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.

1 files changed, 97 insertions, 0 deletions

diff --git a/src/mem/cache/write_queue.hh b/src/mem/cache/write_queue.hh
new file mode 100644
index 000000000..006d70556
--- /dev/null
+++ b/src/mem/cache/write_queue.hh
@@ -0,0 +1,97 @@
+/*
+ * Copyright (c) 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.
+ *
+ * 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: Andreas Hansson
+ */
+
+/**
+ * @file Declaration of a queue structure to manage uncacheable write
+ * and writebacks.
+ */
+
+#ifndef __MEM_CACHE_WRITE_QUEUE_HH__
+#define __MEM_CACHE_WRITE_QUEUE_HH__
+
+#include <vector>
+
+#include "mem/cache/queue.hh"
+#include "mem/cache/write_queue_entry.hh"
+
+/**
+ * A write queue for all eviction packets, i.e. writebacks and clean
+ * evictions, as well as uncacheable writes.
+ */
+class WriteQueue : public Queue<WriteQueueEntry>
+{
+
+  public:
+
+    /**
+     * Create a write queue with a given number of entries.
+     * @param num_entries The number of entries in this queue.
+     * @param reserve The maximum number of entries needed to satisfy
+     *        any access.
+     */
+    WriteQueue(const std::string &_label, int num_entries, int reserve);
+
+    /**
+     * Allocates a new WriteQueueEntry for the request and size. This
+     * places the request as the first target in the WriteQueueEntry.
+     *
+     * @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 is the WriteQueueEntry be ready to act upon.
+     * @param order The logical order of this WriteQueueEntry
+     *
+     * @return The a pointer to the WriteQueueEntry allocated.
+     *
+     * @pre There are free entries.
+     */
+    WriteQueueEntry *allocate(Addr blk_addr, unsigned blk_size,
+                              PacketPtr pkt, Tick when_ready, Counter order);
+
+    /**
+     * Mark the given entry as in service. This removes the entry from
+     * the readyList or deallocates the entry if it does not expect a
+     * response (writeback/eviction rather than an uncacheable write).
+     *
+     * @param entry The entry to mark in service.
+     */
+    void markInService(WriteQueueEntry *entry);
+};
+
+#endif //__MEM_CACHE_WRITE_QUEUE_HH__