queued.cc revision 13624:3d8220c2d41d 
1/*
2 * Copyright (c) 2014-2015 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 * Redistribution and use in source and binary forms, with or without
15 * modification, are permitted provided that the following conditions are
16 * met: redistributions of source code must retain the above copyright
17 * notice, this list of conditions and the following disclaimer;
18 * redistributions in binary form must reproduce the above copyright
19 * notice, this list of conditions and the following disclaimer in the
20 * documentation and/or other materials provided with the distribution;
21 * neither the name of the copyright holders nor the names of its
22 * contributors may be used to endorse or promote products derived from
23 * this software without specific prior written permission.
24 *
25 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
26 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
27 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
28 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
29 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
30 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
31 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
32 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
33 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
34 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
35 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
36 *
37 * Authors: Mitch Hayenga
38 */
39
40#include "mem/cache/prefetch/queued.hh"
41
42#include <cassert>
43
44#include "base/logging.hh"
45#include "base/trace.hh"
46#include "debug/HWPrefetch.hh"
47#include "mem/request.hh"
48#include "params/QueuedPrefetcher.hh"
49
50QueuedPrefetcher::QueuedPrefetcher(const QueuedPrefetcherParams *p)
51    : BasePrefetcher(p), queueSize(p->queue_size), latency(p->latency),
52      queueSquash(p->queue_squash), queueFilter(p->queue_filter),
53      cacheSnoop(p->cache_snoop), tagPrefetch(p->tag_prefetch)
54{
55
56}
57
58QueuedPrefetcher::~QueuedPrefetcher()
59{
60    // Delete the queued prefetch packets
61    for (DeferredPacket &p : pfq) {
62        delete p.pkt;
63    }
64}
65
66void
67QueuedPrefetcher::notify(const PacketPtr &pkt, const PrefetchInfo &pfi)
68{
69    Addr blk_addr = blockAddress(pfi.getAddr());
70    bool is_secure = pfi.isSecure();
71
72    // Squash queued prefetches if demand miss to same line
73    if (queueSquash) {
74        auto itr = pfq.begin();
75        while (itr != pfq.end()) {
76            if (itr->pfInfo.getAddr() == blk_addr &&
77                itr->pfInfo.isSecure() == is_secure) {
78                delete itr->pkt;
79                itr = pfq.erase(itr);
80            } else {
81                ++itr;
82            }
83        }
84    }
85
86    // Calculate prefetches given this access
87    std::vector<AddrPriority> addresses;
88    calculatePrefetch(pfi, addresses);
89
90    // Queue up generated prefetches
91    for (AddrPriority& addr_prio : addresses) {
92
93        // Block align prefetch address
94        addr_prio.first = blockAddress(addr_prio.first);
95
96        if (samePage(pfi.getAddr(), addr_prio.first)) {
97            PrefetchInfo new_pfi(pfi,addr_prio.first);
98
99            pfIdentified++;
100            DPRINTF(HWPrefetch, "Found a pf candidate addr: %#x, "
101                    "inserting into prefetch queue.\n", new_pfi.getAddr());
102
103            // Create and insert the request
104            insert(pkt, new_pfi, addr_prio.second);
105        } else {
106            // Record the number of page crossing prefetches generate
107            pfSpanPage += 1;
108            DPRINTF(HWPrefetch, "Ignoring page crossing prefetch.\n");
109        }
110    }
111}
112
113PacketPtr
114QueuedPrefetcher::getPacket()
115{
116    DPRINTF(HWPrefetch, "Requesting a prefetch to issue.\n");
117
118    if (pfq.empty()) {
119        DPRINTF(HWPrefetch, "No hardware prefetches available.\n");
120        return nullptr;
121    }
122
123    PacketPtr pkt = pfq.front().pkt;
124    pfq.pop_front();
125
126    pfIssued++;
127    issuedPrefetches += 1;
128    assert(pkt != nullptr);
129    DPRINTF(HWPrefetch, "Generating prefetch for %#x.\n", pkt->getAddr());
130    return pkt;
131}
132
133QueuedPrefetcher::const_iterator
134QueuedPrefetcher::inPrefetch(const PrefetchInfo &pfi) const
135{
136    for (const_iterator dp = pfq.begin(); dp != pfq.end(); dp++) {
137        if (dp->pfInfo.sameAddr(pfi)) return dp;
138    }
139
140    return pfq.end();
141}
142
143QueuedPrefetcher::iterator
144QueuedPrefetcher::inPrefetch(const PrefetchInfo &pfi)
145{
146    for (iterator dp = pfq.begin(); dp != pfq.end(); dp++) {
147        if (dp->pfInfo.sameAddr(pfi)) return dp;
148    }
149
150    return pfq.end();
151}
152
153void
154QueuedPrefetcher::regStats()
155{
156    BasePrefetcher::regStats();
157
158    pfIdentified
159        .name(name() + ".pfIdentified")
160        .desc("number of prefetch candidates identified");
161
162    pfBufferHit
163        .name(name() + ".pfBufferHit")
164        .desc("number of redundant prefetches already in prefetch queue");
165
166    pfInCache
167        .name(name() + ".pfInCache")
168        .desc("number of redundant prefetches already in cache/mshr dropped");
169
170    pfRemovedFull
171        .name(name() + ".pfRemovedFull")
172        .desc("number of prefetches dropped due to prefetch queue size");
173
174    pfSpanPage
175        .name(name() + ".pfSpanPage")
176        .desc("number of prefetches not generated due to page crossing");
177}
178
179void
180QueuedPrefetcher::insert(const PacketPtr &pkt, PrefetchInfo &new_pfi,
181                         int32_t priority)
182{
183    if (queueFilter) {
184        iterator it = inPrefetch(new_pfi);
185        /* If the address is already in the queue, update priority and leave */
186        if (it != pfq.end()) {
187            pfBufferHit++;
188            if (it->priority < priority) {
189                /* Update priority value and position in the queue */
190                it->priority = priority;
191                iterator prev = it;
192                bool cont = true;
193                while (cont && prev != pfq.begin()) {
194                    prev--;
195                    /* If the packet has higher priority, swap */
196                    if (*it > *prev) {
197                        std::swap(*it, *prev);
198                        it = prev;
199                    }
200                }
201                DPRINTF(HWPrefetch, "Prefetch addr already in "
202                    "prefetch queue, priority updated\n");
203            } else {
204                DPRINTF(HWPrefetch, "Prefetch addr already in "
205                    "prefetch queue\n");
206            }
207            return;
208        }
209    }
210
211    Addr target_addr = new_pfi.getAddr();
212    if (useVirtualAddresses) {
213        assert(pkt->req->hasPaddr());
214        //if we trained with virtual addresses, compute the phsysical address
215        if (new_pfi.getAddr() >= pkt->req->getVaddr()) {
216            //positive stride
217            target_addr = pkt->req->getPaddr() +
218                (new_pfi.getAddr() - pkt->req->getVaddr());
219        } else {
220            //negative stride
221            target_addr = pkt->req->getPaddr() -
222                (pkt->req->getVaddr() - new_pfi.getAddr());
223        }
224    }
225
226    if (cacheSnoop && (inCache(target_addr, new_pfi.isSecure()) ||
227                inMissQueue(target_addr, new_pfi.isSecure()))) {
228        pfInCache++;
229        DPRINTF(HWPrefetch, "Dropping redundant in "
230                "cache/MSHR prefetch addr:%#x\n", target_addr);
231        return;
232    }
233
234    /* Create a prefetch memory request */
235    RequestPtr pf_req =
236        std::make_shared<Request>(target_addr, blkSize, 0, masterId);
237
238    if (new_pfi.isSecure()) {
239        pf_req->setFlags(Request::SECURE);
240    }
241    pf_req->taskId(ContextSwitchTaskId::Prefetcher);
242    PacketPtr pf_pkt = new Packet(pf_req, MemCmd::HardPFReq);
243    pf_pkt->allocate();
244    if (tagPrefetch && new_pfi.hasPC()) {
245        // Tag prefetch packet with  accessing pc
246        pf_pkt->req->setPC(new_pfi.getPC());
247    }
248
249    /* Verify prefetch buffer space for request */
250    if (pfq.size() == queueSize) {
251        pfRemovedFull++;
252        /* Lowest priority packet */
253        iterator it = pfq.end();
254        panic_if (it == pfq.begin(), "Prefetch queue is both full and empty!");
255        --it;
256        /* Look for oldest in that level of priority */
257        panic_if (it == pfq.begin(), "Prefetch queue is full with 1 element!");
258        iterator prev = it;
259        bool cont = true;
260        /* While not at the head of the queue */
261        while (cont && prev != pfq.begin()) {
262            prev--;
263            /* While at the same level of priority */
264            cont = prev->priority == it->priority;
265            if (cont)
266                /* update pointer */
267                it = prev;
268        }
269        DPRINTF(HWPrefetch, "Prefetch queue full, removing lowest priority "
270                            "oldest packet, addr: %#x", it->pfInfo.getAddr());
271        delete it->pkt;
272        pfq.erase(it);
273    }
274
275    Tick pf_time = curTick() + clockPeriod() * latency;
276    DPRINTF(HWPrefetch, "Prefetch queued. "
277            "addr:%#x priority: %3d tick:%lld.\n",
278            target_addr, priority, pf_time);
279
280    /* Create the packet and find the spot to insert it */
281    DeferredPacket dpp(new_pfi, pf_time, pf_pkt, priority);
282    if (pfq.size() == 0) {
283        pfq.emplace_back(dpp);
284    } else {
285        iterator it = pfq.end();
286        do {
287            --it;
288        } while (it != pfq.begin() && dpp > *it);
289        /* If we reach the head, we have to see if the new element is new head
290         * or not */
291        if (it == pfq.begin() && dpp <= *it)
292            it++;
293        pfq.insert(it, dpp);
294    }
295}
296