base_set_assoc.hh revision 13216 
1/*
2 * Copyright (c) 2012-2014,2017 ARM Limited
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4 *
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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.
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18 * modification, are permitted provided that the following conditions are
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27 *
28 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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33 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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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 <functional>
52#include <string>
53#include <vector>
54
55#include "base/logging.hh"
56#include "base/types.hh"
57#include "debug/CacheRepl.hh"
58#include "mem/cache/base.hh"
59#include "mem/cache/blk.hh"
60#include "mem/cache/replacement_policies/base.hh"
61#include "mem/cache/tags/base.hh"
62#include "mem/cache/tags/cacheset.hh"
63#include "params/BaseSetAssoc.hh"
64
65/**
66 * A BaseSetAssoc cache tag store.
67 * @sa  \ref gem5MemorySystem "gem5 Memory System"
68 *
69 * The BaseSetAssoc placement policy divides the cache into s sets of w
70 * cache lines (ways). A cache line is mapped onto a set, and can be placed
71 * into any of the ways of this set.
72 */
73class BaseSetAssoc : public BaseTags
74{
75  public:
76    /** Typedef the block type used in this tag store. */
77    typedef CacheBlk BlkType;
78    /** Typedef the set type used in this tag store. */
79    typedef CacheSet<CacheBlk> SetType;
80
81  protected:
82    /** The associativity of the cache. */
83    const unsigned assoc;
84    /** The allocatable associativity of the cache (alloc mask). */
85    unsigned allocAssoc;
86
87    /** The cache blocks. */
88    std::vector<BlkType> blks;
89
90    /** The number of sets in the cache. */
91    const unsigned numSets;
92
93    /** Whether tags and data are accessed sequentially. */
94    const bool sequentialAccess;
95
96    /** The cache sets. */
97    std::vector<SetType> sets;
98
99    /** The amount to shift the address to get the set. */
100    int setShift;
101    /** The amount to shift the address to get the tag. */
102    int tagShift;
103    /** Mask out all bits that aren't part of the set index. */
104    unsigned setMask;
105
106    /** Replacement policy */
107    BaseReplacementPolicy *replacementPolicy;
108
109  public:
110    /** Convenience typedef. */
111     typedef BaseSetAssocParams Params;
112
113    /**
114     * Construct and initialize this tag store.
115     */
116    BaseSetAssoc(const Params *p);
117
118    /**
119     * Destructor
120     */
121    virtual ~BaseSetAssoc() {};
122
123    /**
124     * Initialize blocks and set the parent cache back pointer.
125     *
126     * @param _cache Pointer to parent cache.
127     */
128    void init(BaseCache *_cache) override;
129
130    /**
131     * This function updates the tags when a block is invalidated. It also
132     * updates the replacement data.
133     *
134     * @param blk The block to invalidate.
135     */
136    void invalidate(CacheBlk *blk) 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     *
193     * @param addr The address to find.
194     * @param is_secure True if the target memory space is secure.
195     * @return Pointer to the cache block if found.
196     */
197    CacheBlk* findBlock(Addr addr, bool is_secure) const override;
198
199    /**
200     * Find a block given set and way.
201     *
202     * @param set The set of the block.
203     * @param way The way of the block.
204     * @return The block.
205     */
206    ReplaceableEntry* findBlockBySetAndWay(int set, int way) const override;
207
208    /**
209     * Find replacement victim based on address. The list of evicted blocks
210     * only contains the victim.
211     *
212     * @param addr Address to find a victim for.
213     * @param is_secure True if the target memory space is secure.
214     * @param evict_blks Cache blocks to be evicted.
215     * @return Cache block to be replaced.
216     */
217    CacheBlk* findVictim(Addr addr, const bool is_secure,
218                         std::vector<CacheBlk*>& evict_blks) const override
219    {
220        // Get possible locations for the victim block
221        std::vector<CacheBlk*> locations = getPossibleLocations(addr);
222
223        // Choose replacement victim from replacement candidates
224        CacheBlk* victim = static_cast<CacheBlk*>(replacementPolicy->getVictim(
225                               std::vector<ReplaceableEntry*>(
226                                   locations.begin(), locations.end())));
227
228        // There is only one eviction for this replacement
229        evict_blks.push_back(victim);
230
231        DPRINTF(CacheRepl, "set %x, way %x: selecting blk for replacement\n",
232            victim->set, victim->way);
233
234        return victim;
235    }
236
237    /**
238     * Find all possible block locations for insertion and replacement of
239     * an address. Should be called immediately before ReplacementPolicy's
240     * findVictim() not to break cache resizing.
241     * Returns blocks in all ways belonging to the set of the address.
242     *
243     * @param addr The addr to a find possible locations for.
244     * @return The possible locations.
245     */
246    virtual const std::vector<CacheBlk*> getPossibleLocations(Addr addr) const
247    {
248        return sets[extractSet(addr)].blks;
249    }
250
251    /**
252     * Insert the new block into the cache and update replacement data.
253     *
254     * @param addr Address of the block.
255     * @param is_secure Whether the block is in secure space or not.
256     * @param src_master_ID The source requestor ID.
257     * @param task_ID The new task ID.
258     * @param blk The block to update.
259     */
260    void insertBlock(const Addr addr, const bool is_secure,
261                     const int src_master_ID, const uint32_t task_ID,
262                     CacheBlk *blk) override
263    {
264        // Insert block
265        BaseTags::insertBlock(addr, is_secure, src_master_ID, task_ID, blk);
266
267        // Increment tag counter
268        tagsInUse++;
269
270        // Update replacement policy
271        replacementPolicy->reset(blk->replacementData);
272    }
273
274    /**
275     * Limit the allocation for the cache ways.
276     * @param ways The maximum number of ways available for replacement.
277     */
278    virtual void setWayAllocationMax(int ways) override
279    {
280        fatal_if(ways < 1, "Allocation limit must be greater than zero");
281        allocAssoc = ways;
282    }
283
284    /**
285     * Get the way allocation mask limit.
286     * @return The maximum number of ways available for replacement.
287     */
288    virtual int getWayAllocationMax() const override
289    {
290        return allocAssoc;
291    }
292
293    /**
294     * Generate the tag from the given address.
295     * @param addr The address to get the tag from.
296     * @return The tag of the address.
297     */
298    Addr extractTag(Addr addr) const override
299    {
300        return (addr >> tagShift);
301    }
302
303    /**
304     * Regenerate the block address from the tag and set.
305     *
306     * @param block The block.
307     * @return the block address.
308     */
309    Addr regenerateBlkAddr(const CacheBlk* blk) const override
310    {
311        return ((blk->tag << tagShift) | ((Addr)blk->set << setShift));
312    }
313
314    void forEachBlk(std::function<void(CacheBlk &)> visitor) override {
315        for (CacheBlk& blk : blks) {
316            visitor(blk);
317        }
318    }
319
320    bool anyBlk(std::function<bool(CacheBlk &)> visitor) override {
321        for (CacheBlk& blk : blks) {
322            if (visitor(blk)) {
323                return true;
324            }
325        }
326        return false;
327    }
328
329  private:
330    /**
331     * Calculate the set index from the address.
332     *
333     * @param addr The address to get the set from.
334     * @return The set index of the address.
335     */
336    int extractSet(Addr addr) const
337    {
338        return ((addr >> setShift) & setMask);
339    }
340};
341
342#endif //__MEM_CACHE_TAGS_BASE_SET_ASSOC_HH__
343