stride.cc revision 13425:00abf35b2f7e 
1/*
2 * Copyright (c) 2012-2013, 2015 ARM Limited
3 * All rights reserved
4 *
5 * The license below extends only to copyright in the software and shall
6 * not be construed as granting a license to any other intellectual
7 * property including but not limited to intellectual property relating
8 * to a hardware implementation of the functionality of the software
9 * licensed hereunder.  You may use the software subject to the license
10 * terms below provided that you ensure that this notice is replicated
11 * unmodified and in its entirety in all distributions of the software,
12 * modified or unmodified, in source code or in binary form.
13 *
14 * Copyright (c) 2005 The Regents of The University of Michigan
15 * All rights reserved.
16 *
17 * Redistribution and use in source and binary forms, with or without
18 * modification, are permitted provided that the following conditions are
19 * met: redistributions of source code must retain the above copyright
20 * notice, this list of conditions and the following disclaimer;
21 * redistributions in binary form must reproduce the above copyright
22 * notice, this list of conditions and the following disclaimer in the
23 * documentation and/or other materials provided with the distribution;
24 * neither the name of the copyright holders nor the names of its
25 * contributors may be used to endorse or promote products derived from
26 * this software without specific prior written permission.
27 *
28 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
29 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
30 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
31 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
32 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
33 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
34 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
35 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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38 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
39 *
40 * Authors: Ron Dreslinski
41 *          Steve Reinhardt
42 */
43
44/**
45 * @file
46 * Stride Prefetcher template instantiations.
47 */
48
49#include "mem/cache/prefetch/stride.hh"
50
51#include <cassert>
52
53#include "base/intmath.hh"
54#include "base/logging.hh"
55#include "base/random.hh"
56#include "base/trace.hh"
57#include "debug/HWPrefetch.hh"
58#include "params/StridePrefetcher.hh"
59
60StridePrefetcher::StridePrefetcher(const StridePrefetcherParams *p)
61    : QueuedPrefetcher(p),
62      maxConf(p->max_conf),
63      threshConf(p->thresh_conf),
64      minConf(p->min_conf),
65      startConf(p->start_conf),
66      pcTableAssoc(p->table_assoc),
67      pcTableSets(p->table_sets),
68      useMasterId(p->use_master_id),
69      degree(p->degree)
70{
71    assert(isPowerOf2(pcTableSets));
72}
73
74StridePrefetcher::PCTable*
75StridePrefetcher::findTable(int context)
76{
77    // Check if table for given context exists
78    auto it = pcTables.find(context);
79    if (it != pcTables.end())
80        return &it->second;
81
82    // If table does not exist yet, create one
83    return allocateNewContext(context);
84}
85
86StridePrefetcher::PCTable*
87StridePrefetcher::allocateNewContext(int context)
88{
89    // Create new table
90    auto insertion_result = pcTables.insert(std::make_pair(context,
91        PCTable(pcTableAssoc, pcTableSets, name())));
92
93    DPRINTF(HWPrefetch, "Adding context %i with stride entries\n", context);
94
95    // Get iterator to new pc table, and then return a pointer to the new table
96    return &(insertion_result.first->second);
97}
98
99StridePrefetcher::PCTable::PCTable(int assoc, int sets, const std::string name)
100    : pcTableAssoc(assoc), pcTableSets(sets), _name(name), entries(pcTableSets)
101{
102    for (auto& set : entries) {
103        set.resize(pcTableAssoc);
104    }
105}
106
107StridePrefetcher::PCTable::~PCTable()
108{
109}
110
111void
112StridePrefetcher::calculatePrefetch(const PacketPtr &pkt,
113                                    std::vector<AddrPriority> &addresses)
114{
115    if (!pkt->req->hasPC()) {
116        DPRINTF(HWPrefetch, "Ignoring request with no PC.\n");
117        return;
118    }
119
120    // Get required packet info
121    Addr pkt_addr = pkt->getAddr();
122    Addr pc = pkt->req->getPC();
123    bool is_secure = pkt->isSecure();
124    MasterID master_id = useMasterId ? pkt->req->masterId() : 0;
125
126    // Get corresponding pc table
127    PCTable* pcTable = findTable(master_id);
128
129    // Search for entry in the pc table
130    StrideEntry *entry = pcTable->findEntry(pc, is_secure);
131
132    if (entry != nullptr) {
133        // Hit in table
134        int new_stride = pkt_addr - entry->lastAddr;
135        bool stride_match = (new_stride == entry->stride);
136
137        // Adjust confidence for stride entry
138        if (stride_match && new_stride != 0) {
139            if (entry->confidence < maxConf)
140                entry->confidence++;
141        } else {
142            if (entry->confidence > minConf)
143                entry->confidence--;
144            // If confidence has dropped below the threshold, train new stride
145            if (entry->confidence < threshConf)
146                entry->stride = new_stride;
147        }
148
149        DPRINTF(HWPrefetch, "Hit: PC %x pkt_addr %x (%s) stride %d (%s), "
150                "conf %d\n", pc, pkt_addr, is_secure ? "s" : "ns", new_stride,
151                stride_match ? "match" : "change",
152                entry->confidence);
153
154        entry->lastAddr = pkt_addr;
155
156        // Abort prefetch generation if below confidence threshold
157        if (entry->confidence < threshConf)
158            return;
159
160        // Generate up to degree prefetches
161        for (int d = 1; d <= degree; d++) {
162            // Round strides up to atleast 1 cacheline
163            int prefetch_stride = new_stride;
164            if (abs(new_stride) < blkSize) {
165                prefetch_stride = (new_stride < 0) ? -blkSize : blkSize;
166            }
167
168            Addr new_addr = pkt_addr + d * prefetch_stride;
169            if (samePage(pkt_addr, new_addr)) {
170                DPRINTF(HWPrefetch, "Queuing prefetch to %#x.\n", new_addr);
171                addresses.push_back(AddrPriority(new_addr, 0));
172            } else {
173                // Record the number of page crossing prefetches generated
174                pfSpanPage += degree - d + 1;
175                DPRINTF(HWPrefetch, "Ignoring page crossing prefetch.\n");
176                return;
177            }
178        }
179    } else {
180        // Miss in table
181        DPRINTF(HWPrefetch, "Miss: PC %x pkt_addr %x (%s)\n", pc, pkt_addr,
182                is_secure ? "s" : "ns");
183
184        StrideEntry* entry = pcTable->findVictim(pc);
185        entry->instAddr = pc;
186        entry->lastAddr = pkt_addr;
187        entry->isSecure= is_secure;
188        entry->stride = 0;
189        entry->confidence = startConf;
190    }
191}
192
193inline Addr
194StridePrefetcher::PCTable::pcHash(Addr pc) const
195{
196    Addr hash1 = pc >> 1;
197    Addr hash2 = hash1 >> floorLog2(pcTableSets);
198    return (hash1 ^ hash2) & (Addr)(pcTableSets - 1);
199}
200
201inline StridePrefetcher::StrideEntry*
202StridePrefetcher::PCTable::findVictim(Addr pc)
203{
204    // Rand replacement for now
205    int set = pcHash(pc);
206    int way = random_mt.random<int>(0, pcTableAssoc - 1);
207
208    DPRINTF(HWPrefetch, "Victimizing lookup table[%d][%d].\n", set, way);
209    return &entries[set][way];
210}
211
212inline StridePrefetcher::StrideEntry*
213StridePrefetcher::PCTable::findEntry(Addr pc, bool is_secure)
214{
215    int set = pcHash(pc);
216    std::vector<StrideEntry>& set_entries = entries[set];
217    for (int way = 0; way < pcTableAssoc; way++) {
218        StrideEntry* entry = &set_entries[way];
219        // Search ways for match
220        if ((entry->instAddr == pc) && (entry->isSecure == is_secure)) {
221            DPRINTF(HWPrefetch, "Lookup hit table[%d][%d].\n", set, way);
222            return entry;
223        }
224    }
225    return nullptr;
226}
227
228StridePrefetcher*
229StridePrefetcherParams::create()
230{
231    return new StridePrefetcher(this);
232}
233