base_set_assoc.hh revision 13218 
1/*
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13 *
14 * Copyright (c) 2003-2005,2014 The Regents of The University of Michigan
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28 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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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 "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 std::vector<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    /**
109     * Find all possible block locations for insertion and replacement of
110     * an address. Should be called immediately before ReplacementPolicy's
111     * findVictim() not to break cache resizing.
112     * Returns blocks in all ways belonging to the set of the address.
113     *
114     * @param addr The addr to a find possible locations for.
115     * @return The possible locations.
116     */
117    std::vector<ReplaceableEntry*> getPossibleLocations(const Addr addr) const
118                                                                      override
119    {
120        std::vector<ReplaceableEntry*> locations;
121        for (const auto& blk : sets[extractSet(addr)]) {
122            locations.push_back(static_cast<ReplaceableEntry*>(blk));
123        }
124        return locations;
125    }
126
127  public:
128    /** Convenience typedef. */
129     typedef BaseSetAssocParams Params;
130
131    /**
132     * Construct and initialize this tag store.
133     */
134    BaseSetAssoc(const Params *p);
135
136    /**
137     * Destructor
138     */
139    virtual ~BaseSetAssoc() {};
140
141    /**
142     * Initialize blocks and set the parent cache back pointer.
143     *
144     * @param _cache Pointer to parent cache.
145     */
146    void init(BaseCache *_cache) override;
147
148    /**
149     * This function updates the tags when a block is invalidated. It also
150     * updates the replacement data.
151     *
152     * @param blk The block to invalidate.
153     */
154    void invalidate(CacheBlk *blk) override;
155
156    /**
157     * Access block and update replacement data. May not succeed, in which case
158     * nullptr is returned. This has all the implications of a cache
159     * access and should only be used as such. Returns the access latency as a
160     * side effect.
161     * @param addr The address to find.
162     * @param is_secure True if the target memory space is secure.
163     * @param lat The access latency.
164     * @return Pointer to the cache block if found.
165     */
166    CacheBlk* accessBlock(Addr addr, bool is_secure, Cycles &lat) override
167    {
168        BlkType *blk = findBlock(addr, is_secure);
169
170        // Access all tags in parallel, hence one in each way.  The data side
171        // either accesses all blocks in parallel, or one block sequentially on
172        // a hit.  Sequential access with a miss doesn't access data.
173        tagAccesses += allocAssoc;
174        if (sequentialAccess) {
175            if (blk != nullptr) {
176                dataAccesses += 1;
177            }
178        } else {
179            dataAccesses += allocAssoc;
180        }
181
182        if (blk != nullptr) {
183            // If a cache hit
184            lat = accessLatency;
185            // Check if the block to be accessed is available. If not,
186            // apply the accessLatency on top of block->whenReady.
187            if (blk->whenReady > curTick() &&
188                cache->ticksToCycles(blk->whenReady - curTick()) >
189                accessLatency) {
190                lat = cache->ticksToCycles(blk->whenReady - curTick()) +
191                accessLatency;
192            }
193
194            // Update number of references to accessed block
195            blk->refCount++;
196
197            // Update replacement data of accessed block
198            replacementPolicy->touch(blk->replacementData);
199        } else {
200            // If a cache miss
201            lat = lookupLatency;
202        }
203
204        return blk;
205    }
206
207    /**
208     * Find a block given set and way.
209     *
210     * @param set The set of the block.
211     * @param way The way of the block.
212     * @return The block.
213     */
214    ReplaceableEntry* findBlockBySetAndWay(int set, int way) const override;
215
216    /**
217     * Find replacement victim based on address. The list of evicted blocks
218     * only contains the victim.
219     *
220     * @param addr Address to find a victim for.
221     * @param is_secure True if the target memory space is secure.
222     * @param evict_blks Cache blocks to be evicted.
223     * @return Cache block to be replaced.
224     */
225    CacheBlk* findVictim(Addr addr, const bool is_secure,
226                         std::vector<CacheBlk*>& evict_blks) const override
227    {
228        // Get possible locations for the victim block
229        std::vector<ReplaceableEntry*> locations = getPossibleLocations(addr);
230
231        // Choose replacement victim from replacement candidates
232        CacheBlk* victim = static_cast<CacheBlk*>(replacementPolicy->getVictim(
233                               std::vector<ReplaceableEntry*>(
234                                   locations.begin(), locations.end())));
235
236        // There is only one eviction for this replacement
237        evict_blks.push_back(victim);
238
239        DPRINTF(CacheRepl, "set %x, way %x: selecting blk for replacement\n",
240                victim->getSet(), victim->getWay());
241
242        return victim;
243    }
244
245    /**
246     * Insert the new block into the cache and update replacement data.
247     *
248     * @param addr Address of the block.
249     * @param is_secure Whether the block is in secure space or not.
250     * @param src_master_ID The source requestor ID.
251     * @param task_ID The new task ID.
252     * @param blk The block to update.
253     */
254    void insertBlock(const Addr addr, const bool is_secure,
255                     const int src_master_ID, const uint32_t task_ID,
256                     CacheBlk *blk) override
257    {
258        // Insert block
259        BaseTags::insertBlock(addr, is_secure, src_master_ID, task_ID, blk);
260
261        // Increment tag counter
262        tagsInUse++;
263
264        // Update replacement policy
265        replacementPolicy->reset(blk->replacementData);
266    }
267
268    /**
269     * Limit the allocation for the cache ways.
270     * @param ways The maximum number of ways available for replacement.
271     */
272    virtual void setWayAllocationMax(int ways) override
273    {
274        fatal_if(ways < 1, "Allocation limit must be greater than zero");
275        allocAssoc = ways;
276    }
277
278    /**
279     * Get the way allocation mask limit.
280     * @return The maximum number of ways available for replacement.
281     */
282    virtual int getWayAllocationMax() const override
283    {
284        return allocAssoc;
285    }
286
287    /**
288     * Generate the tag from the given address.
289     * @param addr The address to get the tag from.
290     * @return The tag of the address.
291     */
292    Addr extractTag(Addr addr) const override
293    {
294        return (addr >> tagShift);
295    }
296
297    /**
298     * Regenerate the block address from the tag and set.
299     *
300     * @param block The block.
301     * @return the block address.
302     */
303    Addr regenerateBlkAddr(const CacheBlk* blk) const override
304    {
305        const Addr set = blk->getSet() << setShift;
306        return ((blk->tag << tagShift) | set);
307    }
308
309    void forEachBlk(std::function<void(CacheBlk &)> visitor) override {
310        for (CacheBlk& blk : blks) {
311            visitor(blk);
312        }
313    }
314
315    bool anyBlk(std::function<bool(CacheBlk &)> visitor) override {
316        for (CacheBlk& blk : blks) {
317            if (visitor(blk)) {
318                return true;
319            }
320        }
321        return false;
322    }
323
324  private:
325    /**
326     * Calculate the set index from the address.
327     *
328     * @param addr The address to get the set from.
329     * @return The set index of the address.
330     */
331    int extractSet(Addr addr) const
332    {
333        return ((addr >> setShift) & setMask);
334    }
335};
336
337#endif //__MEM_CACHE_TAGS_BASE_SET_ASSOC_HH__
338