access_map_pattern_matching.cc revision 13832:79e439e69d9b 
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/access_map_pattern_matching.hh"
32
33#include "debug/HWPrefetch.hh"
34#include "mem/cache/prefetch/associative_set_impl.hh"
35#include "params/AMPMPrefetcher.hh"
36#include "params/AccessMapPatternMatching.hh"
37
38AccessMapPatternMatching::AccessMapPatternMatching(
39    const AccessMapPatternMatchingParams *p)
40    : ClockedObject(p), blkSize(p->block_size), limitStride(p->limit_stride),
41      startDegree(p->start_degree), hotZoneSize(p->hot_zone_size),
42      highCoverageThreshold(p->high_coverage_threshold),
43      lowCoverageThreshold(p->low_coverage_threshold),
44      highAccuracyThreshold(p->high_accuracy_threshold),
45      lowAccuracyThreshold(p->low_accuracy_threshold),
46      highCacheHitThreshold(p->high_cache_hit_threshold),
47      lowCacheHitThreshold(p->low_cache_hit_threshold),
48      epochCycles(p->epoch_cycles),
49      offChipMemoryLatency(p->offchip_memory_latency),
50      accessMapTable(p->access_map_table_assoc, p->access_map_table_entries,
51                     p->access_map_table_indexing_policy,
52                     p->access_map_table_replacement_policy,
53                     AccessMapEntry(hotZoneSize / blkSize)),
54      numGoodPrefetches(0), numTotalPrefetches(0), numRawCacheMisses(0),
55      numRawCacheHits(0), degree(startDegree), usefulDegree(startDegree),
56      epochEvent([this]{ processEpochEvent(); }, name())
57{
58    fatal_if(!isPowerOf2(hotZoneSize),
59        "the hot zone size must be a power of 2");
60}
61
62void
63AccessMapPatternMatching::startup()
64{
65    schedule(epochEvent, clockEdge(epochCycles));
66}
67
68void
69AccessMapPatternMatching::processEpochEvent()
70{
71    schedule(epochEvent, clockEdge(epochCycles));
72    double prefetch_accuracy =
73        ((double) numGoodPrefetches) / ((double) numTotalPrefetches);
74    double prefetch_coverage =
75        ((double) numGoodPrefetches) / ((double) numRawCacheMisses);
76    double cache_hit_ratio = ((double) numRawCacheHits) /
77        ((double) (numRawCacheHits + numRawCacheMisses));
78    double num_requests = (double) (numRawCacheMisses - numGoodPrefetches +
79        numTotalPrefetches);
80    double memory_bandwidth = num_requests * offChipMemoryLatency /
81        clockEdge(epochCycles);
82
83    if (prefetch_coverage > highCoverageThreshold &&
84        (prefetch_accuracy > highAccuracyThreshold ||
85        cache_hit_ratio < lowCacheHitThreshold)) {
86        usefulDegree += 1;
87    } else if ((prefetch_coverage < lowCoverageThreshold &&
88               (prefetch_accuracy < lowAccuracyThreshold ||
89                cache_hit_ratio > highCacheHitThreshold)) ||
90               (prefetch_accuracy < lowAccuracyThreshold &&
91                cache_hit_ratio > highCacheHitThreshold)) {
92        usefulDegree -= 1;
93    }
94    degree = std::min((unsigned) memory_bandwidth, usefulDegree);
95    // reset epoch stats
96    numGoodPrefetches = 0.0;
97    numTotalPrefetches = 0.0;
98    numRawCacheMisses = 0.0;
99    numRawCacheHits = 0.0;
100}
101
102AccessMapPatternMatching::AccessMapEntry *
103AccessMapPatternMatching::getAccessMapEntry(Addr am_addr,
104                bool is_secure)
105{
106    AccessMapEntry *am_entry = accessMapTable.findEntry(am_addr, is_secure);
107    if (am_entry != nullptr) {
108        accessMapTable.accessEntry(am_entry);
109    } else {
110        am_entry = accessMapTable.findVictim(am_addr);
111        assert(am_entry != nullptr);
112
113        accessMapTable.insertEntry(am_addr, is_secure, am_entry);
114    }
115    return am_entry;
116}
117
118void
119AccessMapPatternMatching::setEntryState(AccessMapEntry &entry,
120    Addr block, enum AccessMapState state)
121{
122    enum AccessMapState old = entry.states[block];
123    entry.states[block] = state;
124
125    //do not update stats when initializing
126    if (state == AM_INIT) return;
127
128    switch (old) {
129        case AM_INIT:
130            if (state == AM_PREFETCH) {
131                numTotalPrefetches += 1;
132            } else if (state == AM_ACCESS) {
133                numRawCacheMisses += 1;
134            }
135            break;
136        case AM_PREFETCH:
137            if (state == AM_ACCESS) {
138                numGoodPrefetches += 1;
139                numRawCacheMisses += 1;
140            }
141            break;
142        case AM_ACCESS:
143            if (state == AM_ACCESS) {
144                numRawCacheHits += 1;
145            }
146            break;
147        default:
148            panic("Impossible path\n");
149            break;
150    }
151}
152
153void
154AccessMapPatternMatching::calculatePrefetch(
155    const BasePrefetcher::PrefetchInfo &pfi,
156    std::vector<QueuedPrefetcher::AddrPriority> &addresses)
157{
158    assert(addresses.empty());
159
160    bool is_secure = pfi.isSecure();
161    Addr am_addr = pfi.getAddr() / hotZoneSize;
162    Addr current_block = (pfi.getAddr() % hotZoneSize) / blkSize;
163    uint64_t lines_per_zone = hotZoneSize / blkSize;
164
165    // Get the entries of the curent block (am_addr), the previous, and the
166    // following ones
167    AccessMapEntry *am_entry_curr = getAccessMapEntry(am_addr, is_secure);
168    AccessMapEntry *am_entry_prev = (am_addr > 0) ?
169        getAccessMapEntry(am_addr-1, is_secure) : nullptr;
170    AccessMapEntry *am_entry_next = (am_addr < (MaxAddr/hotZoneSize)) ?
171        getAccessMapEntry(am_addr+1, is_secure) : nullptr;
172    assert(am_entry_curr != am_entry_prev);
173    assert(am_entry_curr != am_entry_next);
174    assert(am_entry_prev != am_entry_next);
175    assert(am_entry_curr != nullptr);
176
177    //Mark the current access as Accessed
178    setEntryState(*am_entry_curr, current_block, AM_ACCESS);
179
180    /**
181     * Create a contiguous copy of the 3 entries states.
182     * With this, we avoid doing boundaries checking in the loop that looks
183     * for prefetch candidates, mark out of range positions with AM_INVALID
184     */
185    std::vector<AccessMapState> states(3 * lines_per_zone);
186    for (unsigned idx = 0; idx < lines_per_zone; idx += 1) {
187        states[idx] =
188            am_entry_prev != nullptr ? am_entry_prev->states[idx] : AM_INVALID;
189        states[idx + lines_per_zone] = am_entry_curr->states[idx];
190        states[idx + 2 * lines_per_zone] =
191            am_entry_next != nullptr ? am_entry_next->states[idx] : AM_INVALID;
192    }
193
194    /**
195     * am_entry_prev->states => states[               0 ..   lines_per_zone-1]
196     * am_entry_curr->states => states[  lines_per_zone .. 2*lines_per_zone-1]
197     * am_entry_next->states => states[2*lines_per_zone .. 3*lines_per_zone-1]
198     */
199
200    // index of the current_block in the new vector
201    Addr states_current_block = current_block + lines_per_zone;
202    // consider strides 1..lines_per_zone/2
203    int max_stride = limitStride == 0 ? lines_per_zone / 2 : limitStride + 1;
204    for (int stride = 1; stride < max_stride; stride += 1) {
205        // Test accessed positive strides
206        if (checkCandidate(states, states_current_block, stride)) {
207            // candidate found, current_block - stride
208            Addr pf_addr;
209            if (stride > current_block) {
210                // The index (current_block - stride) falls in the range of
211                // the previous zone (am_entry_prev), adjust the address
212                // accordingly
213                Addr blk = states_current_block - stride;
214                pf_addr = (am_addr - 1) * hotZoneSize + blk * blkSize;
215                setEntryState(*am_entry_prev, blk, AM_PREFETCH);
216            } else {
217                // The index (current_block - stride) falls within
218                // am_entry_curr
219                Addr blk = current_block - stride;
220                pf_addr = am_addr * hotZoneSize + blk * blkSize;
221                setEntryState(*am_entry_curr, blk, AM_PREFETCH);
222            }
223            addresses.push_back(QueuedPrefetcher::AddrPriority(pf_addr, 0));
224            if (addresses.size() == degree) {
225                break;
226            }
227        }
228
229        // Test accessed negative strides
230        if (checkCandidate(states, states_current_block, -stride)) {
231            // candidate found, current_block + stride
232            Addr pf_addr;
233            if (current_block + stride >= lines_per_zone) {
234                // The index (current_block + stride) falls in the range of
235                // the next zone (am_entry_next), adjust the address
236                // accordingly
237                Addr blk = (states_current_block + stride) % lines_per_zone;
238                pf_addr = (am_addr + 1) * hotZoneSize + blk * blkSize;
239                setEntryState(*am_entry_next, blk, AM_PREFETCH);
240            } else {
241                // The index (current_block + stride) falls within
242                // am_entry_curr
243                Addr blk = current_block + stride;
244                pf_addr = am_addr * hotZoneSize + blk * blkSize;
245                setEntryState(*am_entry_curr, blk, AM_PREFETCH);
246            }
247            addresses.push_back(QueuedPrefetcher::AddrPriority(pf_addr, 0));
248            if (addresses.size() == degree) {
249                break;
250            }
251        }
252    }
253}
254
255AccessMapPatternMatching*
256AccessMapPatternMatchingParams::create()
257{
258    return new AccessMapPatternMatching(this);
259}
260
261AMPMPrefetcher::AMPMPrefetcher(const AMPMPrefetcherParams *p)
262  : QueuedPrefetcher(p), ampm(*p->ampm)
263{
264}
265
266void
267AMPMPrefetcher::calculatePrefetch(const PrefetchInfo &pfi,
268    std::vector<AddrPriority> &addresses)
269{
270    ampm.calculatePrefetch(pfi, addresses);
271}
272
273AMPMPrefetcher*
274AMPMPrefetcherParams::create()
275{
276    return new AMPMPrefetcher(this);
277}
278