gem5/src/mem/cache/cache.hh

/*
 * Copyright (c) 2012-2016 ARM Limited
 * All rights reserved.
 *
 * The license below extends only to copyright in the software and shall
 * not be construed as granting a license to any other intellectual
 * property including but not limited to intellectual property relating
 * to a hardware implementation of the functionality of the software
 * licensed hereunder.  You may use the software subject to the license
 * terms below provided that you ensure that this notice is replicated
 * unmodified and in its entirety in all distributions of the software,
 * modified or unmodified, in source code or in binary form.
 *
 * Copyright (c) 2002-2005 The Regents of The University of Michigan
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met: redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer;
 * redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution;
 * neither the name of the copyright holders nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Authors: Erik Hallnor
 *          Dave Greene
 *          Steve Reinhardt
 *          Ron Dreslinski
 *          Andreas Hansson
 */

/**
 * @file
 * Describes a cache based on template policies.
 */

#ifndef __MEM_CACHE_CACHE_HH__
#define __MEM_CACHE_CACHE_HH__

#include <unordered_set>

#include "base/misc.hh" // fatal, panic, and warn
#include "enums/Clusivity.hh"
#include "mem/cache/base.hh"
#include "mem/cache/blk.hh"
#include "mem/cache/mshr.hh"
#include "mem/cache/tags/base.hh"
#include "params/Cache.hh"
#include "sim/eventq.hh"

//Forward decleration
class BasePrefetcher;

/**
 * A template-policy based cache. The behavior of the cache can be altered by
 * supplying different template policies. TagStore handles all tag and data
 * storage @sa TagStore, \ref gem5MemorySystem "gem5 Memory System"
 */
class Cache : public BaseCache
{
  protected:

    /**
     * The CPU-side port extends the base cache slave port with access
     * functions for functional, atomic and timing requests.
     */
    class CpuSidePort : public CacheSlavePort
    {
      private:

        // a pointer to our specific cache implementation
        Cache *cache;

      protected:

        virtual bool recvTimingSnoopResp(PacketPtr pkt);

        virtual bool recvTimingReq(PacketPtr pkt);

        virtual Tick recvAtomic(PacketPtr pkt);

        virtual void recvFunctional(PacketPtr pkt);

        virtual AddrRangeList getAddrRanges() const;

      public:

        CpuSidePort(const std::string &_name, Cache *_cache,
                    const std::string &_label);

    };

    /**
     * Override the default behaviour of sendDeferredPacket to enable
     * the memory-side cache port to also send requests based on the
     * current MSHR status. This queue has a pointer to our specific
     * cache implementation and is used by the MemSidePort.
     */
    class CacheReqPacketQueue : public ReqPacketQueue
    {

      protected:

        Cache &cache;
        SnoopRespPacketQueue &snoopRespQueue;

      public:

        CacheReqPacketQueue(Cache &cache, MasterPort &port,
                            SnoopRespPacketQueue &snoop_resp_queue,
                            const std::string &label) :
            ReqPacketQueue(cache, port, label), cache(cache),
            snoopRespQueue(snoop_resp_queue) { }

        /**
         * Override the normal sendDeferredPacket and do not only
         * consider the transmit list (used for responses), but also
         * requests.
         */
        virtual void sendDeferredPacket();

        /**
         * Check if there is a conflicting snoop response about to be
         * send out, and if so simply stall any requests, and schedule
         * a send event at the same time as the next snoop response is
         * being sent out.
         */
        bool checkConflictingSnoop(Addr addr)
        {
            if (snoopRespQueue.hasAddr(addr)) {
                DPRINTF(CachePort, "Waiting for snoop response to be "
                        "sent\n");
                Tick when = snoopRespQueue.deferredPacketReadyTime();
                schedSendEvent(when);
                return true;
            }
            return false;
        }
    };

    /**
     * The memory-side port extends the base cache master port with
     * access functions for functional, atomic and timing snoops.
     */
    class MemSidePort : public CacheMasterPort
    {
      private:

        /** The cache-specific queue. */
        CacheReqPacketQueue _reqQueue;

        SnoopRespPacketQueue _snoopRespQueue;

        // a pointer to our specific cache implementation
        Cache *cache;

      protected:

        virtual void recvTimingSnoopReq(PacketPtr pkt);

        virtual bool recvTimingResp(PacketPtr pkt);

        virtual Tick recvAtomicSnoop(PacketPtr pkt);

        virtual void recvFunctionalSnoop(PacketPtr pkt);

      public:

        MemSidePort(const std::string &_name, Cache *_cache,
                    const std::string &_label);
    };

    /** Tag and data Storage */
    BaseTags *tags;

    /** Prefetcher */
    BasePrefetcher *prefetcher;

    /** Temporary cache block for occasional transitory use */
    CacheBlk *tempBlock;

    /**
     * This cache should allocate a block on a line-sized write miss.
     */
    const bool doFastWrites;

    /**
     * Turn line-sized writes into WriteInvalidate transactions.
     */
    void promoteWholeLineWrites(PacketPtr pkt);

    /**
     * Notify the prefetcher on every access, not just misses.
     */
    const bool prefetchOnAccess;

     /**
     * Clusivity with respect to the upstream cache, determining if we
     * fill into both this cache and the cache above on a miss. Note
     * that we currently do not support strict clusivity policies.
     */
    const Enums::Clusivity clusivity;

     /**
     * Determine if clean lines should be written back or not. In
     * cases where a downstream cache is mostly inclusive we likely
     * want it to act as a victim cache also for lines that have not
     * been modified. Hence, we cannot simply drop the line (or send a
     * clean evict), but rather need to send the actual data.
     */
    const bool writebackClean;

    /**
     * Upstream caches need this packet until true is returned, so
     * hold it for deletion until a subsequent call
     */
    std::unique_ptr<Packet> pendingDelete;

    /**
     * Writebacks from the tempBlock, resulting on the response path
     * in atomic mode, must happen after the call to recvAtomic has
     * finished (for the right ordering of the packets). We therefore
     * need to hold on to the packets, and have a method and an event
     * to send them.
     */
    PacketPtr tempBlockWriteback;

    /**
     * Send the outstanding tempBlock writeback. To be called after
     * recvAtomic finishes in cases where the block we filled is in
     * fact the tempBlock, and now needs to be written back.
     */
    void writebackTempBlockAtomic() {
        assert(tempBlockWriteback != nullptr);
        PacketList writebacks{tempBlockWriteback};
        doWritebacksAtomic(writebacks);
        tempBlockWriteback = nullptr;
    }

    /**
     * An event to writeback the tempBlock after recvAtomic
     * finishes. To avoid other calls to recvAtomic getting in
     * between, we create this event with a higher priority.
     */
    EventWrapper<Cache, &Cache::writebackTempBlockAtomic> \
        writebackTempBlockAtomicEvent;

    /**
     * Store the outstanding requests that we are expecting snoop
     * responses from so we can determine which snoop responses we
     * generated and which ones were merely forwarded.
     */
    std::unordered_set<RequestPtr> outstandingSnoop;

    /**
     * Does all the processing necessary to perform the provided request.
     * @param pkt The memory request to perform.
     * @param blk The cache block to be updated.
     * @param lat The latency of the access.
     * @param writebacks List for any writebacks that need to be performed.
     * @return Boolean indicating whether the request was satisfied.
     */
    bool access(PacketPtr pkt, CacheBlk *&blk,
                Cycles &lat, PacketList &writebacks);

    /**
     *Handle doing the Compare and Swap function for SPARC.
     */
    void cmpAndSwap(CacheBlk *blk, PacketPtr pkt);

    /**
     * Find a block frame for new block at address addr targeting the
     * given security space, assuming that the block is not currently
     * in the cache.  Append writebacks if any to provided packet
     * list.  Return free block frame.  May return nullptr if there are
     * no replaceable blocks at the moment.
     */
    CacheBlk *allocateBlock(Addr addr, bool is_secure, PacketList &writebacks);

    /**
     * Invalidate a cache block.
     *
     * @param blk Block to invalidate
     */
    void invalidateBlock(CacheBlk *blk);

    /**
     * Maintain the clusivity of this cache by potentially
     * invalidating a block. This method works in conjunction with
     * satisfyRequest, but is separate to allow us to handle all MSHR
     * targets before potentially dropping a block.
     *
     * @param from_cache Whether we have dealt with a packet from a cache
     * @param blk The block that should potentially be dropped
     */
    void maintainClusivity(bool from_cache, CacheBlk *blk);

    /**
     * Populates a cache block and handles all outstanding requests for the
     * satisfied fill request. This version takes two memory requests. One
     * contains the fill data, the other is an optional target to satisfy.
     * @param pkt The memory request with the fill data.
     * @param blk The cache block if it already exists.
     * @param writebacks List for any writebacks that need to be performed.
     * @param allocate Whether to allocate a block or use the temp block
     * @return Pointer to the new cache block.
     */
    CacheBlk *handleFill(PacketPtr pkt, CacheBlk *blk,
                         PacketList &writebacks, bool allocate);

    /**
     * Determine whether we should allocate on a fill or not. If this
     * cache is mostly inclusive with regards to the upstream cache(s)
     * we always allocate (for any non-forwarded and cacheable
     * requests). In the case of a mostly exclusive cache, we allocate
     * on fill if the packet did not come from a cache, thus if we:
     * are dealing with a whole-line write (the latter behaves much
     * like a writeback), the original target packet came from a
     * non-caching source, or if we are performing a prefetch or LLSC.
     *
     * @param cmd Command of the incoming requesting packet
     * @return Whether we should allocate on the fill
     */
    inline bool allocOnFill(MemCmd cmd) const override
    {
        return clusivity == Enums::mostly_incl ||
            cmd == MemCmd::WriteLineReq ||
            cmd == MemCmd::ReadReq ||
            cmd == MemCmd::WriteReq ||
            cmd.isPrefetch() ||
            cmd.isLLSC();
    }

    /**
     * Performs the access specified by the request.
     * @param pkt The request to perform.
     * @return The result of the access.
     */
    bool recvTimingReq(PacketPtr pkt);

    /**
     * Insert writebacks into the write buffer
     */
    void doWritebacks(PacketList& writebacks, Tick forward_time);

    /**
     * Send writebacks down the memory hierarchy in atomic mode
     */
    void doWritebacksAtomic(PacketList& writebacks);

    /**
     * Handling the special case of uncacheable write responses to
     * make recvTimingResp less cluttered.
     */
    void handleUncacheableWriteResp(PacketPtr pkt);

    /**
     * Handles a response (cache line fill/write ack) from the bus.
     * @param pkt The response packet
     */
    void recvTimingResp(PacketPtr pkt);

    /**
     * Snoops bus transactions to maintain coherence.
     * @param pkt The current bus transaction.
     */
    void recvTimingSnoopReq(PacketPtr pkt);

    /**
     * Handle a snoop response.
     * @param pkt Snoop response packet
     */
    void recvTimingSnoopResp(PacketPtr pkt);

    /**
     * Performs the access specified by the request.
     * @param pkt The request to perform.
     * @return The number of ticks required for the access.
     */
    Tick recvAtomic(PacketPtr pkt);

    /**
     * Snoop for the provided request in the cache and return the estimated
     * time taken.
     * @param pkt The memory request to snoop
     * @return The number of ticks required for the snoop.
     */
    Tick recvAtomicSnoop(PacketPtr pkt);

    /**
     * Performs the access specified by the request.
     * @param pkt The request to perform.
     * @param fromCpuSide from the CPU side port or the memory side port
     */
    void functionalAccess(PacketPtr pkt, bool fromCpuSide);

    /**
     * Perform any necessary updates to the block and perform any data
     * exchange between the packet and the block. The flags of the
     * packet are also set accordingly.
     *
     * @param pkt Request packet from upstream that hit a block
     * @param blk Cache block that the packet hit
     * @param deferred_response Whether this hit is to block that
     *                          originally missed
     * @param pending_downgrade Whether the writable flag is to be removed
     *
     * @return True if the block is to be invalidated
     */
    void satisfyRequest(PacketPtr pkt, CacheBlk *blk,
                        bool deferred_response = false,
                        bool pending_downgrade = false);

    void doTimingSupplyResponse(PacketPtr req_pkt, const uint8_t *blk_data,
                                bool already_copied, bool pending_inval);

    /**
     * Perform an upward snoop if needed, and update the block state
     * (possibly invalidating the block). Also create a response if required.
     *
     * @param pkt Snoop packet
     * @param blk Cache block being snooped
     * @param is_timing Timing or atomic for the response
     * @param is_deferred Is this a deferred snoop or not?
     * @param pending_inval Do we have a pending invalidation?
     *
     * @return The snoop delay incurred by the upwards snoop
     */
    uint32_t handleSnoop(PacketPtr pkt, CacheBlk *blk,
                         bool is_timing, bool is_deferred, bool pending_inval);

    /**
     * Create a writeback request for the given block.
     * @param blk The block to writeback.
     * @return The writeback request for the block.
     */
    PacketPtr writebackBlk(CacheBlk *blk);

    /**
     * Create a CleanEvict request for the given block.
     * @param blk The block to evict.
     * @return The CleanEvict request for the block.
     */
    PacketPtr cleanEvictBlk(CacheBlk *blk);


    void memWriteback() override;
    void memInvalidate() override;
    bool isDirty() const override;

    /**
     * Cache block visitor that writes back dirty cache blocks using
     * functional writes.
     *
     * \return Always returns true.
     */
    bool writebackVisitor(CacheBlk &blk);
    /**
     * Cache block visitor that invalidates all blocks in the cache.
     *
     * @warn Dirty cache lines will not be written back to memory.
     *
     * \return Always returns true.
     */
    bool invalidateVisitor(CacheBlk &blk);

    /**
     * Create an appropriate downstream bus request packet for the
     * given parameters.
     * @param cpu_pkt  The miss that needs to be satisfied.
     * @param blk The block currently in the cache corresponding to
     * cpu_pkt (nullptr if none).
     * @param needsWritable Indicates that the block must be writable
     * even if the request in cpu_pkt doesn't indicate that.
     * @return A new Packet containing the request, or nullptr if the
     * current request in cpu_pkt should just be forwarded on.
     */
    PacketPtr createMissPacket(PacketPtr cpu_pkt, CacheBlk *blk,
                               bool needsWritable) const;

    /**
     * Return the next queue entry to service, either a pending miss
     * from the MSHR queue, a buffered write from the write buffer, or
     * something from the prefetcher. This function is responsible
     * for prioritizing among those sources on the fly.
     */
    QueueEntry* getNextQueueEntry();

    /**
     * Send up a snoop request and find cached copies. If cached copies are
     * found, set the BLOCK_CACHED flag in pkt.
     */
    bool isCachedAbove(PacketPtr pkt, bool is_timing = true) const;

    /**
     * Return whether there are any outstanding misses.
     */
    bool outstandingMisses() const
    {
        return !mshrQueue.isEmpty();
    }

    CacheBlk *findBlock(Addr addr, bool is_secure) const {
        return tags->findBlock(addr, is_secure);
    }

    bool inCache(Addr addr, bool is_secure) const override {
        return (tags->findBlock(addr, is_secure) != 0);
    }

    bool inMissQueue(Addr addr, bool is_secure) const override {
        return (mshrQueue.findMatch(addr, is_secure) != 0);
    }

    /**
     * Find next request ready time from among possible sources.
     */
    Tick nextQueueReadyTime() const;

  public:
    /** Instantiates a basic cache object. */
    Cache(const CacheParams *p);

    /** Non-default destructor is needed to deallocate memory. */
    virtual ~Cache();

    void regStats() override;

    /**
     * Take an MSHR, turn it into a suitable downstream packet, and
     * send it out. This construct allows a queue entry to choose a suitable
     * approach based on its type.
     *
     * @param mshr The MSHR to turn into a packet and send
     * @return True if the port is waiting for a retry
     */
    bool sendMSHRQueuePacket(MSHR* mshr);

    /**
     * Similar to sendMSHR, but for a write-queue entry
     * instead. Create the packet, and send it, and if successful also
     * mark the entry in service.
     *
     * @param wq_entry The write-queue entry to turn into a packet and send
     * @return True if the port is waiting for a retry
     */
    bool sendWriteQueuePacket(WriteQueueEntry* wq_entry);

    /** serialize the state of the caches
     * We currently don't support checkpointing cache state, so this panics.
     */
    void serialize(CheckpointOut &cp) const override;
    void unserialize(CheckpointIn &cp) override;
};

/**
 * Wrap a method and present it as a cache block visitor.
 *
 * For example the forEachBlk method in the tag arrays expects a
 * callable object/function as their parameter. This class wraps a
 * method in an object and presents  callable object that adheres to
 * the cache block visitor protocol.
 */
class CacheBlkVisitorWrapper : public CacheBlkVisitor
{
  public:
    typedef bool (Cache::*VisitorPtr)(CacheBlk &blk);

    CacheBlkVisitorWrapper(Cache &_cache, VisitorPtr _visitor)
        : cache(_cache), visitor(_visitor) {}

    bool operator()(CacheBlk &blk) override {
        return (cache.*visitor)(blk);
    }

  private:
    Cache &cache;
    VisitorPtr visitor;
};

/**
 * Cache block visitor that determines if there are dirty blocks in a
 * cache.
 *
 * Use with the forEachBlk method in the tag array to determine if the
 * array contains dirty blocks.
 */
class CacheBlkIsDirtyVisitor : public CacheBlkVisitor
{
  public:
    CacheBlkIsDirtyVisitor()
        : _isDirty(false) {}

    bool operator()(CacheBlk &blk) override {
        if (blk.isDirty()) {
            _isDirty = true;
            return false;
        } else {
            return true;
        }
    }

    /**
     * Does the array contain a dirty line?
     *
     * \return true if yes, false otherwise.
     */
    bool isDirty() const { return _isDirty; };

  private:
    bool _isDirty;
};

#endif // __MEM_CACHE_CACHE_HH__