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

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

#include "base/logging.hh"
#include "base/types.hh"
#include "debug/CacheRepl.hh"
#include "mem/cache/base.hh"
#include "mem/cache/blk.hh"
#include "mem/cache/replacement_policies/base.hh"
#include "mem/cache/tags/base.hh"
#include "params/BaseSetAssoc.hh"

/**
 * A BaseSetAssoc cache tag store.
 * @sa  \ref gem5MemorySystem "gem5 Memory System"
 *
 * The BaseSetAssoc placement policy divides the cache into s sets of w
 * cache lines (ways). A cache line is mapped onto a set, and can be placed
 * into any of the ways of this set.
 */
class BaseSetAssoc : public BaseTags
{
  public:
    /** Typedef the block type used in this tag store. */
    typedef CacheBlk BlkType;
    /** Typedef the set type used in this tag store. */
    typedef std::vector<CacheBlk*> SetType;

  protected:
    /** The associativity of the cache. */
    const unsigned assoc;
    /** The allocatable associativity of the cache (alloc mask). */
    unsigned allocAssoc;

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

    /** The number of sets in the cache. */
    const unsigned numSets;

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

    /** The cache sets. */
    std::vector<SetType> sets;

    /** The amount to shift the address to get the set. */
    int setShift;
    /** The amount to shift the address to get the tag. */
    int tagShift;
    /** Mask out all bits that aren't part of the set index. */
    unsigned setMask;

    /** Replacement policy */
    BaseReplacementPolicy *replacementPolicy;

    /**
     * Find all possible block locations for insertion and replacement of
     * an address. Should be called immediately before ReplacementPolicy's
     * findVictim() not to break cache resizing.
     * Returns blocks in all ways belonging to the set of the address.
     *
     * @param addr The addr to a find possible locations for.
     * @return The possible locations.
     */
    std::vector<ReplaceableEntry*> getPossibleLocations(const Addr addr) const
                                                                      override
    {
        std::vector<ReplaceableEntry*> locations;
        for (const auto& blk : sets[extractSet(addr)]) {
            locations.push_back(static_cast<ReplaceableEntry*>(blk));
        }
        return locations;
    }

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

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

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

    /**
     * Initialize blocks and set the parent cache back pointer.
     *
     * @param _cache Pointer to parent cache.
     */
    void init(BaseCache *_cache) 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 access 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 access latency.
     * @return Pointer to the cache block if found.
     */
    CacheBlk* accessBlock(Addr addr, bool is_secure, Cycles &lat) override
    {
        BlkType *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 (blk != nullptr) {
            // If a cache hit
            lat = accessLatency;
            // Check if the block to be accessed is available. If not,
            // apply the accessLatency on top of block->whenReady.
            if (blk->whenReady > curTick() &&
                cache->ticksToCycles(blk->whenReady - curTick()) >
                accessLatency) {
                lat = cache->ticksToCycles(blk->whenReady - curTick()) +
                accessLatency;
            }

            // Update number of references to accessed block
            blk->refCount++;

            // Update replacement data of accessed block
            replacementPolicy->touch(blk->replacementData);
        } else {
            // If a cache miss
            lat = lookupLatency;
        }

        return blk;
    }

    /**
     * Find a block given set and way.
     *
     * @param set The set of the block.
     * @param way The way of the block.
     * @return The block.
     */
    ReplaceableEntry* findBlockBySetAndWay(int set, int way) const override;

    /**
     * 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 evict_blks Cache blocks to be evicted.
     * @return Cache block to be replaced.
     */
    CacheBlk* findVictim(Addr addr, const bool is_secure,
                         std::vector<CacheBlk*>& evict_blks) const override
    {
        // Get possible locations for the victim block
        std::vector<ReplaceableEntry*> locations = getPossibleLocations(addr);

        // Choose replacement victim from replacement candidates
        CacheBlk* victim = static_cast<CacheBlk*>(replacementPolicy->getVictim(
                               std::vector<ReplaceableEntry*>(
                                   locations.begin(), locations.end())));

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

        DPRINTF(CacheRepl, "set %x, way %x: selecting blk for replacement\n",
                victim->getSet(), victim->getWay());

        return victim;
    }

    /**
     * Insert the new block into the cache and update replacement data.
     *
     * @param addr Address of the block.
     * @param is_secure Whether the block is in secure space or not.
     * @param src_master_ID The source requestor ID.
     * @param task_ID The new task ID.
     * @param blk The block to update.
     */
    void insertBlock(const Addr addr, const bool is_secure,
                     const int src_master_ID, const uint32_t task_ID,
                     CacheBlk *blk) override
    {
        // Insert block
        BaseTags::insertBlock(addr, is_secure, src_master_ID, task_ID, 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;
    }

    /**
     * Generate the tag from the given address.
     * @param addr The address to get the tag from.
     * @return The tag of the address.
     */
    Addr extractTag(Addr addr) const override
    {
        return (addr >> tagShift);
    }

    /**
     * Regenerate the block address from the tag and set.
     *
     * @param block The block.
     * @return the block address.
     */
    Addr regenerateBlkAddr(const CacheBlk* blk) const override
    {
        const Addr set = blk->getSet() << setShift;
        return ((blk->tag << tagShift) | set);
    }

    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;
    }

  private:
    /**
     * Calculate the set index from the address.
     *
     * @param addr The address to get the set from.
     * @return The set index of the address.
     */
    int extractSet(Addr addr) const
    {
        return ((addr >> setShift) & setMask);
    }
};

#endif //__MEM_CACHE_TAGS_BASE_SET_ASSOC_HH__