mem: Create a separate class for the cache write buffer

This patch breaks out the cache write buffer into a separate class,
without affecting any stats. The goal of the patch is to avoid
encumbering the much-simpler write queue with the complex MSHR
handling. In a follow on patch this simplification allows us to
implement write combining.

The WriteQueue gets its own class, but shares a common ancestor, the
generic Queue, with the MSHRQueue.

src/mem/cache/write_queue_entry.hh

@@ -0,0 +1,194 @@
+/*
+ * Copyright (c) 2012-2013, 2015-2016 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
+ *          Andreas Hansson
+ */
+
+/**
+ * @file
+ * Write queue entry
+ */
+
+#ifndef __MEM_CACHE_WRITE_QUEUE_ENTRY_HH__
+#define __MEM_CACHE_WRITE_QUEUE_ENTRY_HH__
+
+#include <list>
+
+#include "base/printable.hh"
+#include "mem/cache/queue_entry.hh"
+
+class Cache;
+
+/**
+ * Write queue entry
+ */
+class WriteQueueEntry : public QueueEntry, public Printable
+{
+
+    /**
+     * Consider the queues friends to avoid making everything public.
+     */
+    template<typename Entry>
+    friend class Queue;
+    friend class WriteQueue;
+
+  public:
+
+    class Target {
+      public:
+
+        const Tick recvTime;  //!< Time when request was received (for stats)
+        const Tick readyTime; //!< Time when request is ready to be serviced
+        const Counter order;  //!< Global order (for memory consistency mgmt)
+        const PacketPtr pkt;  //!< Pending request packet.
+
+        Target(PacketPtr _pkt, Tick _readyTime, Counter _order)
+            : recvTime(curTick()), readyTime(_readyTime), order(_order),
+              pkt(_pkt)
+        {}
+    };
+
+    class TargetList : public std::list<Target> {
+
+      public:
+
+        TargetList() {}
+        void add(PacketPtr pkt, Tick readyTime, Counter order);
+        bool checkFunctional(PacketPtr pkt);
+        void print(std::ostream &os, int verbosity,
+                   const std::string &prefix) const;
+    };
+
+    /** A list of write queue entriess. */
+    typedef std::list<WriteQueueEntry *> List;
+    /** WriteQueueEntry list iterator. */
+    typedef List::iterator Iterator;
+
+    bool sendPacket(Cache &cache);
+
+  private:
+
+    /**
+     * Pointer to this entry on the ready list.
+     * @sa MissQueue, WriteQueue::readyList
+     */
+    Iterator readyIter;
+
+    /**
+     * Pointer to this entry on the allocated list.
+     * @sa MissQueue, WriteQueue::allocatedList
+     */
+    Iterator allocIter;
+
+    /** List of all requests that match the address */
+    TargetList targets;
+
+  public:
+
+    /** A simple constructor. */
+    WriteQueueEntry() {}
+
+    /**
+     * Allocate a miss to this entry.
+     * @param blk_addr The address of the block.
+     * @param blk_size The number of bytes to request.
+     * @param pkt The original write.
+     * @param when_ready When should the write be sent out.
+     * @param _order The logical order of this write.
+     */
+    void allocate(Addr blk_addr, unsigned blk_size, PacketPtr pkt,
+                  Tick when_ready, Counter _order);
+
+    bool markInService();
+
+    /**
+     * Mark this entry as free.
+     */
+    void deallocate();
+
+    /**
+     * Returns the current number of allocated targets.
+     * @return The current number of allocated targets.
+     */
+    int getNumTargets() const
+    { return targets.size(); }
+
+    /**
+     * Returns true if there are targets left.
+     * @return true if there are targets
+     */
+    bool hasTargets() const { return !targets.empty(); }
+
+    /**
+     * Returns a reference to the first target.
+     * @return A pointer to the first target.
+     */
+    Target *getTarget()
+    {
+        assert(hasTargets());
+        return &targets.front();
+    }
+
+    /**
+     * Pop first target.
+     */
+    void popTarget()
+    {
+        targets.pop_front();
+    }
+
+    bool checkFunctional(PacketPtr pkt);
+
+    /**
+     * Prints the contents of this MSHR for debugging.
+     */
+    void print(std::ostream &os,
+               int verbosity = 0,
+               const std::string &prefix = "") const;
+    /**
+     * A no-args wrapper of print(std::ostream...)  meant to be
+     * invoked from DPRINTFs avoiding string overheads in fast mode
+     *
+     * @return string with mshr fields
+     */
+    std::string print() const;
+};
+
+#endif // __MEM_CACHE_WRITE_QUEUE_ENTRY_HH__