1/*
2 * Copyright (c) 2012-2013 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

--- 32 unchanged lines hidden (view full) ---

41 * Steve Reinhardt
42 */
43
44/**
45 * @file
46 * Stride Prefetcher template instantiations.
47 */
48
49#include "debug/HWPrefetch.hh"
50#include "mem/cache/prefetch/stride.hh"
51
52StridePrefetcher::StridePrefetcher(const StridePrefetcherParams *p)
53 : QueuedPrefetcher(p),
54 maxConf(p->max_conf),
55 threshConf(p->thresh_conf),
56 minConf(p->min_conf),
57 startConf(p->start_conf),
58 pcTableAssoc(p->table_assoc),
59 pcTableSets(p->table_sets),
60 useMasterId(p->use_master_id),
61 degree(p->degree)
62{
63 // Don't consult stride prefetcher on instruction accesses
64 onInst = false;
65
66 assert(isPowerOf2(pcTableSets));
67
68 for (int c = 0; c < maxContexts; c++) {
69 pcTable[c] = new StrideEntry*[pcTableSets];
70 for (int s = 0; s < pcTableSets; s++) {
71 pcTable[c][s] = new StrideEntry[pcTableAssoc];
72 }
73 }
74}
75
76StridePrefetcher::~StridePrefetcher()
77{
78 for (int c = 0; c < maxContexts; c++) {
79 for (int s = 0; s < pcTableSets; s++) {
80 delete[] pcTable[c][s];
81 }
82 }
83}
84
85void
86StridePrefetcher::calculatePrefetch(const PacketPtr &pkt,
87 std::vector<Addr> &addresses)
88{
89 if (!pkt->req->hasPC()) {
90 DPRINTF(HWPrefetch, "Ignoring request with no PC.\n");
91 return;
92 }
93
94 // Get required packet info
95 Addr pkt_addr = pkt->getAddr();
96 Addr pc = pkt->req->getPC();
97 bool is_secure = pkt->isSecure();
98 MasterID master_id = useMasterId ? pkt->req->masterId() : 0;
99
100 assert(master_id < maxContexts);
101
102 // Lookup pc-based information
103 StrideEntry *entry;
104
105 if(pcTableHit(pc, is_secure, master_id, entry)) {
106 // Hit in table
107 int new_stride = pkt_addr - entry->lastAddr;
108 bool stride_match = (new_stride == entry->stride);
109
110 // Adjust confidence for stride entry
111 if (stride_match && new_stride != 0) {
112 if (entry->confidence < maxConf)
113 entry->confidence++;
114 } else {
115 if (entry->confidence > minConf)
116 entry->confidence--;
117 // If confidence has dropped below the threshold, train new stride
118 if (entry->confidence < threshConf)
119 entry->stride = new_stride;
120 }
121
122 DPRINTF(HWPrefetch, "Hit: PC %x pkt_addr %x (%s) stride %d (%s), "
123 "conf %d\n", pc, pkt_addr, is_secure ? "s" : "ns", new_stride,
124 stride_match ? "match" : "change",
125 entry->confidence);
126
127 entry->lastAddr = pkt_addr;
128
129 // Abort prefetch generation if below confidence threshold
130 if (entry->confidence < threshConf)
131 return;
132
133 // Generate up to degree prefetches
134 for (int d = 1; d <= degree; d++) {
135 // Round strides up to atleast 1 cacheline
136 int prefetch_stride = new_stride;
137 if (abs(new_stride) < blkSize) {
138 prefetch_stride = (new_stride < 0) ? -blkSize : blkSize;
139 }
140
141 Addr new_addr = pkt_addr + d * prefetch_stride;
142 if (samePage(pkt_addr, new_addr)) {
143 DPRINTF(HWPrefetch, "Queuing prefetch to %#x.\n", new_addr);
144 addresses.push_back(new_addr);
145 } else {
146 // Record the number of page crossing prefetches generated
147 pfSpanPage += degree - d + 1;
148 DPRINTF(HWPrefetch, "Ignoring page crossing prefetch.\n");
149 return;
150 }
151 }
152 } else {
153 // Miss in table
154 DPRINTF(HWPrefetch, "Miss: PC %x pkt_addr %x (%s)\n", pc, pkt_addr,
155 is_secure ? "s" : "ns");
156
157 StrideEntry* entry = pcTableVictim(pc, master_id);
158 entry->instAddr = pc;
159 entry->lastAddr = pkt_addr;
160 entry->isSecure= is_secure;
161 entry->stride = 0;
162 entry->confidence = startConf;
163 }
164}
165
166inline Addr
167StridePrefetcher::pcHash(Addr pc) const
168{
169 Addr hash1 = pc >> 1;
170 Addr hash2 = hash1 >> floorLog2(pcTableSets);
171 return (hash1 ^ hash2) & (Addr)(pcTableSets - 1);
172}
173
174inline StridePrefetcher::StrideEntry*
175StridePrefetcher::pcTableVictim(Addr pc, int master_id)
176{
177 // Rand replacement for now
178 int set = pcHash(pc);
179 int way = rand() % pcTableAssoc;
180
181 DPRINTF(HWPrefetch, "Victimizing lookup table[%d][%d].\n", set, way);
182 return &pcTable[master_id][set][way];
183}
184
185inline bool
186StridePrefetcher::pcTableHit(Addr pc, bool is_secure, int master_id,
187 StrideEntry* &entry)
188{
189 int set = pcHash(pc);
190 StrideEntry* set_entries = pcTable[master_id][set];
191 for (int way = 0; way < pcTableAssoc; way++) {
192 // Search ways for match
193 if (set_entries[way].instAddr == pc &&
194 set_entries[way].isSecure == is_secure) {
195 DPRINTF(HWPrefetch, "Lookup hit table[%d][%d].\n", set, way);
196 entry = &set_entries[way];
197 return true;
198 }
199 }
200 return false;
201}
202
203StridePrefetcher*
204StridePrefetcherParams::create()
205{
206 return new StridePrefetcher(this);
207}