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 /**
32 * Implementation of the Signature Path Prefetcher
33 *
34 * References:
35 * Lookahead prefetching with signature path
36 * J Kim, PV Gratz, ALN Reddy
37 * The 2nd Data Prefetching Championship (DPC2)
38 * The filter feature described in the paper is not implemented, as it
39 * redundant prefetches are dropped by the cache.
40 */
41
42#ifndef __MEM_CACHE_PREFETCH_SIGNATURE_PATH_HH__
43#define __MEM_CACHE_PREFETCH_SIGNATURE_PATH_HH__
44
45#include "mem/cache/prefetch/associative_set.hh"
46#include "mem/cache/prefetch/queued.hh"
47#include "mem/packet.hh"
48
49struct SignaturePathPrefetcherParams;
50
51class SignaturePathPrefetcher : public QueuedPrefetcher
52{
| 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 /**
32 * Implementation of the Signature Path Prefetcher
33 *
34 * References:
35 * Lookahead prefetching with signature path
36 * J Kim, PV Gratz, ALN Reddy
37 * The 2nd Data Prefetching Championship (DPC2)
38 * The filter feature described in the paper is not implemented, as it
39 * redundant prefetches are dropped by the cache.
40 */
41
42#ifndef __MEM_CACHE_PREFETCH_SIGNATURE_PATH_HH__
43#define __MEM_CACHE_PREFETCH_SIGNATURE_PATH_HH__
44
45#include "mem/cache/prefetch/associative_set.hh"
46#include "mem/cache/prefetch/queued.hh"
47#include "mem/packet.hh"
48
49struct SignaturePathPrefetcherParams;
50
51class SignaturePathPrefetcher : public QueuedPrefetcher
52{
|
| 53 protected:
|
53 /** Signature type */
54 typedef uint16_t signature_t;
55 /** Stride type */
56 typedef int16_t stride_t;
57
58 /** Number of strides stored in each pattern entry */
59 const unsigned stridesPerPatternEntry;
60 /** Number of bits to shift when generating a new signature */
61 const uint8_t signatureShift;
62 /** Size of the signature, in bits */
63 const signature_t signatureBits;
64 /** Maximum pattern entries counter value */
65 const uint8_t maxCounterValue;
66 /** Minimum confidence to issue a prefetch */
67 const double prefetchConfidenceThreshold;
68 /** Minimum confidence to keep navigating lookahead entries */
69 const double lookaheadConfidenceThreshold;
70
71 /** Signature entry data type */
72 struct SignatureEntry : public TaggedEntry
73 {
74 /** Path signature */
75 signature_t signature;
76 /** Last accessed block within a page */
77 stride_t lastBlock;
78 SignatureEntry() : signature(0), lastBlock(0)
79 {}
80 };
81 /** Signature table */
82 AssociativeSet<SignatureEntry> signatureTable;
83
84 /** A stride entry with its counter */
85 struct PatternStrideEntry
86 {
87 /** stride in a page in blkSize increments */
88 stride_t stride;
89 /** counter value (max value defined by maxCounterValue) */
90 uint8_t counter;
91 PatternStrideEntry() : stride(0), counter(0)
92 {}
93 };
94 /** Pattern entry data type, a set of stride and counter entries */
95 struct PatternEntry : public TaggedEntry
96 {
97 /** group of stides */
98 std::vector<PatternStrideEntry> strideEntries;
| 54 /** Signature type */
55 typedef uint16_t signature_t;
56 /** Stride type */
57 typedef int16_t stride_t;
58
59 /** Number of strides stored in each pattern entry */
60 const unsigned stridesPerPatternEntry;
61 /** Number of bits to shift when generating a new signature */
62 const uint8_t signatureShift;
63 /** Size of the signature, in bits */
64 const signature_t signatureBits;
65 /** Maximum pattern entries counter value */
66 const uint8_t maxCounterValue;
67 /** Minimum confidence to issue a prefetch */
68 const double prefetchConfidenceThreshold;
69 /** Minimum confidence to keep navigating lookahead entries */
70 const double lookaheadConfidenceThreshold;
71
72 /** Signature entry data type */
73 struct SignatureEntry : public TaggedEntry
74 {
75 /** Path signature */
76 signature_t signature;
77 /** Last accessed block within a page */
78 stride_t lastBlock;
79 SignatureEntry() : signature(0), lastBlock(0)
80 {}
81 };
82 /** Signature table */
83 AssociativeSet<SignatureEntry> signatureTable;
84
85 /** A stride entry with its counter */
86 struct PatternStrideEntry
87 {
88 /** stride in a page in blkSize increments */
89 stride_t stride;
90 /** counter value (max value defined by maxCounterValue) */
91 uint8_t counter;
92 PatternStrideEntry() : stride(0), counter(0)
93 {}
94 };
95 /** Pattern entry data type, a set of stride and counter entries */
96 struct PatternEntry : public TaggedEntry
97 {
98 /** group of stides */
99 std::vector<PatternStrideEntry> strideEntries;
|
99 PatternEntry(size_t num_strides) : strideEntries(num_strides)
| 100 /** use counter, used by SPPv2 */
101 uint8_t counter;
102 PatternEntry(size_t num_strides) : strideEntries(num_strides),
103 counter(0)
|
100 {}
101
102 /** Reset the entries to their initial values */
103 void reset() override
104 {
105 for (auto &entry : strideEntries) {
106 entry.counter = 0;
107 entry.stride = 0;
108 }
| 104 {}
105
106 /** Reset the entries to their initial values */
107 void reset() override
108 {
109 for (auto &entry : strideEntries) {
110 entry.counter = 0;
111 entry.stride = 0;
112 }
|
| 113 counter = 0;
|
109 }
110
111 /**
112 * Returns the entry with the desired stride
113 * @param stride the stride to find
114 * @result a pointer to the entry, if the stride was found, or nullptr,
115 * if the stride was not found
116 */
117 PatternStrideEntry *findStride(stride_t stride)
118 {
119 PatternStrideEntry *found_entry = nullptr;
120 for (auto &entry : strideEntries) {
121 if (entry.stride == stride) {
122 found_entry = &entry;
123 break;
124 }
125 }
126 return found_entry;
127 }
128
129 /**
130 * Gets the entry with the provided stride, if there is no entry with
131 * the associated stride, it replaces one of them.
132 * @param stride the stride to find
133 * @param max_counter_value maximum value of the confidence counters,
134 * it is used when no strides are found and an entry needs to be
135 * replaced
136 * @result reference to the selected entry
137 */
138 PatternStrideEntry &getStrideEntry(stride_t stride,
139 uint8_t max_counter_value);
140 };
141 /** Pattern table */
142 AssociativeSet<PatternEntry> patternTable;
143
144 /**
145 * Generates a new signature from an existing one and a new stride
146 * @param sig current signature
147 * @param str stride to add to the new signature
148 * @result the new signature
149 */
150 inline signature_t updateSignature(signature_t sig, stride_t str) const {
151 sig <<= signatureShift;
152 sig ^= str;
153 sig &= mask(signatureBits);
154 return sig;
155 }
156
157 /**
158 * Generates an address to be prefetched.
159 * @param ppn page number to prefetch from
| 114 }
115
116 /**
117 * Returns the entry with the desired stride
118 * @param stride the stride to find
119 * @result a pointer to the entry, if the stride was found, or nullptr,
120 * if the stride was not found
121 */
122 PatternStrideEntry *findStride(stride_t stride)
123 {
124 PatternStrideEntry *found_entry = nullptr;
125 for (auto &entry : strideEntries) {
126 if (entry.stride == stride) {
127 found_entry = &entry;
128 break;
129 }
130 }
131 return found_entry;
132 }
133
134 /**
135 * Gets the entry with the provided stride, if there is no entry with
136 * the associated stride, it replaces one of them.
137 * @param stride the stride to find
138 * @param max_counter_value maximum value of the confidence counters,
139 * it is used when no strides are found and an entry needs to be
140 * replaced
141 * @result reference to the selected entry
142 */
143 PatternStrideEntry &getStrideEntry(stride_t stride,
144 uint8_t max_counter_value);
145 };
146 /** Pattern table */
147 AssociativeSet<PatternEntry> patternTable;
148
149 /**
150 * Generates a new signature from an existing one and a new stride
151 * @param sig current signature
152 * @param str stride to add to the new signature
153 * @result the new signature
154 */
155 inline signature_t updateSignature(signature_t sig, stride_t str) const {
156 sig <<= signatureShift;
157 sig ^= str;
158 sig &= mask(signatureBits);
159 return sig;
160 }
161
162 /**
163 * Generates an address to be prefetched.
164 * @param ppn page number to prefetch from
|
160 * @param block block number within the page, this value can be negative,
161 * which means that the block refered is actualy in the previous
162 * page (ppn-1), if the value is greater than (pageBytes/blkSize-1)
163 * then the block refers to a block within the next page (ppn+1)
| 165 * @param last_block last accessed block within the page ppn
166 * @param delta difference, in number of blocks, from the last_block
167 * accessed to the block to prefetch. The block to prefetch is
168 * computed by this formula:
169 * ppn * pageBytes + (last_block + delta) * blkSize
170 * This value can be negative.
171 * @param path_confidence the confidence factor of this prefetch
172 * @param signature the current path signature
|
164 * @param is_secure whether this page is inside the secure memory area
| 173 * @param is_secure whether this page is inside the secure memory area
|
165 * @param addresses if allowed, the address will be added to this vector
| 174 * @param addresses addresses to prefetch will be added to this vector
|
166 */
| 175 */
|
167 void addPrefetch(Addr ppn, stride_t block, bool is_secure,
168 std::vector<AddrPriority> &addresses);
| 176 void addPrefetch(Addr ppn, stride_t last_block, stride_t delta,
177 double path_confidence, signature_t signature,
178 bool is_secure,
179 std::vector<AddrPriority> &addresses);
|
169
170 /**
171 * Obtains the SignatureEntry of the given page, if the page is not found,
172 * it allocates a new one, replacing an existing entry if needed
| 180
181 /**
182 * Obtains the SignatureEntry of the given page, if the page is not found,
183 * it allocates a new one, replacing an existing entry if needed
|
| 184 * It also provides the stride of the current block and the initial
185 * path confidence of the corresponding entry
|
173 * @param ppn physical page number of the page
174 * @param is_secure whether this page is inside the secure memory area
175 * @param block accessed block within the page
| 186 * @param ppn physical page number of the page
187 * @param is_secure whether this page is inside the secure memory area
188 * @param block accessed block within the page
|
176 * @param miss output, if the entry is not found, this will be set to true
| 189 * @param miss if the entry is not found, this will be set to true
190 * @param stride set to the computed stride
191 * @param initial_confidence set to the initial confidence value
|
177 * @result a reference to the SignatureEntry
178 */
| 192 * @result a reference to the SignatureEntry
193 */
|
179 SignatureEntry & getSignatureEntry(Addr ppn, bool is_secure,
180 stride_t block, bool &miss);
| 194 SignatureEntry &getSignatureEntry(Addr ppn, bool is_secure, stride_t block,
195 bool &miss, stride_t &stride, double &initial_confidence);
|
181 /**
182 * Obtains the PatternEntry of the given signature, if the signature is
183 * not found, it allocates a new one, replacing an existing entry if needed
184 * @param signature the signature of the desired entry
185 * @result a reference to the PatternEntry
186 */
| 196 /**
197 * Obtains the PatternEntry of the given signature, if the signature is
198 * not found, it allocates a new one, replacing an existing entry if needed
199 * @param signature the signature of the desired entry
200 * @result a reference to the PatternEntry
201 */
|
187 PatternEntry & getPatternEntry(Addr signature);
| 202 PatternEntry& getPatternEntry(Addr signature);
|
188
189 /**
190 * Updates the pattern table with the provided signature and stride
191 * @param signature the signature to use to index the pattern table
192 * @param stride the stride to use to index the set of strides of the
193 * pattern table entry
194 */
195 void updatePatternTable(Addr signature, stride_t stride);
196
| 203
204 /**
205 * Updates the pattern table with the provided signature and stride
206 * @param signature the signature to use to index the pattern table
207 * @param stride the stride to use to index the set of strides of the
208 * pattern table entry
209 */
210 void updatePatternTable(Addr signature, stride_t stride);
211
|
| 212 /**
213 * Computes the lookahead path confidence of the provided pattern entry
214 * @param sig the PatternEntry to use
215 * @param lookahead PatternStrideEntry within the provided PatternEntry
216 * @return the computed confidence factor
217 */
218 virtual double calculateLookaheadConfidence(PatternEntry const &sig,
219 PatternStrideEntry const &lookahead) const;
220
221 /**
222 * Computes the prefetch confidence of the provided pattern entry
223 * @param sig the PatternEntry to use
224 * @param entry PatternStrideEntry within the provided PatternEntry
225 * @return the computed confidence factor
226 */
227 virtual double calculatePrefetchConfidence(PatternEntry const &sig,
228 PatternStrideEntry const &entry) const;
229
230 /**
231 * Increases the counter of a given PatternEntry/PatternStrideEntry
232 * @param pattern_entry the corresponding PatternEntry
233 * @param pstride_entry the PatternStrideEntry within the PatternEntry
234 */
235 virtual void increasePatternEntryCounter(PatternEntry &pattern_entry,
236 PatternStrideEntry &pstride_entry);
237
238 /**
239 * Whenever a new SignatureEntry is allocated, it computes the new
240 * signature to be used with the new entry, the resulting stride and the
241 * initial path confidence of the new entry.
242 * @param current_block accessed block within the page of the associated
243 entry
244 * @param new_signature new signature of the allocated entry
245 * @param new_conf the initial path confidence of this entry
246 * @param new_stride the resulting current stride
247 */
248 virtual void handleSignatureTableMiss(stride_t current_block,
249 signature_t &new_signature, double &new_conf,
250 stride_t &new_stride);
251
252 /**
253 * Auxiliar prefetch mechanism used at the end of calculatePrefetch.
254 * This prefetcher uses this to activate the next line prefetcher if
255 * no prefetch candidates have been found.
256 * @param ppn physical page number of the current accessed page
257 * @param current_block last accessed block within the page ppn
258 * @param is_secure whether this page is inside the secure memory area
259 * @param addresses the addresses to be prefetched are added to this vector
260 * @param updated_filter_entries set of addresses containing these that
261 * their filter has been updated, if this call updates a new entry
262 */
263 virtual void auxiliaryPrefetcher(Addr ppn, stride_t current_block,
264 bool is_secure, std::vector<AddrPriority> &addresses);
265
266 /**
267 * Handles the situation when the lookahead process has crossed the
268 * boundaries of the current page. This is not fully described in the
269 * paper that was used to implement this code, however, the article
270 * describing the upgraded version of this prefetcher provides some
271 * details. For this prefetcher, there are no specific actions to be
272 * done.
273 * @param signature the lookahead signature that crossed the page
274 * @param delta the current stride that caused it
275 * @param last_offset the last accessed block within the page
276 * @param path_confidence the path confidence at the moment of crossing
277 */
278 virtual void handlePageCrossingLookahead(signature_t signature,
279 stride_t last_offset, stride_t delta, double path_confidence) {
280 }
281
|
197 public:
198 SignaturePathPrefetcher(const SignaturePathPrefetcherParams* p);
199 ~SignaturePathPrefetcher() {}
200 void calculatePrefetch(const PrefetchInfo &pfi,
201 std::vector<AddrPriority> &addresses) override;
202};
203
204#endif//__MEM_CACHE_PREFETCH_SIGNATURE_PATH_HH__
| 282 public:
283 SignaturePathPrefetcher(const SignaturePathPrefetcherParams* p);
284 ~SignaturePathPrefetcher() {}
285 void calculatePrefetch(const PrefetchInfo &pfi,
286 std::vector<AddrPriority> &addresses) override;
287};
288
289#endif//__MEM_CACHE_PREFETCH_SIGNATURE_PATH_HH__
|