideEntry *victim_pstride_entry = &(strideEntries[0]);
77
|
79 uint8_t current_counter = max_counter_value;
| 78 unsigned long current_counter = ULONG_MAX;
|
80 for (auto &entry : strideEntries) {
81 if (entry.counter < current_counter) {
82 victim_pstride_entry = &entry;
83 current_counter = entry.counter;
84 }
| 79 for (auto &entry : strideEntries) {
80 if (entry.counter < current_counter) {
81 victim_pstride_entry = &entry;
82 current_counter = entry.counter;
83 }
|
85 if (entry.counter > 0) {
86 entry.counter -= 1;
87 }
| 84 entry.counter--;
|
88 }
89 pstride_entry = victim_pstride_entry;
| 85 }
86 pstride_entry = victim_pstride_entry;
|
90 pstride_entry->counter = 0;
| 87 pstride_entry->counter.reset();
|
91 pstride_entry->stride = stride;
92 }
93 return *pstride_entry;
94}
95
96void
97SignaturePathPrefetcher::addPrefetch(Addr ppn, stride_t last_block,
98 stride_t delta, double path_confidence, signature_t signature,
99 bool is_secure, std::vector<AddrPriority> &addresses)
100{
101 stride_t block = last_block + delta;
102
103 Addr pf_ppn;
104 stride_t pf_block;
105 if (block < 0) {
106 stride_t num_cross_pages = 1 + (-block) / (pageBytes/blkSize);
107 if (num_cross_pages > ppn) {
108 // target address smaller than page 0, ignore this request;
109 return;
110 }
111 pf_ppn = ppn - num_cross_pages;
112 pf_block = block + (pageBytes/blkSize) * num_cross_pages;
113 handlePageCrossingLookahead(signature, last_block, delta,
114 path_confidence);
115 } else if (block >= (pageBytes/blkSize)) {
116 stride_t num_cross_pages = block / (pageBytes/blkSize);
117 if (MaxAddr/pageBytes < (ppn + num_cross_pages)) {
118 // target address goes beyond MaxAddr, ignore this request;
119 return;
120 }
121 pf_ppn = ppn + num_cross_pages;
122 pf_block = block - (pageBytes/blkSize) * num_cross_pages;
123 handlePageCrossingLookahead(signature, last_block, delta,
124 path_confidence);
125 } else {
126 pf_ppn = ppn;
127 pf_block = block;
128 }
129
130 Addr new_addr = pf_ppn * pageBytes;
131 new_addr += pf_block * (Addr)blkSize;
132
133 DPRINTF(HWPrefetch, "Queuing prefetch to %#x.\n", new_addr);
134 addresses.push_back(AddrPriority(new_addr, 0));
135}
136
137void
138SignaturePathPrefetcher::handleSignatureTableMiss(stride_t current_block,
139 signature_t &new_signature, double &new_conf, stride_t &new_stride)
140{
141 new_signature = current_block;
142 new_conf = 1.0;
143 new_stride = current_block;
144}
145
146void
147SignaturePathPrefetcher::increasePatternEntryCounter(
148 PatternEntry &pattern_entry, PatternStrideEntry &pstride_entry)
149{
| 88 pstride_entry->stride = stride;
89 }
90 return *pstride_entry;
91}
92
93void
94SignaturePathPrefetcher::addPrefetch(Addr ppn, stride_t last_block,
95 stride_t delta, double path_confidence, signature_t signature,
96 bool is_secure, std::vector<AddrPriority> &addresses)
97{
98 stride_t block = last_block + delta;
99
100 Addr pf_ppn;
101 stride_t pf_block;
102 if (block < 0) {
103 stride_t num_cross_pages = 1 + (-block) / (pageBytes/blkSize);
104 if (num_cross_pages > ppn) {
105 // target address smaller than page 0, ignore this request;
106 return;
107 }
108 pf_ppn = ppn - num_cross_pages;
109 pf_block = block + (pageBytes/blkSize) * num_cross_pages;
110 handlePageCrossingLookahead(signature, last_block, delta,
111 path_confidence);
112 } else if (block >= (pageBytes/blkSize)) {
113 stride_t num_cross_pages = block / (pageBytes/blkSize);
114 if (MaxAddr/pageBytes < (ppn + num_cross_pages)) {
115 // target address goes beyond MaxAddr, ignore this request;
116 return;
117 }
118 pf_ppn = ppn + num_cross_pages;
119 pf_block = block - (pageBytes/blkSize) * num_cross_pages;
120 handlePageCrossingLookahead(signature, last_block, delta,
121 path_confidence);
122 } else {
123 pf_ppn = ppn;
124 pf_block = block;
125 }
126
127 Addr new_addr = pf_ppn * pageBytes;
128 new_addr += pf_block * (Addr)blkSize;
129
130 DPRINTF(HWPrefetch, "Queuing prefetch to %#x.\n", new_addr);
131 addresses.push_back(AddrPriority(new_addr, 0));
132}
133
134void
135SignaturePathPrefetcher::handleSignatureTableMiss(stride_t current_block,
136 signature_t &new_signature, double &new_conf, stride_t &new_stride)
137{
138 new_signature = current_block;
139 new_conf = 1.0;
140 new_stride = current_block;
141}
142
143void
144SignaturePathPrefetcher::increasePatternEntryCounter(
145 PatternEntry &pattern_entry, PatternStrideEntry &pstride_entry)
146{
|
150 if (pstride_entry.counter < maxCounterValue) {
151 pstride_entry.counter += 1;
152 }
| 147 pstride_entry.counter++;
|
153}
154
155void
156SignaturePathPrefetcher::updatePatternTable(Addr signature, stride_t stride)
157{
158 assert(stride != 0);
159 // The pattern table is indexed by signatures
160 PatternEntry &p_entry = getPatternEntry(signature);
| 148}
149
150void
151SignaturePathPrefetcher::updatePatternTable(Addr signature, stride_t stride)
152{
153 assert(stride != 0);
154 // The pattern table is indexed by signatures
155 PatternEntry &p_entry = getPatternEntry(signature);
|
161 PatternStrideEntry &ps_entry = p_entry.getStrideEntry(stride,
162 maxCounterValue);
| 156 PatternStrideEntry &ps_entry = p_entry.getStrideEntry(stride);
|
163 increasePatternEntryCounter(p_entry, ps_entry);
164}
165
166SignaturePathPrefetcher::SignatureEntry &
167SignaturePathPrefetcher::getSignatureEntry(Addr ppn, bool is_secure,
168 stride_t block, bool &miss, stride_t &stride,
169 double &initial_confidence)
170{
171 SignatureEntry* signature_entry = signatureTable.findEntry(ppn, is_secure);
172 if (signature_entry != nullptr) {
173 signatureTable.accessEntry(signature_entry);
174 miss = false;
175 stride = block - signature_entry->lastBlock;
176 } else {
177 signature_entry = signatureTable.findVictim(ppn);
178 assert(signature_entry != nullptr);
179
180 // Sets signature_entry->signature, initial_confidence, and stride
181 handleSignatureTableMiss(block, signature_entry->signature,
182 initial_confidence, stride);
183
184 signatureTable.insertEntry(ppn, is_secure, signature_entry);
185 miss = true;
186 }
187 signature_entry->lastBlock = block;
188 return *signature_entry;
189}
190
191SignaturePathPrefetcher::PatternEntry &
192SignaturePathPrefetcher::getPatternEntry(Addr signature)
193{
194 PatternEntry* pattern_entry = patternTable.findEntry(signature, false);
195 if (pattern_entry != nullptr) {
196 // Signature found
197 patternTable.accessEntry(pattern_entry);
198 } else {
199 // Signature not found
200 pattern_entry = patternTable.findVictim(signature);
201 assert(pattern_entry != nullptr);
202
203 patternTable.insertEntry(signature, false, pattern_entry);
204 }
205 return *pattern_entry;
206}
207
208double
209SignaturePathPrefetcher::calculatePrefetchConfidence(PatternEntry const &sig,
210 PatternStrideEntry const &entry) const
211{
| 157 increasePatternEntryCounter(p_entry, ps_entry);
158}
159
160SignaturePathPrefetcher::SignatureEntry &
161SignaturePathPrefetcher::getSignatureEntry(Addr ppn, bool is_secure,
162 stride_t block, bool &miss, stride_t &stride,
163 double &initial_confidence)
164{
165 SignatureEntry* signature_entry = signatureTable.findEntry(ppn, is_secure);
166 if (signature_entry != nullptr) {
167 signatureTable.accessEntry(signature_entry);
168 miss = false;
169 stride = block - signature_entry->lastBlock;
170 } else {
171 signature_entry = signatureTable.findVictim(ppn);
172 assert(signature_entry != nullptr);
173
174 // Sets signature_entry->signature, initial_confidence, and stride
175 handleSignatureTableMiss(block, signature_entry->signature,
176 initial_confidence, stride);
177
178 signatureTable.insertEntry(ppn, is_secure, signature_entry);
179 miss = true;
180 }
181 signature_entry->lastBlock = block;
182 return *signature_entry;
183}
184
185SignaturePathPrefetcher::PatternEntry &
186SignaturePathPrefetcher::getPatternEntry(Addr signature)
187{
188 PatternEntry* pattern_entry = patternTable.findEntry(signature, false);
189 if (pattern_entry != nullptr) {
190 // Signature found
191 patternTable.accessEntry(pattern_entry);
192 } else {
193 // Signature not found
194 pattern_entry = patternTable.findVictim(signature);
195 assert(pattern_entry != nullptr);
196
197 patternTable.insertEntry(signature, false, pattern_entry);
198 }
199 return *pattern_entry;
200}
201
202double
203SignaturePathPrefetcher::calculatePrefetchConfidence(PatternEntry const &sig,
204 PatternStrideEntry const &entry) const
205{
|
212 return ((double) entry.counter) / maxCounterValue;
| 206 return entry.counter.calcSaturation();
|
213}
214
215double
216SignaturePathPrefetcher::calculateLookaheadConfidence(PatternEntry const &sig,
217 PatternStrideEntry const &lookahead) const
218{
| 207}
208
209double
210SignaturePathPrefetcher::calculateLookaheadConfidence(PatternEntry const &sig,
211 PatternStrideEntry const &lookahead) const
212{
|
219 double lookahead_confidence;
220 if (lookahead.counter == maxCounterValue) {
| 213 double lookahead_confidence = lookahead.counter.calcSaturation();
214 if (lookahead_confidence > 0.95) {
|
221 /**
222 * maximum confidence is 0.95, guaranteeing that
223 * current confidence will eventually fall beyond
224 * the threshold
225 */
226 lookahead_confidence = 0.95;
| 215 /**
216 * maximum confidence is 0.95, guaranteeing that
217 * current confidence will eventually fall beyond
218 * the threshold
219 */
220 lookahead_confidence = 0.95;
|
227 } else {
228 lookahead_confidence = ((double) lookahead.counter / maxCounterValue);
| |
229 }
230 return lookahead_confidence;
231}
232
233void
234SignaturePathPrefetcher::calculatePrefetch(const PrefetchInfo &pfi,
235 std::vector<AddrPriority> &addresses)
236{
237 Addr request_addr = pfi.getAddr();
238 Addr ppn = request_addr / pageBytes;
239 stride_t current_block = (request_addr % pageBytes) / blkSize;
240 stride_t stride;
241 bool is_secure = pfi.isSecure();
242 double initial_confidence = 1.0;
243
244 // Get the SignatureEntry of this page to:
245 // - compute the current stride
246 // - obtain the current signature of accesses
247 bool miss;
248 SignatureEntry &signature_entry = getSignatureEntry(ppn, is_secure,
249 current_block, miss, stride, initial_confidence);
250
251 if (miss) {
252 // No history for this page, can't continue
253 return;
254 }
255
256 if (stride == 0) {
257 // Can't continue with a stride 0
258 return;
259 }
260
261 // Update the confidence of the current signature
262 updatePatternTable(signature_entry.signature, stride);
263
264 // Update the current SignatureEntry signature
265 signature_entry.signature =
266 updateSignature(signature_entry.signature, stride);
267
268 signature_t current_signature = signature_entry.signature;
269 double current_confidence = initial_confidence;
270 stride_t current_stride = signature_entry.lastBlock;
271
272 // Look for prefetch candidates while the current path confidence is
273 // high enough
274 while (current_confidence > lookaheadConfidenceThreshold) {
275 // With the updated signature, attempt to generate prefetches
276 // - search the PatternTable and select all entries with enough
277 // confidence, these are prefetch candidates
278 // - select the entry with the highest counter as the "lookahead"
279 PatternEntry *current_pattern_entry =
280 patternTable.findEntry(current_signature, false);
281 PatternStrideEntry const *lookahead = nullptr;
282 if (current_pattern_entry != nullptr) {
| 221 }
222 return lookahead_confidence;
223}
224
225void
226SignaturePathPrefetcher::calculatePrefetch(const PrefetchInfo &pfi,
227 std::vector<AddrPriority> &addresses)
228{
229 Addr request_addr = pfi.getAddr();
230 Addr ppn = request_addr / pageBytes;
231 stride_t current_block = (request_addr % pageBytes) / blkSize;
232 stride_t stride;
233 bool is_secure = pfi.isSecure();
234 double initial_confidence = 1.0;
235
236 // Get the SignatureEntry of this page to:
237 // - compute the current stride
238 // - obtain the current signature of accesses
239 bool miss;
240 SignatureEntry &signature_entry = getSignatureEntry(ppn, is_secure,
241 current_block, miss, stride, initial_confidence);
242
243 if (miss) {
244 // No history for this page, can't continue
245 return;
246 }
247
248 if (stride == 0) {
249 // Can't continue with a stride 0
250 return;
251 }
252
253 // Update the confidence of the current signature
254 updatePatternTable(signature_entry.signature, stride);
255
256 // Update the current SignatureEntry signature
257 signature_entry.signature =
258 updateSignature(signature_entry.signature, stride);
259
260 signature_t current_signature = signature_entry.signature;
261 double current_confidence = initial_confidence;
262 stride_t current_stride = signature_entry.lastBlock;
263
264 // Look for prefetch candidates while the current path confidence is
265 // high enough
266 while (current_confidence > lookaheadConfidenceThreshold) {
267 // With the updated signature, attempt to generate prefetches
268 // - search the PatternTable and select all entries with enough
269 // confidence, these are prefetch candidates
270 // - select the entry with the highest counter as the "lookahead"
271 PatternEntry *current_pattern_entry =
272 patternTable.findEntry(current_signature, false);
273 PatternStrideEntry const *lookahead = nullptr;
274 if (current_pattern_entry != nullptr) {
|
283 uint8_t max_counter = 0;
| 275 unsigned long max_counter = 0;
|
284 for (auto const &entry : current_pattern_entry->strideEntries) {
285 //select the entry with the maximum counter value as lookahead
286 if (max_counter < entry.counter) {
287 max_counter = entry.counter;
288 lookahead = &entry;
289 }
290 double prefetch_confidence =
291 calculatePrefetchConfidence(*current_pattern_entry, entry);
292
293 if (prefetch_confidence >= prefetchConfidenceThreshold) {
294 assert(entry.stride != 0);
295 //prefetch candidate
296 addPrefetch(ppn, current_stride, entry.stride,
297 current_confidence, current_signature,
298 is_secure, addresses);
299 }
300 }
301 }
302
303 if (lookahead != nullptr) {
304 current_confidence *= calculateLookaheadConfidence(
305 *current_pattern_entry, *lookahead);
306 current_signature =
307 updateSignature(current_signature, lookahead->stride);
308 current_stride += lookahead->stride;
309 } else {
310 current_confidence = 0.0;
311 }
312 }
313
314 auxiliaryPrefetcher(ppn, current_block, is_secure, addresses);
315}
316
317void
318SignaturePathPrefetcher::auxiliaryPrefetcher(Addr ppn, stride_t current_block,
319 bool is_secure, std::vector<AddrPriority> &addresses)
320{
321 if (addresses.empty()) {
322 // Enable the next line prefetcher if no prefetch candidates are found
323 addPrefetch(ppn, current_block, 1, 0.0 /* unused*/, 0 /* unused */,
324 is_secure, addresses);
325 }
326}
327
328SignaturePathPrefetcher*
329SignaturePathPrefetcherParams::create()
330{
331 return new SignaturePathPrefetcher(this);
332}
| 276 for (auto const &entry : current_pattern_entry->strideEntries) {
277 //select the entry with the maximum counter value as lookahead
278 if (max_counter < entry.counter) {
279 max_counter = entry.counter;
280 lookahead = &entry;
281 }
282 double prefetch_confidence =
283 calculatePrefetchConfidence(*current_pattern_entry, entry);
284
285 if (prefetch_confidence >= prefetchConfidenceThreshold) {
286 assert(entry.stride != 0);
287 //prefetch candidate
288 addPrefetch(ppn, current_stride, entry.stride,
289 current_confidence, current_signature,
290 is_secure, addresses);
291 }
292 }
293 }
294
295 if (lookahead != nullptr) {
296 current_confidence *= calculateLookaheadConfidence(
297 *current_pattern_entry, *lookahead);
298 current_signature =
299 updateSignature(current_signature, lookahead->stride);
300 current_stride += lookahead->stride;
301 } else {
302 current_confidence = 0.0;
303 }
304 }
305
306 auxiliaryPrefetcher(ppn, current_block, is_secure, addresses);
307}
308
309void
310SignaturePathPrefetcher::auxiliaryPrefetcher(Addr ppn, stride_t current_block,
311 bool is_secure, std::vector<AddrPriority> &addresses)
312{
313 if (addresses.empty()) {
314 // Enable the next line prefetcher if no prefetch candidates are found
315 addPrefetch(ppn, current_block, 1, 0.0 /* unused*/, 0 /* unused */,
316 is_secure, addresses);
317 }
318}
319
320SignaturePathPrefetcher*
321SignaturePathPrefetcherParams::create()
322{
323 return new SignaturePathPrefetcher(this);
324}
|