snoop_filter.cc revision 10403 
1/*
2 * Copyright (c) 2013 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: Stephan Diestelhorst <stephan.diestelhorst@arm.com>
38 */
39
40/**
41 * @file
42 * Definition of a snoop filter.
43 */
44
45#include "base/misc.hh"
46#include "base/trace.hh"
47#include "debug/SnoopFilter.hh"
48#include "mem/snoop_filter.hh"
49#include "sim/system.hh"
50
51std::pair<SnoopFilter::SnoopList, Cycles>
52SnoopFilter::lookupRequest(const Packet* cpkt, const SlavePort& slave_port)
53{
54    DPRINTF(SnoopFilter, "%s: packet src %s addr 0x%x cmd %s\n",
55            __func__, slave_port.name(), cpkt->getAddr(), cpkt->cmdString());
56
57    Addr line_addr = cpkt->getAddr() & ~(linesize - 1);
58    SnoopMask req_port = portToMask(slave_port);
59    auto sf_it = cachedLocations.find(line_addr);
60    bool is_hit = (sf_it != cachedLocations.end());
61    // Create a new element through operator[] and modify in-place
62    SnoopItem& sf_item = is_hit ? sf_it->second : cachedLocations[line_addr];
63    SnoopMask interested = sf_item.holder | sf_item.requested;
64
65    totRequests++;
66    if (is_hit) {
67        // Single bit set -> value is a power of two
68        if (isPow2(interested))
69            hitSingleRequests++;
70        else
71            hitMultiRequests++;
72    }
73
74    DPRINTF(SnoopFilter, "%s:   SF value %x.%x\n",
75            __func__, sf_item.requested, sf_item.holder);
76
77    if (cpkt->needsResponse()) {
78        if (!cpkt->memInhibitAsserted()) {
79            // Max one request per address per port
80            panic_if(sf_item.requested & req_port, "double request :( "\
81                     "SF value %x.%x\n", sf_item.requested, sf_item.holder);
82
83            // Mark in-flight requests to distinguish later on
84            sf_item.requested |= req_port;
85        } else {
86            // NOTE: The memInhibit might have been asserted by a cache closer
87            // to the CPU, already -> the response will not be seen by this
88            // filter -> we do not need to keep the in-flight request, but make
89            // sure that we know that that cluster has a copy
90            panic_if(!(sf_item.holder & req_port), "Need to hold the value!");
91            DPRINTF(SnoopFilter, "%s:   not marking request. SF value %x.%x\n",
92                    __func__,  sf_item.requested, sf_item.holder);
93        }
94        DPRINTF(SnoopFilter, "%s:   new SF value %x.%x\n",
95                __func__,  sf_item.requested, sf_item.holder);
96    }
97    return snoopSelected(maskToPortList(interested & ~req_port), lookupLatency);
98}
99
100void
101SnoopFilter::updateRequest(const Packet* cpkt, const SlavePort& slave_port,
102                           bool will_retry)
103{
104    DPRINTF(SnoopFilter, "%s: packet src %s addr 0x%x cmd %s\n",
105            __func__, slave_port.name(), cpkt->getAddr(), cpkt->cmdString());
106
107    Addr line_addr = cpkt->getAddr() & ~(linesize - 1);
108    SnoopMask req_port = portToMask(slave_port);
109    SnoopItem& sf_item  = cachedLocations[line_addr];
110
111    DPRINTF(SnoopFilter, "%s:   old SF value %x.%x retry: %i\n",
112            __func__, sf_item.requested, sf_item.holder, will_retry);
113
114    if (will_retry) {
115        // Unmark a request that will come again.
116        sf_item.requested &= ~req_port;
117        return;
118    }
119
120    // will_retry == false
121    if (!cpkt->needsResponse()) {
122        // Packets that will not evoke a response but still need updates of the
123        // snoop filter; WRITEBACKs for now only
124        if (cpkt->cmd == MemCmd::Writeback) {
125            // make sure that the sender actually had the line
126            panic_if(sf_item.requested & req_port, "double request :( "\
127                     "SF value %x.%x\n", sf_item.requested, sf_item.holder);
128            panic_if(!(sf_item.holder & req_port), "requester %x is not a "\
129                     "holder :( SF value %x.%x\n", req_port,
130                     sf_item.requested, sf_item.holder);
131            // Writebacks -> the sender does not have the line anymore
132            sf_item.holder &= ~req_port;
133        } else {
134            assert(0 == "Handle non-writeback, here");
135        }
136        DPRINTF(SnoopFilter, "%s:   new SF value %x.%x\n",
137                __func__,  sf_item.requested, sf_item.holder);
138    }
139}
140
141std::pair<SnoopFilter::SnoopList, Cycles>
142SnoopFilter::lookupSnoop(const Packet* cpkt)
143{
144    DPRINTF(SnoopFilter, "%s: packet addr 0x%x cmd %s\n",
145            __func__, cpkt->getAddr(), cpkt->cmdString());
146
147    assert(cpkt->isRequest());
148
149    // Broadcast / filter upward snoops
150    const bool filter_upward = true;  // @todo: Make configurable
151
152    if (!filter_upward)
153        return snoopAll(lookupLatency);
154
155    Addr line_addr = cpkt->getAddr() & ~(linesize - 1);
156    auto sf_it = cachedLocations.find(line_addr);
157    bool is_hit = (sf_it != cachedLocations.end());
158    // Create a new element through operator[] and modify in-place
159    SnoopItem& sf_item = is_hit ? sf_it->second : cachedLocations[line_addr];
160
161    DPRINTF(SnoopFilter, "%s:   old SF value %x.%x\n",
162            __func__, sf_item.requested, sf_item.holder);
163
164    SnoopMask interested = (sf_item.holder | sf_item.requested);
165
166    totSnoops++;
167    if (is_hit) {
168        // Single bit set -> value is a power of two
169        if (isPow2(interested))
170            hitSingleSnoops++;
171        else
172            hitMultiSnoops++;
173    }
174
175    assert(cpkt->isInvalidate() == cpkt->needsExclusive());
176    if (cpkt->isInvalidate() && !sf_item.requested) {
177        // Early clear of the holder, if no other request is currently going on
178        // @todo: This should possibly be updated even though we do not filter
179        // upward snoops
180        sf_item.holder = 0;
181    }
182
183    DPRINTF(SnoopFilter, "%s:   new SF value %x.%x interest: %x \n",
184            __func__, sf_item.requested, sf_item.holder, interested);
185
186    return snoopSelected(maskToPortList(interested), lookupLatency);
187}
188
189void
190SnoopFilter::updateSnoopResponse(const Packet* cpkt,
191                                 const SlavePort& rsp_port,
192                                 const SlavePort& req_port)
193{
194    DPRINTF(SnoopFilter, "%s: packet rsp %s req %s addr 0x%x cmd %s\n",
195            __func__, rsp_port.name(), req_port.name(), cpkt->getAddr(),
196            cpkt->cmdString());
197
198    Addr line_addr = cpkt->getAddr() & ~(linesize - 1);
199    SnoopMask rsp_mask = portToMask(rsp_port);
200    SnoopMask req_mask = portToMask(req_port);
201    SnoopItem& sf_item = cachedLocations[line_addr];
202
203    assert(cpkt->isResponse());
204    assert(cpkt->memInhibitAsserted());
205
206    DPRINTF(SnoopFilter, "%s:   old SF value %x.%x\n",
207            __func__,  sf_item.requested, sf_item.holder);
208
209    // The source should have the line
210    panic_if(!(sf_item.holder & rsp_mask), "SF value %x.%x does not have "\
211             "the line\n", sf_item.requested, sf_item.holder);
212
213    // The destination should have had a request in
214    panic_if(!(sf_item.requested & req_mask), "SF value %x.%x missing "\
215             "the original request\n",  sf_item.requested, sf_item.holder);
216
217    // Update the residency of the cache line.
218    if (cpkt->needsExclusive() || !cpkt->sharedAsserted()) {
219        DPRINTF(SnoopFilter, "%s:  dropping %x because needs: %i shared: %i "\
220                "SF val: %x.%x\n", __func__,  rsp_mask,
221                cpkt->needsExclusive(), cpkt->sharedAsserted(),
222                sf_item.requested, sf_item.holder);
223
224        sf_item.holder &= ~rsp_mask;
225        // The snoop filter does not see any ACKs from non-responding sharers
226        // that have been invalidated :(  So below assert would be nice, but..
227        //assert(sf_item.holder == 0);
228        sf_item.holder = 0;
229    }
230    assert(cpkt->cmd != MemCmd::Writeback);
231    sf_item.holder |=  req_mask;
232    sf_item.requested &= ~req_mask;
233    DPRINTF(SnoopFilter, "%s:   new SF value %x.%x\n",
234            __func__, sf_item.requested, sf_item.holder);
235}
236
237void
238SnoopFilter::updateSnoopForward(const Packet* cpkt,
239        const SlavePort& rsp_port, const MasterPort& req_port)
240{
241    DPRINTF(SnoopFilter, "%s: packet rsp %s req %s addr 0x%x cmd %s\n",
242            __func__, rsp_port.name(), req_port.name(), cpkt->getAddr(),
243            cpkt->cmdString());
244
245    Addr line_addr = cpkt->getAddr() & ~(linesize - 1);
246    SnoopItem& sf_item = cachedLocations[line_addr];
247    SnoopMask rsp_mask M5_VAR_USED = portToMask(rsp_port);
248
249    assert(cpkt->isResponse());
250    assert(cpkt->memInhibitAsserted());
251
252    DPRINTF(SnoopFilter, "%s:   old SF value %x.%x\n",
253            __func__,  sf_item.requested, sf_item.holder);
254
255    // Remote (to this snoop filter) snoops update the filter already when they
256    // arrive from below, because we may not see any response.
257    if (cpkt->needsExclusive()) {
258        // If the request to this snoop response hit an in-flight transaction,
259        // the holder was not reset -> no assertion & do that here, now!
260        //assert(sf_item.holder == 0);
261        sf_item.holder = 0;
262    }
263    DPRINTF(SnoopFilter, "%s:   new SF value %x.%x\n",
264            __func__, sf_item.requested, sf_item.holder);
265}
266
267void
268SnoopFilter::updateResponse(const Packet* cpkt, const SlavePort& slave_port)
269{
270    DPRINTF(SnoopFilter, "%s: packet src %s addr 0x%x cmd %s\n",
271            __func__, slave_port.name(), cpkt->getAddr(), cpkt->cmdString());
272
273    Addr line_addr = cpkt->getAddr() & ~(linesize - 1);
274    SnoopMask slave_mask = portToMask(slave_port);
275    SnoopItem& sf_item = cachedLocations[line_addr];
276
277    assert(cpkt->isResponse());
278
279    DPRINTF(SnoopFilter, "%s:   old SF value %x.%x\n",
280            __func__,  sf_item.requested, sf_item.holder);
281
282    // Make sure we have seen the actual request, too
283    panic_if(!(sf_item.requested & slave_mask), "SF value %x.%x missing "\
284             "request bit\n", sf_item.requested, sf_item.holder);
285
286    // Update the residency of the cache line.
287    if (cpkt->needsExclusive() || !cpkt->sharedAsserted())
288        sf_item.holder = 0;
289    sf_item.holder |=  slave_mask;
290    sf_item.requested &= ~slave_mask;
291    DPRINTF(SnoopFilter, "%s:   new SF value %x.%x\n",
292            __func__, sf_item.requested, sf_item.holder);
293}
294
295void
296SnoopFilter::regStats()
297{
298    totRequests
299        .name(name() + ".tot_requests")
300        .desc("Total number of requests made to the snoop filter.");
301
302    hitSingleRequests
303        .name(name() + ".hit_single_requests")
304        .desc("Number of requests hitting in the snoop filter with a single "\
305              "holder of the requested data.");
306
307    hitMultiRequests
308        .name(name() + ".hit_multi_requests")
309        .desc("Number of requests hitting in the snoop filter with multiple "\
310              "(>1) holders of the requested data.");
311
312    totSnoops
313        .name(name() + ".tot_snoops")
314        .desc("Total number of snoops made to the snoop filter.");
315
316    hitSingleSnoops
317        .name(name() + ".hit_single_snoops")
318        .desc("Number of snoops hitting in the snoop filter with a single "\
319              "holder of the requested data.");
320
321    hitMultiSnoops
322        .name(name() + ".hit_multi_snoops")
323        .desc("Number of snoops hitting in the snoop filter with multiple "\
324              "(>1) holders of the requested data.");
325}
326
327SnoopFilter *
328SnoopFilterParams::create()
329{
330    return new SnoopFilter(this);
331}
332