gem5/src/mem/packet_queue.hh

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 * Copyright (c) 2006 The Regents of The University of Michigan
 * All rights reserved.
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#ifndef __MEM_PACKET_QUEUE_HH__
#define __MEM_PACKET_QUEUE_HH__

/**
 * @file
 * Declaration of a simple PacketQueue that is associated with
 * a port on which it attempts to send packets according to the time
 * stamp given to them at insertion. The packet queue is responsible
 * for the flow control of the port.
 */

#include <list>

#include "mem/port.hh"
#include "sim/drain.hh"
#include "sim/eventq.hh"

namespace gem5
{

/**
 * A packet queue is a class that holds deferred packets and later
 * sends them using the associated CPU-side port or memory-side port.
 */
class PacketQueue : public Drainable
{
  private:
    /** A deferred packet, buffered to transmit later. */
    class DeferredPacket
    {
      public:
        Tick tick;      ///< The tick when the packet is ready to transmit
        PacketPtr pkt;  ///< Pointer to the packet to transmit
        DeferredPacket(Tick t, PacketPtr p)
            : tick(t), pkt(p)
        {}
    };

    typedef std::list<DeferredPacket> DeferredPacketList;

    /** A list of outgoing packets. */
    DeferredPacketList transmitList;

    /** The manager which is used for the event queue */
    EventManager& em;

    /** Used to schedule sending of deferred packets. */
    void processSendEvent();

    /** Event used to call processSendEvent. */
    EventFunctionWrapper sendEvent;

     /*
      * Optionally disable the sanity check
      * on the size of the transmitList. The
      * sanity check will be enabled by default.
      */
    bool _disableSanityCheck;

    /**
     * if true, inserted packets have to be unconditionally scheduled
     * after the last packet in the queue that references the same
     * address
     */
    bool forceOrder;

  protected:

    /** Label to use for print request packets label stack. */
    const std::string label;

    /** Remember whether we're awaiting a retry. */
    bool waitingOnRetry;

    /** Check whether we have a packet ready to go on the transmit list. */
    bool deferredPacketReady() const
    { return !transmitList.empty() && transmitList.front().tick <= curTick(); }

    /**
     * Attempt to send a packet. Note that a subclass of the
     * PacketQueue can override this method and thus change the
     * behaviour (as done by the cache for the request queue). The
     * default implementation sends the head of the transmit list. The
     * caller must guarantee that the list is non-empty and that the
     * head packet is scheduled for curTick() (or earlier).
     */
    virtual void sendDeferredPacket();

    /**
     * Send a packet using the appropriate method for the specific
     * subclass (request, response or snoop response).
     */
    virtual bool sendTiming(PacketPtr pkt) = 0;

    /**
     * Create a packet queue, linked to an event manager, and a label
     * that will be used for functional print request packets.
     *
     * @param _em Event manager used for scheduling this queue
     * @param _label Label to push on the label stack for print request packets
     * @param force_order Force insertion order for packets with same address
     * @param disable_sanity_check Flag used to disable the sanity check
     *        on the size of the transmitList. The check is enabled by default.
     */
    PacketQueue(EventManager& _em, const std::string& _label,
                const std::string& _sendEventName,
                bool force_order = false,
                bool disable_sanity_check = false);

    /**
     * Virtual desctructor since the class may be used as a base class.
     */
    virtual ~PacketQueue();

  public:

    /**
     * Provide a name to simplify debugging.
     *
     * @return A complete name, appended to module and port
     */
    virtual const std::string name() const = 0;

    /**
     * Get the size of the queue.
     */
    size_t size() const { return transmitList.size(); }

    /**
     * Get the next packet ready time.
     */
    Tick deferredPacketReadyTime() const
    { return transmitList.empty() ? MaxTick : transmitList.front().tick; }

    /**
     * Check if a packet corresponding to the same address exists in the
     * queue.
     *
     * @param pkt The packet to compare against.
     * @param blk_size Block size in bytes.
     * @return Whether a corresponding packet is found.
     */
    bool checkConflict(const PacketPtr pkt, const int blk_size) const;

    /** Check the list of buffered packets against the supplied
     * functional request. */
    bool trySatisfyFunctional(PacketPtr pkt);

    /**
     * Schedule a send event if we are not already waiting for a
     * retry. If the requested time is before an already scheduled
     * send event, the event will be rescheduled. If MaxTick is
     * passed, no event is scheduled. Instead, if we are idle and
     * asked to drain then check and signal drained.
     *
     * @param when time to schedule an event
     */
    void schedSendEvent(Tick when);

    /**
     * Add a packet to the transmit list, and schedule a send event.
     *
     * @param pkt Packet to send
     * @param when Absolute time (in ticks) to send packet
     */
    void schedSendTiming(PacketPtr pkt, Tick when);

    /**
     * Retry sending a packet from the queue. Note that this is not
     * necessarily the same packet if something has been added with an
     * earlier time stamp.
     */
    void retry();

    /**
      * This allows a user to explicitly disable the sanity check
      * on the size of the transmitList, which is enabled by default.
      * Users must use this function to explicitly disable the sanity
      * check.
      */
    void disableSanityCheck() { _disableSanityCheck = true; }

    DrainState drain() override;
};

class ReqPacketQueue : public PacketQueue
{

  protected:

    RequestPort& memSidePort;

    // Static definition so it can be called when constructing the parent
    // without us being completely initialized.
    static const std::string name(const RequestPort& memSidePort,
                                  const std::string& label)
    { return memSidePort.name() + "-" + label; }

  public:

    /**
     * Create a request packet queue, linked to an event manager, a
     * memory-side port, and a label that will be used for functional print
     * request packets.
     *
     * @param _em Event manager used for scheduling this queue
     * @param _mem_side_port Mem_side port used to send the packets
     * @param _label Label to push on the label stack for print request packets
     */
    ReqPacketQueue(EventManager& _em, RequestPort& _mem_side_port,
                   const std::string _label = "ReqPacketQueue");

    virtual ~ReqPacketQueue() { }

    const std::string name() const
    { return name(memSidePort, label); }

    bool sendTiming(PacketPtr pkt);

};

class SnoopRespPacketQueue : public PacketQueue
{

  protected:

    RequestPort& memSidePort;

    // Static definition so it can be called when constructing the parent
    // without us being completely initialized.
    static const std::string name(const RequestPort& memSidePort,
                                  const std::string& label)
    { return memSidePort.name() + "-" + label; }

  public:

    /**
     * Create a snoop response packet queue, linked to an event
     * manager, a memory-side port, and a label that will be used for
     * functional print request packets.
     *
     * @param _em Event manager used for scheduling this queue
     * @param _mem_side_port memory-side port used to send the packets
     * @param force_order Force insertion order for packets with same address
     * @param _label Label to push on the label stack for print request packets
     */
    SnoopRespPacketQueue(EventManager& _em, RequestPort& _mem_side_port,
                         bool force_order = false,
                         const std::string _label = "SnoopRespPacketQueue");

    virtual ~SnoopRespPacketQueue() { }

    const std::string name() const
    { return name(memSidePort, label); }

    bool sendTiming(PacketPtr pkt);

};

class RespPacketQueue : public PacketQueue
{

  protected:

    ResponsePort& cpuSidePort;

    // Static definition so it can be called when constructing the parent
    // without us being completely initialized.
    static const std::string name(const ResponsePort& cpuSidePort,
                                  const std::string& label)
    { return cpuSidePort.name() + "-" + label; }

  public:

    /**
     * Create a response packet queue, linked to an event manager, a
     * CPU-side port, and a label that will be used for functional print
     * request packets.
     *
     * @param _em Event manager used for scheduling this queue
     * @param _cpu_side_port Cpu_side port used to send the packets
     * @param force_order Force insertion order for packets with same address
     * @param _label Label to push on the label stack for print request packets
     */
    RespPacketQueue(EventManager& _em, ResponsePort& _cpu_side_port,
                    bool force_order = false,
                    const std::string _label = "RespPacketQueue");

    virtual ~RespPacketQueue() { }

    const std::string name() const
    { return name(cpuSidePort, label); }

    bool sendTiming(PacketPtr pkt);

};

} // namespace gem5

#endif // __MEM_PACKET_QUEUE_HH__