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 "base/trace.hh"
50#include "debug/HWPrefetch.hh"
51#include "mem/cache/prefetch/stride.hh"
52
53void
54StridePrefetcher::calculatePrefetch(PacketPtr &pkt, std::list<Addr> &addresses,
55 std::list<Cycles> &delays)
56{
57 if (!pkt->req->hasPC()) {
58 DPRINTF(HWPrefetch, "ignoring request with no PC");
59 return;
60 }
61
62 Addr data_addr = pkt->getAddr();
63 bool is_secure = pkt->isSecure();
64 MasterID master_id = useMasterId ? pkt->req->masterId() : 0;
65 Addr pc = pkt->req->getPC();
66 assert(master_id < Max_Contexts);
67 std::list<StrideEntry*> &tab = table[master_id];
68
69 // Revert to simple N-block ahead prefetch for instruction fetches
70 if (instTagged && pkt->req->isInstFetch()) {
71 for (int d = 1; d <= degree; d++) {
72 Addr new_addr = data_addr + d * blkSize;
73 if (pageStop && !samePage(data_addr, new_addr)) {
74 // Spanned the page, so now stop
75 pfSpanPage += degree - d + 1;
76 return;
77 }
78 DPRINTF(HWPrefetch, "queuing prefetch to %x @ %d\n",
79 new_addr, latency);
80 addresses.push_back(new_addr);
81 delays.push_back(latency);
82 }
83 return;
84 }
85
86 /* Scan Table for instAddr Match */
87 std::list<StrideEntry*>::iterator iter;
88 for (iter = tab.begin(); iter != tab.end(); iter++) {
89 // Entries have to match on the security state as well
90 if ((*iter)->instAddr == pc && (*iter)->isSecure == is_secure)
91 break;
92 }
93
94 if (iter != tab.end()) {
95 // Hit in table
96
97 int new_stride = data_addr - (*iter)->missAddr;
98 bool stride_match = (new_stride == (*iter)->stride);
99
100 if (stride_match && new_stride != 0) {
101 (*iter)->tolerance = true;
102 if ((*iter)->confidence < Max_Conf)
103 (*iter)->confidence++;
104 } else {
105 if (!((*iter)->tolerance)) {
106 (*iter)->stride = new_stride;
107 if ((*iter)->confidence > Min_Conf)
108 (*iter)->confidence = 0;
109 } else {
110 (*iter)->tolerance = false;
111 }
112 }
113
114 DPRINTF(HWPrefetch, "hit: PC %x data_addr %x (%s) stride %d (%s), "
115 "conf %d\n", pc, data_addr, is_secure ? "s" : "ns", new_stride,
116 stride_match ? "match" : "change",
117 (*iter)->confidence);
118
119 (*iter)->missAddr = data_addr;
120 (*iter)->isSecure = is_secure;
121
122 if ((*iter)->confidence <= 0)
123 return;
124
125 for (int d = 1; d <= degree; d++) {
126 Addr new_addr = data_addr + d * (*iter)->stride;
127 if (pageStop && !samePage(data_addr, new_addr)) {
128 // Spanned the page, so now stop
129 pfSpanPage += degree - d + 1;
130 return;
131 } else {
132 DPRINTF(HWPrefetch, " queuing prefetch to %x (%s) @ %d\n",
133 new_addr, is_secure ? "s" : "ns", latency);
134 addresses.push_back(new_addr);
135 delays.push_back(latency);
136 }
137 }
138 } else {
139 // Miss in table
140 // Find lowest confidence and replace
141
142 DPRINTF(HWPrefetch, "miss: PC %x data_addr %x (%s)\n", pc, data_addr,
143 is_secure ? "s" : "ns");
144
145 if (tab.size() >= 256) { //set default table size is 256
146 std::list<StrideEntry*>::iterator min_pos = tab.begin();
147 int min_conf = (*min_pos)->confidence;
148 for (iter = min_pos, ++iter; iter != tab.end(); ++iter) {
149 if ((*iter)->confidence < min_conf){
150 min_pos = iter;
151 min_conf = (*iter)->confidence;
152 }
153 }
154 DPRINTF(HWPrefetch, " replacing PC %x (%s)\n",
155 (*min_pos)->instAddr, (*min_pos)->isSecure ? "s" : "ns");
156
157 // free entry and delete it
158 delete *min_pos;
159 tab.erase(min_pos);
160 }
161
162 StrideEntry *new_entry = new StrideEntry;
163 new_entry->instAddr = pc;
164 new_entry->missAddr = data_addr;
165 new_entry->isSecure = is_secure;
166 new_entry->stride = 0;
167 new_entry->confidence = 0;
168 new_entry->tolerance = false;
169 tab.push_back(new_entry);
170 }
171}
172
173
174StridePrefetcher*
175StridePrefetcherParams::create()
176{
177 return new StridePrefetcher(this);
178}