1/*
2 * Copyright (c) 2005 The Regents of The University of Michigan
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;

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29 * Steve Reinhardt
30 */
31
32/**
33 * @file
34 * Stride Prefetcher template instantiations.
35 */
36
37#include "base/trace.hh"
38#include "mem/cache/prefetch/stride.hh"
39
40void
41StridePrefetcher::calculatePrefetch(PacketPtr &pkt, std::list<Addr> &addresses,
42 std::list<Tick> &delays)
43{
44 if (!pkt->req->hasPC()) {
45 DPRINTF(HWPrefetch, "ignoring request with no PC");
46 return;
47 }
48
49 Addr blk_addr = pkt->getAddr() & ~(Addr)(blkSize-1);
50 int ctx_id = useContextId ? pkt->req->contextId() : 0;
51 Addr pc = pkt->req->getPC();
52 assert(ctx_id < Max_Contexts);
53 std::list<StrideEntry*> &tab = table[ctx_id];
54
55 /* Scan Table for instAddr Match */
56 std::list<StrideEntry*>::iterator iter;
57 for (iter = tab.begin(); iter != tab.end(); iter++) {
58 if ((*iter)->instAddr == pc)
59 break;
60 }
61
62 if (iter != tab.end()) {
63 // Hit in table
64
65 int new_stride = blk_addr - (*iter)->missAddr;
66 bool stride_match = (new_stride == (*iter)->stride);
67
68 if (stride_match && new_stride != 0) {
69 if ((*iter)->confidence < Max_Conf)
70 (*iter)->confidence++;
71 } else {
72 (*iter)->stride = new_stride;
73 if ((*iter)->confidence > Min_Conf)
74 (*iter)->confidence = 0;
75 }
76
77 DPRINTF(HWPrefetch, "hit: PC %x blk_addr %x stride %d (%s), conf %d\n",
78 pc, blk_addr, new_stride, stride_match ? "match" : "change",
79 (*iter)->confidence);
80
81 (*iter)->missAddr = blk_addr;
82
83 if ((*iter)->confidence <= 0)
84 return;
85
86 for (int d = 1; d <= degree; d++) {
87 Addr new_addr = blk_addr + d * new_stride;
88 if (pageStop && !samePage(blk_addr, new_addr)) {
89 // Spanned the page, so now stop
90 pfSpanPage += degree - d + 1;
91 return;
92 } else {
93 DPRINTF(HWPrefetch, " queuing prefetch to %x @ %d\n",
94 new_addr, latency);
95 addresses.push_back(new_addr);
96 delays.push_back(latency);
97 }
98 }
99 } else {
100 // Miss in table
101 // Find lowest confidence and replace
102
103 DPRINTF(HWPrefetch, "miss: PC %x blk_addr %x\n", pc, blk_addr);
104
105 if (tab.size() >= 256) { //set default table size is 256
106 std::list<StrideEntry*>::iterator min_pos = tab.begin();
107 int min_conf = (*min_pos)->confidence;
108 for (iter = min_pos, ++iter; iter != tab.end(); ++iter) {
109 if ((*iter)->confidence < min_conf){
110 min_pos = iter;
111 min_conf = (*iter)->confidence;
112 }
113 }
114 DPRINTF(HWPrefetch, " replacing PC %x\n", (*min_pos)->instAddr);
115 tab.erase(min_pos);
116 }
117
118 StrideEntry *new_entry = new StrideEntry;
119 new_entry->instAddr = pc;
120 new_entry->missAddr = blk_addr;
121 new_entry->stride = 0;
122 new_entry->confidence = 0;
123 tab.push_back(new_entry);
124 }
125}