base_set_assoc.hh revision 12684:44ebd2bc020f 
1/*
2 * Copyright (c) 2012-2014,2017 ARM Limited
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4 *
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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) 2003-2005,2014 The Regents of The University of Michigan
15 * All rights reserved.
16 *
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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;
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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
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33 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
34 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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38 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
39 *
40 * Authors: Erik Hallnor
41 */
42
43/**
44 * @file
45 * Declaration of a base set associative tag store.
46 */
47
48#ifndef __MEM_CACHE_TAGS_BASE_SET_ASSOC_HH__
49#define __MEM_CACHE_TAGS_BASE_SET_ASSOC_HH__
50
51#include <cassert>
52#include <cstring>
53#include <vector>
54
55#include "debug/CacheRepl.hh"
56#include "mem/cache/base.hh"
57#include "mem/cache/blk.hh"
58#include "mem/cache/replacement_policies/base.hh"
59#include "mem/cache/tags/base.hh"
60#include "mem/cache/tags/cacheset.hh"
61#include "mem/packet.hh"
62#include "params/BaseSetAssoc.hh"
63
64/**
65 * A BaseSetAssoc cache tag store.
66 * @sa  \ref gem5MemorySystem "gem5 Memory System"
67 *
68 * The BaseSetAssoc placement policy divides the cache into s sets of w
69 * cache lines (ways). A cache line is mapped onto a set, and can be placed
70 * into any of the ways of this set.
71 */
72class BaseSetAssoc : public BaseTags
73{
74  public:
75    /** Typedef the block type used in this tag store. */
76    typedef CacheBlk BlkType;
77    /** Typedef the set type used in this tag store. */
78    typedef CacheSet<CacheBlk> SetType;
79
80  protected:
81    /** The associativity of the cache. */
82    const unsigned assoc;
83    /** The allocatable associativity of the cache (alloc mask). */
84    unsigned allocAssoc;
85
86    /** The cache blocks. */
87    std::vector<BlkType> blks;
88
89    /** The number of sets in the cache. */
90    const unsigned numSets;
91
92    /** Whether tags and data are accessed sequentially. */
93    const bool sequentialAccess;
94
95    /** The cache sets. */
96    std::vector<SetType> sets;
97
98    /** The amount to shift the address to get the set. */
99    int setShift;
100    /** The amount to shift the address to get the tag. */
101    int tagShift;
102    /** Mask out all bits that aren't part of the set index. */
103    unsigned setMask;
104
105    /** Replacement policy */
106    BaseReplacementPolicy *replacementPolicy;
107
108  public:
109    /** Convenience typedef. */
110     typedef BaseSetAssocParams Params;
111
112    /**
113     * Construct and initialize this tag store.
114     */
115    BaseSetAssoc(const Params *p);
116
117    /**
118     * Destructor
119     */
120    virtual ~BaseSetAssoc() {};
121
122    /**
123     * This function updates the tags when a block is invalidated but does
124     * not invalidate the block itself. It also updates the replacement data.
125     *
126     * @param blk The block to invalidate.
127     */
128    void invalidate(CacheBlk *blk) override;
129
130    /**
131     * Find the cache block given set and way
132     * @param set The set of the block.
133     * @param way The way of the block.
134     * @return The cache block.
135     */
136    CacheBlk *findBlockBySetAndWay(int set, int way) const override;
137
138    /**
139     * Access block and update replacement data. May not succeed, in which case
140     * nullptr is returned. This has all the implications of a cache
141     * access and should only be used as such. Returns the access latency as a
142     * side effect.
143     * @param addr The address to find.
144     * @param is_secure True if the target memory space is secure.
145     * @param lat The access latency.
146     * @return Pointer to the cache block if found.
147     */
148    CacheBlk* accessBlock(Addr addr, bool is_secure, Cycles &lat) override
149    {
150        BlkType *blk = findBlock(addr, is_secure);
151
152        // Access all tags in parallel, hence one in each way.  The data side
153        // either accesses all blocks in parallel, or one block sequentially on
154        // a hit.  Sequential access with a miss doesn't access data.
155        tagAccesses += allocAssoc;
156        if (sequentialAccess) {
157            if (blk != nullptr) {
158                dataAccesses += 1;
159            }
160        } else {
161            dataAccesses += allocAssoc;
162        }
163
164        if (blk != nullptr) {
165            // If a cache hit
166            lat = accessLatency;
167            // Check if the block to be accessed is available. If not,
168            // apply the accessLatency on top of block->whenReady.
169            if (blk->whenReady > curTick() &&
170                cache->ticksToCycles(blk->whenReady - curTick()) >
171                accessLatency) {
172                lat = cache->ticksToCycles(blk->whenReady - curTick()) +
173                accessLatency;
174            }
175
176            // Update number of references to accessed block
177            blk->refCount++;
178
179            // Update replacement data of accessed block
180            replacementPolicy->touch(blk->replacementData);
181        } else {
182            // If a cache miss
183            lat = lookupLatency;
184        }
185
186        return blk;
187    }
188
189    /**
190     * Finds the given address in the cache, do not update replacement data.
191     * i.e. This is a no-side-effect find of a block.
192     * @param addr The address to find.
193     * @param is_secure True if the target memory space is secure.
194     * @param asid The address space ID.
195     * @return Pointer to the cache block if found.
196     */
197    CacheBlk* findBlock(Addr addr, bool is_secure) const override;
198
199    /**
200     * Find replacement victim based on address.
201     *
202     * @param addr Address to find a victim for.
203     * @return Cache block to be replaced.
204     */
205    CacheBlk* findVictim(Addr addr) override
206    {
207        // Get possible locations for the victim block
208        std::vector<CacheBlk*> locations = getPossibleLocations(addr);
209
210        // Choose replacement victim from replacement candidates
211        CacheBlk* victim = static_cast<CacheBlk*>(replacementPolicy->getVictim(
212                               std::vector<ReplaceableEntry*>(
213                                   locations.begin(), locations.end())));
214
215        DPRINTF(CacheRepl, "set %x, way %x: selecting blk for replacement\n",
216            victim->set, victim->way);
217
218        return victim;
219    }
220
221    /**
222     * Find all possible block locations for insertion and replacement of
223     * an address. Should be called immediately before ReplacementPolicy's
224     * findVictim() not to break cache resizing.
225     * Returns blocks in all ways belonging to the set of the address.
226     *
227     * @param addr The addr to a find possible locations for.
228     * @return The possible locations.
229     */
230    const std::vector<CacheBlk*> getPossibleLocations(Addr addr)
231    {
232        return sets[extractSet(addr)].blks;
233    }
234
235    /**
236     * Insert the new block into the cache and update replacement data.
237     *
238     * @param pkt Packet holding the address to update
239     * @param blk The block to update.
240     */
241    void insertBlock(PacketPtr pkt, CacheBlk *blk) override
242    {
243        // Insert block
244        BaseTags::insertBlock(pkt, blk);
245
246        // Update replacement policy
247        replacementPolicy->reset(blk->replacementData);
248    }
249
250    /**
251     * Limit the allocation for the cache ways.
252     * @param ways The maximum number of ways available for replacement.
253     */
254    virtual void setWayAllocationMax(int ways) override
255    {
256        fatal_if(ways < 1, "Allocation limit must be greater than zero");
257        allocAssoc = ways;
258    }
259
260    /**
261     * Get the way allocation mask limit.
262     * @return The maximum number of ways available for replacement.
263     */
264    virtual int getWayAllocationMax() const override
265    {
266        return allocAssoc;
267    }
268
269    /**
270     * Generate the tag from the given address.
271     * @param addr The address to get the tag from.
272     * @return The tag of the address.
273     */
274    Addr extractTag(Addr addr) const override
275    {
276        return (addr >> tagShift);
277    }
278
279    /**
280     * Calculate the set index from the address.
281     * @param addr The address to get the set from.
282     * @return The set index of the address.
283     */
284    int extractSet(Addr addr) const override
285    {
286        return ((addr >> setShift) & setMask);
287    }
288
289    /**
290     * Regenerate the block address from the tag and set.
291     *
292     * @param block The block.
293     * @return the block address.
294     */
295    Addr regenerateBlkAddr(const CacheBlk* blk) const override
296    {
297        return ((blk->tag << tagShift) | ((Addr)blk->set << setShift));
298    }
299
300    /**
301     * Called at end of simulation to complete average block reference stats.
302     */
303    void cleanupRefs() override;
304
305    /**
306     * Print all tags used
307     */
308    std::string print() const override;
309
310    /**
311     * Called prior to dumping stats to compute task occupancy
312     */
313    void computeStats() override;
314
315    /**
316     * Visit each block in the tag store and apply a visitor to the
317     * block.
318     *
319     * The visitor should be a function (or object that behaves like a
320     * function) that takes a cache block reference as its parameter
321     * and returns a bool. A visitor can request the traversal to be
322     * stopped by returning false, returning true causes it to be
323     * called for the next block in the tag store.
324     *
325     * \param visitor Visitor to call on each block.
326     */
327    void forEachBlk(CacheBlkVisitor &visitor) override {
328        for (CacheBlk& blk : blks) {
329            if (!visitor(blk))
330                return;
331        }
332    }
333};
334
335#endif //__MEM_CACHE_TAGS_BASE_SET_ASSOC_HH__
336