xref: /gem5/src/mem/cache/tags/base_set_assoc.hh

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 * All rights reserved.
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 * met: redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer;
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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 * Authors: Erik Hallnor
 */

/**
 * @file
 * Declaration of a base set associative tag store.
 */

#ifndef __MEM_CACHE_TAGS_BASE_SET_ASSOC_HH__
#define __MEM_CACHE_TAGS_BASE_SET_ASSOC_HH__

#include <cstdint>
#include <functional>
#include <string>
#include <vector>

#include "base/logging.hh"
#include "base/types.hh"
#include "mem/cache/base.hh"
#include "mem/cache/cache_blk.hh"
#include "mem/cache/replacement_policies/base.hh"
#include "mem/cache/replacement_policies/replaceable_entry.hh"
#include "mem/cache/tags/base.hh"
#include "mem/cache/tags/indexing_policies/base.hh"
#include "mem/packet.hh"
#include "params/BaseSetAssoc.hh"

/**
 * A basic cache tag store.
 * @sa  \ref gem5MemorySystem "gem5 Memory System"
 *
 * The BaseSetAssoc placement policy divides the cache into s sets of w
 * cache lines (ways).
 */
class BaseSetAssoc : public BaseTags
{
  protected:
    /** The allocatable associativity of the cache (alloc mask). */
    unsigned allocAssoc;

    /** The cache blocks. */
    std::vector<CacheBlk> blks;

    /** Whether tags and data are accessed sequentially. */
    const bool sequentialAccess;

    /** Replacement policy */
    BaseReplacementPolicy *replacementPolicy;

  public:
    /** Convenience typedef. */
     typedef BaseSetAssocParams Params;

    /**
     * Construct and initialize this tag store.
     */
    BaseSetAssoc(const Params *p);

    /**
     * Destructor
     */
    virtual ~BaseSetAssoc() {};

    /**
     * Initialize blocks as CacheBlk instances.
     */
    void tagsInit() override;

    /**
     * This function updates the tags when a block is invalidated. It also
     * updates the replacement data.
     *
     * @param blk The block to invalidate.
     */
    void invalidate(CacheBlk *blk) override;

    /**
     * Access block and update replacement data. May not succeed, in which case
     * nullptr is returned. This has all the implications of a cache access and
     * should only be used as such. Returns the tag lookup latency as a side
     * effect.
     *
     * @param addr The address to find.
     * @param is_secure True if the target memory space is secure.
     * @param lat The latency of the tag lookup.
     * @return Pointer to the cache block if found.
     */
    CacheBlk* accessBlock(Addr addr, bool is_secure, Cycles &lat) override
    {
        CacheBlk *blk = findBlock(addr, is_secure);

        // Access all tags in parallel, hence one in each way.  The data side
        // either accesses all blocks in parallel, or one block sequentially on
        // a hit.  Sequential access with a miss doesn't access data.
        tagAccesses += allocAssoc;
        if (sequentialAccess) {
            if (blk != nullptr) {
                dataAccesses += 1;
            }
        } else {
            dataAccesses += allocAssoc;
        }

        // If a cache hit
        if (blk != nullptr) {
            // Update number of references to accessed block
            blk->refCount++;

            // Update replacement data of accessed block
            replacementPolicy->touch(blk->replacementData);
        }

        // The tag lookup latency is the same for a hit or a miss
        lat = lookupLatency;

        return blk;
    }

    /**
     * Find replacement victim based on address. The list of evicted blocks
     * only contains the victim.
     *
     * @param addr Address to find a victim for.
     * @param is_secure True if the target memory space is secure.
     * @param size Size, in bits, of new block to allocate.
     * @param evict_blks Cache blocks to be evicted.
     * @return Cache block to be replaced.
     */
    CacheBlk* findVictim(Addr addr, const bool is_secure,
                         const std::size_t size,
                         std::vector<CacheBlk*>& evict_blks) const override
    {
        // Get possible entries to be victimized
        const std::vector<ReplaceableEntry*> entries =
            indexingPolicy->getPossibleEntries(addr);

        // Choose replacement victim from replacement candidates
        CacheBlk* victim = static_cast<CacheBlk*>(replacementPolicy->getVictim(
                                entries));

        // There is only one eviction for this replacement
        evict_blks.push_back(victim);

        return victim;
    }

    /**
     * Insert the new block into the cache and update replacement data.
     *
     * @param pkt Packet holding the address to update
     * @param blk The block to update.
     */
    void insertBlock(const PacketPtr pkt, CacheBlk *blk) override
    {
        // Insert block
        BaseTags::insertBlock(pkt, blk);

        // Increment tag counter
        tagsInUse++;

        // Update replacement policy
        replacementPolicy->reset(blk->replacementData);
    }

    /**
     * Limit the allocation for the cache ways.
     * @param ways The maximum number of ways available for replacement.
     */
    virtual void setWayAllocationMax(int ways) override
    {
        fatal_if(ways < 1, "Allocation limit must be greater than zero");
        allocAssoc = ways;
    }

    /**
     * Get the way allocation mask limit.
     * @return The maximum number of ways available for replacement.
     */
    virtual int getWayAllocationMax() const override
    {
        return allocAssoc;
    }

    /**
     * Regenerate the block address from the tag and indexing location.
     *
     * @param block The block.
     * @return the block address.
     */
    Addr regenerateBlkAddr(const CacheBlk* blk) const override
    {
        return indexingPolicy->regenerateAddr(blk->tag, blk);
    }

    void forEachBlk(std::function<void(CacheBlk &)> visitor) override {
        for (CacheBlk& blk : blks) {
            visitor(blk);
        }
    }

    bool anyBlk(std::function<bool(CacheBlk &)> visitor) override {
        for (CacheBlk& blk : blks) {
            if (visitor(blk)) {
                return true;
            }
        }
        return false;
    }
};

#endif //__MEM_CACHE_TAGS_BASE_SET_ASSOC_HH__