gem5/src/mem/cache/cache.hh

/*
 * Copyright (c) 2012-2018 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
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 */

/**
 * @file
 * Describes a cache
 */

#ifndef __MEM_CACHE_CACHE_HH__
#define __MEM_CACHE_CACHE_HH__

#include <cstdint>
#include <unordered_set>

#include "base/compiler.hh"
#include "base/types.hh"
#include "mem/cache/base.hh"
#include "mem/packet.hh"

namespace gem5
{

class CacheBlk;
struct CacheParams;
class MSHR;

/**
 * A coherent cache that can be arranged in flexible topologies.
 */
class Cache : public BaseCache
{
  protected:
    /**
     * This cache should allocate a block on a line-sized write miss.
     */
    const bool doFastWrites;

    /**
     * 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;

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

    bool access(PacketPtr pkt, CacheBlk *&blk, Cycles &lat,
                PacketList &writebacks) override;

    void handleTimingReqHit(PacketPtr pkt, CacheBlk *blk,
                            Tick request_time) override;

    void handleTimingReqMiss(PacketPtr pkt, CacheBlk *blk,
                             Tick forward_time,
                             Tick request_time) override;

    void recvTimingReq(PacketPtr pkt) override;

    void doWritebacks(PacketList& writebacks, Tick forward_time) override;

    void doWritebacksAtomic(PacketList& writebacks) override;

    void serviceMSHRTargets(MSHR *mshr, const PacketPtr pkt,
                            CacheBlk *blk) override;

    void recvTimingSnoopReq(PacketPtr pkt) override;

    void recvTimingSnoopResp(PacketPtr pkt) override;

    Cycles handleAtomicReqMiss(PacketPtr pkt, CacheBlk *&blk,
                               PacketList &writebacks) override;

    Tick recvAtomic(PacketPtr pkt) override;

    Tick recvAtomicSnoop(PacketPtr pkt) override;

    void satisfyRequest(PacketPtr pkt, CacheBlk *blk,
                        bool deferred_response = false,
                        bool pending_downgrade = false) override;

    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);

    [[nodiscard]] PacketPtr evictBlock(CacheBlk *blk) override;

    /**
     * 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);

    PacketPtr createMissPacket(PacketPtr cpu_pkt, CacheBlk *blk,
                               bool needs_writable,
                               bool is_whole_line_write) const override;

    /**
     * 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);

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

    /**
     * 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) override;
};

} // namespace gem5

#endif // __MEM_CACHE_CACHE_HH__