snoop_filter.hh revision 11129:48c02e8b0bbb 
1/*
2 * Copyright (c) 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 * 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#ifndef __MEM_SNOOP_FILTER_HH__
46#define __MEM_SNOOP_FILTER_HH__
47
48#include <utility>
49
50#include "base/hashmap.hh"
51#include "mem/packet.hh"
52#include "mem/port.hh"
53#include "mem/qport.hh"
54#include "params/SnoopFilter.hh"
55#include "sim/sim_object.hh"
56#include "sim/system.hh"
57
58/**
59 * This snoop filter keeps track of which connected port has a
60 * particular line of data. It can be queried (through lookup*) on
61 * memory requests from above (reads / writes / ...); and also from
62 * below (snoops). The snoop filter precisely knows about the location
63 * of lines "above" it through a map from cache line address to
64 * sharers/ports. The snoop filter ties into the flows of requests
65 * (when they succeed at the lower interface), regular responses from
66 * below and also responses from sideway's caches (in update*). This
67 * allows the snoop filter to model cache-line residency by snooping
68 * the messages.
69 *
70 * The tracking happens in two fields to be able to distinguish
71 * between in-flight requests (in requested) and already pulled in
72 * lines (in holder). This distinction is used for producing tighter
73 * assertions and tracking request completion. For safety, (requested
74 * | holder) should be notified and the requesting MSHRs will take
75 * care of ordering.
76 *
77 * Overall, some trickery is required because:
78 * (1) snoops are not followed by an ACK, but only evoke a response if
79 *     they need to (hit dirty)
80 * (2) side-channel information is funnelled through direct modifications of
81 *     pkt, instead of proper messages through the bus
82 * (3) there are no clean evict messages telling the snoop filter that a local,
83 *     upper cache dropped a line, making the snoop filter pessimistic for now
84 * (4) ordering: there is no single point of order in the system.  Instead,
85 *     requesting MSHRs track order between local requests and remote snoops
86 */
87class SnoopFilter : public SimObject {
88  public:
89    typedef std::vector<QueuedSlavePort*> SnoopList;
90
91    SnoopFilter (const SnoopFilterParams *p) : SimObject(p),
92        linesize(p->system->cacheLineSize()), lookupLatency(p->lookup_latency)
93    {
94    }
95
96    /**
97     * Init a new snoop filter and tell it about all the slave ports of the
98     * enclosing bus.
99     *
100     * @param bus_slave_ports Vector of slave ports that the bus is attached to.
101     */
102    void setSlavePorts(const SnoopList& bus_slave_ports) {
103        slavePorts = bus_slave_ports;
104    }
105
106    /**
107     * Lookup a request (from a slave port) in the snoop filter and return a
108     * list of other slave ports that need forwarding of the resulting snoops.
109     * Additionally, update the tracking structures with new request
110     * information.
111     *
112     * @param cpkt          Pointer to the request packet.  Not changed.
113     * @param slave_port    Slave port where the request came from.
114     * @return Pair of a vector of snoop target ports and lookup latency.
115     */
116    std::pair<SnoopList, Cycles> lookupRequest(const Packet* cpkt,
117                                               const SlavePort& slave_port);
118
119    /**
120     * For a successful request, update all data structures in the snoop filter
121     * reflecting the changes caused by that request
122     *
123     * @param cpkt          Pointer to the request packet.  Not changed.
124     * @param slave_port    Slave port where the request came from.
125     * @param will_retry    This request will retry on this bus / snoop filter
126     */
127    void updateRequest(const Packet* cpkt, const SlavePort& slave_port,
128                       bool will_retry);
129
130    /**
131     * Handle an incoming snoop from below (the master port).  These can upgrade the
132     * tracking logic and may also benefit from additional steering thanks to the
133     * snoop filter.
134     * @param cpkt Pointer to const Packet containing the snoop.
135     * @return Pair with a vector of SlavePorts that need snooping and a lookup
136     *         latency.
137     */
138    std::pair<SnoopList, Cycles> lookupSnoop(const Packet* cpkt);
139
140    /**
141     * Let the snoop filter see any snoop responses that turn into request responses
142     * and indicate cache to cache transfers.  These will update the corresponding
143     * state in the filter.
144     *
145     * @param cpkt     Pointer to const Packet holding the snoop response.
146     * @param rsp_port SlavePort that sends the response.
147     * @param req_port SlavePort that made the original request and is the
148     *                 destination of the snoop response.
149     */
150    void updateSnoopResponse(const Packet *cpkt, const SlavePort& rsp_port,
151                             const SlavePort& req_port);
152
153    /**
154     * Pass snoop responses that travel downward through the snoop filter and let
155     * them update the snoop filter state.  No additional routing happens.
156     *
157     * @param cpkt     Pointer to const Packet holding the snoop response.
158     * @param rsp_port SlavePort that sends the response.
159     * @param req_port MasterPort through which the response leaves this cluster.
160     */
161    void updateSnoopForward(const Packet *cpkt, const SlavePort& rsp_port,
162                            const MasterPort& req_port);
163
164    /**
165     * Update the snoop filter with a response from below (outer / other cache,
166     * or memory) and update the tracking information in the snoop filter.
167     *
168     * @param cpkt       Pointer to const Packet holding the snoop response.
169     * @param slave_port SlavePort that made the original request and is the target
170     *                   of this response.
171     */
172    void updateResponse(const Packet *cpkt, const SlavePort& slave_port);
173
174    /**
175     * Simple factory methods for standard return values for lookupRequest
176     */
177    std::pair<SnoopList, Cycles> snoopAll(Cycles latency) const
178    {
179        return std::make_pair(slavePorts, latency);
180    }
181    std::pair<SnoopList, Cycles> snoopSelected(const SnoopList& slave_ports,
182                                               Cycles latency) const
183    {
184        return std::make_pair(slave_ports, latency);
185    }
186    std::pair<SnoopList, Cycles> snoopDown(Cycles latency) const
187    {
188        SnoopList empty;
189        return std::make_pair(empty , latency);
190    }
191
192    virtual void regStats();
193
194  protected:
195    typedef uint64_t SnoopMask;
196   /**
197    * Per cache line item tracking a bitmask of SlavePorts who have an
198    * outstanding request to this line (requested) or already share a cache line
199    * with this address (holder).
200    */
201    struct SnoopItem {
202        SnoopMask requested;
203        SnoopMask holder;
204    };
205    /**
206     * HashMap of SnoopItems indexed by line address
207     */
208    typedef m5::hash_map<Addr, SnoopItem> SnoopFilterCache;
209
210    /**
211     * Convert a single port to a corresponding, one-hot bitmask
212     * @param port SlavePort that should be converted.
213     * @return One-hot bitmask corresponding to the port.
214     */
215    SnoopMask portToMask(const SlavePort& port) const;
216    /**
217     * Convert multiple ports to a corresponding bitmask
218     * @param ports SnoopList that should be converted.
219     * @return Bitmask corresponding to the ports in the list.
220     */
221    SnoopMask portListToMask(const SnoopList& ports) const;
222    /**
223     * Converts a bitmask of ports into the corresponing list of ports
224     * @param ports SnoopMask of the requested ports
225     * @return SnoopList containing all the requested SlavePorts
226     */
227    SnoopList maskToPortList(SnoopMask ports) const;
228
229  private:
230
231    /**
232     * Removes snoop filter items which have no requesters and no holders.
233     */
234    void eraseIfNullEntry(SnoopFilterCache::iterator& sf_it);
235    /** Simple hash set of cached addresses. */
236    SnoopFilterCache cachedLocations;
237    /**
238     * Variable to temporarily store value of snoopfilter entry
239     * incase updateRequest needs to undo changes made in lookupRequest
240     * (because of crossbar retry)
241     */
242    SnoopItem retryItem;
243    /** List of all attached slave ports. */
244    SnoopList slavePorts;
245    /** Cache line size. */
246    const unsigned linesize;
247    /** Latency for doing a lookup in the filter */
248    const Cycles lookupLatency;
249
250    /** Statistics */
251    Stats::Scalar totRequests;
252    Stats::Scalar hitSingleRequests;
253    Stats::Scalar hitMultiRequests;
254
255    Stats::Scalar totSnoops;
256    Stats::Scalar hitSingleSnoops;
257    Stats::Scalar hitMultiSnoops;
258};
259
260inline SnoopFilter::SnoopMask
261SnoopFilter::portToMask(const SlavePort& port) const
262{
263    unsigned id = (unsigned)port.getId();
264    assert(id != (unsigned)InvalidPortID);
265    assert((int)id < 8 * sizeof(SnoopMask));
266
267    return ((SnoopMask)1) << id;
268}
269
270inline SnoopFilter::SnoopMask
271SnoopFilter::portListToMask(const SnoopList& ports) const
272{
273    SnoopMask m = 0;
274    for (auto port = ports.begin(); port != ports.end(); ++port)
275        m |= portToMask(**port);
276    return m;
277}
278
279inline SnoopFilter::SnoopList
280SnoopFilter::maskToPortList(SnoopMask port_mask) const
281{
282    SnoopList res;
283    for (auto port = slavePorts.begin(); port != slavePorts.end(); ++port)
284        if (port_mask & portToMask(**port))
285            res.push_back(*port);
286    return res;
287}
288#endif // __MEM_SNOOP_FILTER_HH__
289