base_set_assoc.hh revision 13215 
1/*
2 * Copyright (c) 2012-2014,2017 ARM Limited
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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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26 * this software without specific prior written permission.
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     * This function updates the tags when a block is invalidated. It also
125     * updates the replacement data.
126     *
127     * @param blk The block to invalidate.
128     */
129    void invalidate(CacheBlk *blk) override;
130
131    /**
132     * Access block and update replacement data. May not succeed, in which case
133     * nullptr is returned. This has all the implications of a cache
134     * access and should only be used as such. Returns the access latency as a
135     * side effect.
136     * @param addr The address to find.
137     * @param is_secure True if the target memory space is secure.
138     * @param lat The access latency.
139     * @return Pointer to the cache block if found.
140     */
141    CacheBlk* accessBlock(Addr addr, bool is_secure, Cycles &lat) override
142    {
143        BlkType *blk = findBlock(addr, is_secure);
144
145        // Access all tags in parallel, hence one in each way.  The data side
146        // either accesses all blocks in parallel, or one block sequentially on
147        // a hit.  Sequential access with a miss doesn't access data.
148        tagAccesses += allocAssoc;
149        if (sequentialAccess) {
150            if (blk != nullptr) {
151                dataAccesses += 1;
152            }
153        } else {
154            dataAccesses += allocAssoc;
155        }
156
157        if (blk != nullptr) {
158            // If a cache hit
159            lat = accessLatency;
160            // Check if the block to be accessed is available. If not,
161            // apply the accessLatency on top of block->whenReady.
162            if (blk->whenReady > curTick() &&
163                cache->ticksToCycles(blk->whenReady - curTick()) >
164                accessLatency) {
165                lat = cache->ticksToCycles(blk->whenReady - curTick()) +
166                accessLatency;
167            }
168
169            // Update number of references to accessed block
170            blk->refCount++;
171
172            // Update replacement data of accessed block
173            replacementPolicy->touch(blk->replacementData);
174        } else {
175            // If a cache miss
176            lat = lookupLatency;
177        }
178
179        return blk;
180    }
181
182    /**
183     * Finds the given address in the cache, do not update replacement data.
184     * i.e. This is a no-side-effect find of a block.
185     *
186     * @param addr The address to find.
187     * @param is_secure True if the target memory space is secure.
188     * @return Pointer to the cache block if found.
189     */
190    CacheBlk* findBlock(Addr addr, bool is_secure) const override;
191
192    /**
193     * Find a block given set and way.
194     *
195     * @param set The set of the block.
196     * @param way The way of the block.
197     * @return The block.
198     */
199    ReplaceableEntry* findBlockBySetAndWay(int set, int way) const override;
200
201    /**
202     * Find replacement victim based on address. The list of evicted blocks
203     * only contains the victim.
204     *
205     * @param addr Address to find a victim for.
206     * @param is_secure True if the target memory space is secure.
207     * @param evict_blks Cache blocks to be evicted.
208     * @return Cache block to be replaced.
209     */
210    CacheBlk* findVictim(Addr addr, const bool is_secure,
211                         std::vector<CacheBlk*>& evict_blks) const override
212    {
213        // Get possible locations for the victim block
214        std::vector<CacheBlk*> locations = getPossibleLocations(addr);
215
216        // Choose replacement victim from replacement candidates
217        CacheBlk* victim = static_cast<CacheBlk*>(replacementPolicy->getVictim(
218                               std::vector<ReplaceableEntry*>(
219                                   locations.begin(), locations.end())));
220
221        // There is only one eviction for this replacement
222        evict_blks.push_back(victim);
223
224        DPRINTF(CacheRepl, "set %x, way %x: selecting blk for replacement\n",
225            victim->set, victim->way);
226
227        return victim;
228    }
229
230    /**
231     * Find all possible block locations for insertion and replacement of
232     * an address. Should be called immediately before ReplacementPolicy's
233     * findVictim() not to break cache resizing.
234     * Returns blocks in all ways belonging to the set of the address.
235     *
236     * @param addr The addr to a find possible locations for.
237     * @return The possible locations.
238     */
239    virtual const std::vector<CacheBlk*> getPossibleLocations(Addr addr) const
240    {
241        return sets[extractSet(addr)].blks;
242    }
243
244    /**
245     * Insert the new block into the cache and update replacement data.
246     *
247     * @param addr Address of the block.
248     * @param is_secure Whether the block is in secure space or not.
249     * @param src_master_ID The source requestor ID.
250     * @param task_ID The new task ID.
251     * @param blk The block to update.
252     */
253    void insertBlock(const Addr addr, const bool is_secure,
254                     const int src_master_ID, const uint32_t task_ID,
255                     CacheBlk *blk) override
256    {
257        // Insert block
258        BaseTags::insertBlock(addr, is_secure, src_master_ID, task_ID, blk);
259
260        // Increment tag counter
261        tagsInUse++;
262
263        // Update replacement policy
264        replacementPolicy->reset(blk->replacementData);
265    }
266
267    /**
268     * Limit the allocation for the cache ways.
269     * @param ways The maximum number of ways available for replacement.
270     */
271    virtual void setWayAllocationMax(int ways) override
272    {
273        fatal_if(ways < 1, "Allocation limit must be greater than zero");
274        allocAssoc = ways;
275    }
276
277    /**
278     * Get the way allocation mask limit.
279     * @return The maximum number of ways available for replacement.
280     */
281    virtual int getWayAllocationMax() const override
282    {
283        return allocAssoc;
284    }
285
286    /**
287     * Generate the tag from the given address.
288     * @param addr The address to get the tag from.
289     * @return The tag of the address.
290     */
291    Addr extractTag(Addr addr) const override
292    {
293        return (addr >> tagShift);
294    }
295
296    /**
297     * Regenerate the block address from the tag and set.
298     *
299     * @param block The block.
300     * @return the block address.
301     */
302    Addr regenerateBlkAddr(const CacheBlk* blk) const override
303    {
304        return ((blk->tag << tagShift) | ((Addr)blk->set << setShift));
305    }
306
307    void forEachBlk(std::function<void(CacheBlk &)> visitor) override {
308        for (CacheBlk& blk : blks) {
309            visitor(blk);
310        }
311    }
312
313    bool anyBlk(std::function<bool(CacheBlk &)> visitor) override {
314        for (CacheBlk& blk : blks) {
315            if (visitor(blk)) {
316                return true;
317            }
318        }
319        return false;
320    }
321
322  private:
323    /**
324     * Calculate the set index from the address.
325     *
326     * @param addr The address to get the set from.
327     * @return The set index of the address.
328     */
329    int extractSet(Addr addr) const
330    {
331        return ((addr >> setShift) & setMask);
332    }
333};
334
335#endif //__MEM_CACHE_TAGS_BASE_SET_ASSOC_HH__
336