stride.cc revision 8831:6c08a877af8f 
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;
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: Ron Dreslinski
29 *          Steve Reinhardt
30 */
31
32/**
33 * @file
34 * Stride Prefetcher template instantiations.
35 */
36
37#include "base/trace.hh"
38#include "debug/HWPrefetch.hh"
39#include "mem/cache/prefetch/stride.hh"
40
41void
42StridePrefetcher::calculatePrefetch(PacketPtr &pkt, std::list<Addr> &addresses,
43                                    std::list<Tick> &delays)
44{
45    if (!pkt->req->hasPC()) {
46        DPRINTF(HWPrefetch, "ignoring request with no PC");
47        return;
48    }
49
50    if (useContextId && !pkt->req->hasContextId()) {
51        DPRINTF(HWPrefetch, "ignoring request with no context ID");
52        return;
53    }
54
55    Addr blk_addr = pkt->getAddr() & ~(Addr)(blkSize-1);
56    int ctx_id = useContextId ? pkt->req->contextId() : 0;
57    Addr pc = pkt->req->getPC();
58    assert(ctx_id < Max_Contexts);
59    std::list<StrideEntry*> &tab = table[ctx_id];
60
61    /* Scan Table for instAddr Match */
62    std::list<StrideEntry*>::iterator iter;
63    for (iter = tab.begin(); iter != tab.end(); iter++) {
64        if ((*iter)->instAddr == pc)
65            break;
66    }
67
68    if (iter != tab.end()) {
69        // Hit in table
70
71        int new_stride = blk_addr - (*iter)->missAddr;
72        bool stride_match = (new_stride == (*iter)->stride);
73
74        if (stride_match && new_stride != 0) {
75            if ((*iter)->confidence < Max_Conf)
76                (*iter)->confidence++;
77        } else {
78            (*iter)->stride = new_stride;
79            if ((*iter)->confidence > Min_Conf)
80                (*iter)->confidence = 0;
81        }
82
83        DPRINTF(HWPrefetch, "hit: PC %x blk_addr %x stride %d (%s), conf %d\n",
84                pc, blk_addr, new_stride, stride_match ? "match" : "change",
85                (*iter)->confidence);
86
87        (*iter)->missAddr = blk_addr;
88
89        if ((*iter)->confidence <= 0)
90            return;
91
92        for (int d = 1; d <= degree; d++) {
93            Addr new_addr = blk_addr + d * new_stride;
94            if (pageStop && !samePage(blk_addr, new_addr)) {
95                // Spanned the page, so now stop
96                pfSpanPage += degree - d + 1;
97                return;
98            } else {
99                DPRINTF(HWPrefetch, "  queuing prefetch to %x @ %d\n",
100                        new_addr, latency);
101                addresses.push_back(new_addr);
102                delays.push_back(latency);
103            }
104        }
105    } else {
106        // Miss in table
107        // Find lowest confidence and replace
108
109        DPRINTF(HWPrefetch, "miss: PC %x blk_addr %x\n", pc, blk_addr);
110
111        if (tab.size() >= 256) { //set default table size is 256
112            std::list<StrideEntry*>::iterator min_pos = tab.begin();
113            int min_conf = (*min_pos)->confidence;
114            for (iter = min_pos, ++iter; iter != tab.end(); ++iter) {
115                if ((*iter)->confidence < min_conf){
116                    min_pos = iter;
117                    min_conf = (*iter)->confidence;
118                }
119            }
120            DPRINTF(HWPrefetch, "  replacing PC %x\n", (*min_pos)->instAddr);
121
122            // free entry and delete it
123            delete *min_pos;
124            tab.erase(min_pos);
125        }
126
127        StrideEntry *new_entry = new StrideEntry;
128        new_entry->instAddr = pc;
129        new_entry->missAddr = blk_addr;
130        new_entry->stride = 0;
131        new_entry->confidence = 0;
132        tab.push_back(new_entry);
133    }
134}
135
136
137StridePrefetcher*
138StridePrefetcherParams::create()
139{
140   return new StridePrefetcher(this);
141}
142