stride.cc revision 11800:54436a1784dc 
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 "base/random.hh"
52#include "base/trace.hh"
53#include "debug/HWPrefetch.hh"
54
55StridePrefetcher::StridePrefetcher(const StridePrefetcherParams *p)
56    : QueuedPrefetcher(p),
57      maxConf(p->max_conf),
58      threshConf(p->thresh_conf),
59      minConf(p->min_conf),
60      startConf(p->start_conf),
61      pcTableAssoc(p->table_assoc),
62      pcTableSets(p->table_sets),
63      useMasterId(p->use_master_id),
64      degree(p->degree),
65      pcTable(pcTableAssoc, pcTableSets, name())
66{
67    // Don't consult stride prefetcher on instruction accesses
68    onInst = false;
69
70    assert(isPowerOf2(pcTableSets));
71}
72
73StridePrefetcher::StrideEntry**
74StridePrefetcher::PCTable::allocateNewContext(int context)
75{
76    auto res = entries.insert(std::make_pair(context,
77                              new StrideEntry*[pcTableSets]));
78    auto it = res.first;
79    chatty_assert(res.second, "Allocating an already created context\n");
80    assert(it->first == context);
81
82    DPRINTF(HWPrefetch, "Adding context %i with stride entries at %p\n",
83            context, it->second);
84
85    StrideEntry** entry = it->second;
86    for (int s = 0; s < pcTableSets; s++) {
87        entry[s] = new StrideEntry[pcTableAssoc];
88    }
89    return entry;
90}
91
92StridePrefetcher::PCTable::~PCTable() {
93    for (auto entry : entries) {
94        for (int s = 0; s < pcTableSets; s++) {
95            delete[] entry.second[s];
96        }
97        delete[] entry.second;
98    }
99}
100
101void
102StridePrefetcher::calculatePrefetch(const PacketPtr &pkt,
103                                    std::vector<AddrPriority> &addresses)
104{
105    if (!pkt->req->hasPC()) {
106        DPRINTF(HWPrefetch, "Ignoring request with no PC.\n");
107        return;
108    }
109
110    // Get required packet info
111    Addr pkt_addr = pkt->getAddr();
112    Addr pc = pkt->req->getPC();
113    bool is_secure = pkt->isSecure();
114    MasterID master_id = useMasterId ? pkt->req->masterId() : 0;
115
116    // Lookup pc-based information
117    StrideEntry *entry;
118
119    if (pcTableHit(pc, is_secure, master_id, entry)) {
120        // Hit in table
121        int new_stride = pkt_addr - entry->lastAddr;
122        bool stride_match = (new_stride == entry->stride);
123
124        // Adjust confidence for stride entry
125        if (stride_match && new_stride != 0) {
126            if (entry->confidence < maxConf)
127                entry->confidence++;
128        } else {
129            if (entry->confidence > minConf)
130                entry->confidence--;
131            // If confidence has dropped below the threshold, train new stride
132            if (entry->confidence < threshConf)
133                entry->stride = new_stride;
134        }
135
136        DPRINTF(HWPrefetch, "Hit: PC %x pkt_addr %x (%s) stride %d (%s), "
137                "conf %d\n", pc, pkt_addr, is_secure ? "s" : "ns", new_stride,
138                stride_match ? "match" : "change",
139                entry->confidence);
140
141        entry->lastAddr = pkt_addr;
142
143        // Abort prefetch generation if below confidence threshold
144        if (entry->confidence < threshConf)
145            return;
146
147        // Generate up to degree prefetches
148        for (int d = 1; d <= degree; d++) {
149            // Round strides up to atleast 1 cacheline
150            int prefetch_stride = new_stride;
151            if (abs(new_stride) < blkSize) {
152                prefetch_stride = (new_stride < 0) ? -blkSize : blkSize;
153            }
154
155            Addr new_addr = pkt_addr + d * prefetch_stride;
156            if (samePage(pkt_addr, new_addr)) {
157                DPRINTF(HWPrefetch, "Queuing prefetch to %#x.\n", new_addr);
158                addresses.push_back(AddrPriority(new_addr, 0));
159            } else {
160                // Record the number of page crossing prefetches generated
161                pfSpanPage += degree - d + 1;
162                DPRINTF(HWPrefetch, "Ignoring page crossing prefetch.\n");
163                return;
164            }
165        }
166    } else {
167        // Miss in table
168        DPRINTF(HWPrefetch, "Miss: PC %x pkt_addr %x (%s)\n", pc, pkt_addr,
169                is_secure ? "s" : "ns");
170
171        StrideEntry* entry = pcTableVictim(pc, master_id);
172        entry->instAddr = pc;
173        entry->lastAddr = pkt_addr;
174        entry->isSecure= is_secure;
175        entry->stride = 0;
176        entry->confidence = startConf;
177    }
178}
179
180inline Addr
181StridePrefetcher::pcHash(Addr pc) const
182{
183    Addr hash1 = pc >> 1;
184    Addr hash2 = hash1 >> floorLog2(pcTableSets);
185    return (hash1 ^ hash2) & (Addr)(pcTableSets - 1);
186}
187
188inline StridePrefetcher::StrideEntry*
189StridePrefetcher::pcTableVictim(Addr pc, int master_id)
190{
191    // Rand replacement for now
192    int set = pcHash(pc);
193    int way = random_mt.random<int>(0, pcTableAssoc - 1);
194
195    DPRINTF(HWPrefetch, "Victimizing lookup table[%d][%d].\n", set, way);
196    return &pcTable[master_id][set][way];
197}
198
199inline bool
200StridePrefetcher::pcTableHit(Addr pc, bool is_secure, int master_id,
201                             StrideEntry* &entry)
202{
203    int set = pcHash(pc);
204    StrideEntry* set_entries = pcTable[master_id][set];
205    for (int way = 0; way < pcTableAssoc; way++) {
206        // Search ways for match
207        if (set_entries[way].instAddr == pc &&
208            set_entries[way].isSecure == is_secure) {
209            DPRINTF(HWPrefetch, "Lookup hit table[%d][%d].\n", set, way);
210            entry = &set_entries[way];
211            return true;
212        }
213    }
214    return false;
215}
216
217StridePrefetcher*
218StridePrefetcherParams::create()
219{
220    return new StridePrefetcher(this);
221}
222