stride.cc revision 13426:d2b0e9ec67f1 
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 <cassert>
52
53#include "base/intmath.hh"
54#include "base/logging.hh"
55#include "base/random.hh"
56#include "base/trace.hh"
57#include "debug/HWPrefetch.hh"
58#include "params/StridePrefetcher.hh"
59
60StridePrefetcher::StrideEntry::StrideEntry()
61{
62    invalidate();
63}
64
65void
66StridePrefetcher::StrideEntry::invalidate()
67{
68    instAddr = 0;
69    lastAddr = 0;
70    isSecure = false;
71    stride = 0;
72    confidence = 0;
73}
74
75StridePrefetcher::StridePrefetcher(const StridePrefetcherParams *p)
76    : QueuedPrefetcher(p),
77      maxConf(p->max_conf),
78      threshConf(p->thresh_conf),
79      minConf(p->min_conf),
80      startConf(p->start_conf),
81      pcTableAssoc(p->table_assoc),
82      pcTableSets(p->table_sets),
83      useMasterId(p->use_master_id),
84      degree(p->degree)
85{
86    assert(isPowerOf2(pcTableSets));
87}
88
89StridePrefetcher::PCTable*
90StridePrefetcher::findTable(int context)
91{
92    // Check if table for given context exists
93    auto it = pcTables.find(context);
94    if (it != pcTables.end())
95        return &it->second;
96
97    // If table does not exist yet, create one
98    return allocateNewContext(context);
99}
100
101StridePrefetcher::PCTable*
102StridePrefetcher::allocateNewContext(int context)
103{
104    // Create new table
105    auto insertion_result = pcTables.insert(std::make_pair(context,
106        PCTable(pcTableAssoc, pcTableSets, name())));
107
108    DPRINTF(HWPrefetch, "Adding context %i with stride entries\n", context);
109
110    // Get iterator to new pc table, and then return a pointer to the new table
111    return &(insertion_result.first->second);
112}
113
114StridePrefetcher::PCTable::PCTable(int assoc, int sets, const std::string name)
115    : pcTableAssoc(assoc), pcTableSets(sets), _name(name), entries(pcTableSets)
116{
117    for (auto& set : entries) {
118        set.resize(pcTableAssoc);
119    }
120}
121
122StridePrefetcher::PCTable::~PCTable()
123{
124}
125
126void
127StridePrefetcher::calculatePrefetch(const PacketPtr &pkt,
128                                    std::vector<AddrPriority> &addresses)
129{
130    if (!pkt->req->hasPC()) {
131        DPRINTF(HWPrefetch, "Ignoring request with no PC.\n");
132        return;
133    }
134
135    // Get required packet info
136    Addr pkt_addr = pkt->getAddr();
137    Addr pc = pkt->req->getPC();
138    bool is_secure = pkt->isSecure();
139    MasterID master_id = useMasterId ? pkt->req->masterId() : 0;
140
141    // Get corresponding pc table
142    PCTable* pcTable = findTable(master_id);
143
144    // Search for entry in the pc table
145    StrideEntry *entry = pcTable->findEntry(pc, is_secure);
146
147    if (entry != nullptr) {
148        // Hit in table
149        int new_stride = pkt_addr - entry->lastAddr;
150        bool stride_match = (new_stride == entry->stride);
151
152        // Adjust confidence for stride entry
153        if (stride_match && new_stride != 0) {
154            if (entry->confidence < maxConf)
155                entry->confidence++;
156        } else {
157            if (entry->confidence > minConf)
158                entry->confidence--;
159            // If confidence has dropped below the threshold, train new stride
160            if (entry->confidence < threshConf)
161                entry->stride = new_stride;
162        }
163
164        DPRINTF(HWPrefetch, "Hit: PC %x pkt_addr %x (%s) stride %d (%s), "
165                "conf %d\n", pc, pkt_addr, is_secure ? "s" : "ns", new_stride,
166                stride_match ? "match" : "change",
167                entry->confidence);
168
169        entry->lastAddr = pkt_addr;
170
171        // Abort prefetch generation if below confidence threshold
172        if (entry->confidence < threshConf)
173            return;
174
175        // Generate up to degree prefetches
176        for (int d = 1; d <= degree; d++) {
177            // Round strides up to atleast 1 cacheline
178            int prefetch_stride = new_stride;
179            if (abs(new_stride) < blkSize) {
180                prefetch_stride = (new_stride < 0) ? -blkSize : blkSize;
181            }
182
183            Addr new_addr = pkt_addr + d * prefetch_stride;
184            if (samePage(pkt_addr, new_addr)) {
185                DPRINTF(HWPrefetch, "Queuing prefetch to %#x.\n", new_addr);
186                addresses.push_back(AddrPriority(new_addr, 0));
187            } else {
188                // Record the number of page crossing prefetches generated
189                pfSpanPage += degree - d + 1;
190                DPRINTF(HWPrefetch, "Ignoring page crossing prefetch.\n");
191                return;
192            }
193        }
194    } else {
195        // Miss in table
196        DPRINTF(HWPrefetch, "Miss: PC %x pkt_addr %x (%s)\n", pc, pkt_addr,
197                is_secure ? "s" : "ns");
198
199        StrideEntry* entry = pcTable->findVictim(pc);
200
201        // Invalidate victim
202        entry->invalidate();
203
204        // Insert new entry's data
205        entry->instAddr = pc;
206        entry->lastAddr = pkt_addr;
207        entry->isSecure= is_secure;
208        entry->confidence = startConf;
209    }
210}
211
212inline Addr
213StridePrefetcher::PCTable::pcHash(Addr pc) const
214{
215    Addr hash1 = pc >> 1;
216    Addr hash2 = hash1 >> floorLog2(pcTableSets);
217    return (hash1 ^ hash2) & (Addr)(pcTableSets - 1);
218}
219
220inline StridePrefetcher::StrideEntry*
221StridePrefetcher::PCTable::findVictim(Addr pc)
222{
223    // Rand replacement for now
224    int set = pcHash(pc);
225    int way = random_mt.random<int>(0, pcTableAssoc - 1);
226
227    DPRINTF(HWPrefetch, "Victimizing lookup table[%d][%d].\n", set, way);
228    return &entries[set][way];
229}
230
231inline StridePrefetcher::StrideEntry*
232StridePrefetcher::PCTable::findEntry(Addr pc, bool is_secure)
233{
234    int set = pcHash(pc);
235    std::vector<StrideEntry>& set_entries = entries[set];
236    for (int way = 0; way < pcTableAssoc; way++) {
237        StrideEntry* entry = &set_entries[way];
238        // Search ways for match
239        if ((entry->instAddr == pc) && (entry->isSecure == is_secure)) {
240            DPRINTF(HWPrefetch, "Lookup hit table[%d][%d].\n", set, way);
241            return entry;
242        }
243    }
244    return nullptr;
245}
246
247StridePrefetcher*
248StridePrefetcherParams::create()
249{
250    return new StridePrefetcher(this);
251}
252