ruby: add a prefetcher

This patch adds a prefetcher for the ruby memory system. The prefetcher
is based on a prefetcher implemented by others (well, I don't know
who wrote the original). The prefetcher does stride-based prefetching,
both unit and non-unit. It obseves the misses in the cache and trains on
these. After the training period is over, the prefetcher starts issuing
prefetch requests to the controller.

1 files changed, 210 insertions, 0 deletions

diff --git a/src/mem/ruby/structures/Prefetcher.hh b/src/mem/ruby/structures/Prefetcher.hh
new file mode 100644
index 000000000..f64d39f8a
--- /dev/null
+++ b/src/mem/ruby/structures/Prefetcher.hh
@@ -0,0 +1,210 @@
+/*
+ * Copyright (c) 1999-2012 Mark D. Hill and David A. Wood
+ * 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.
+ */
+
+#ifndef PREFETCHER_H
+#define PREFETCHER_H
+
+// Implements Power 4 like prefetching
+
+#include <bitset>
+
+#include "base/statistics.hh"
+#include "mem/ruby/buffers/MessageBuffer.hh"
+#include "mem/ruby/common/Address.hh"
+#include "mem/ruby/common/Global.hh"
+#include "mem/ruby/slicc_interface/AbstractController.hh"
+#include "mem/ruby/slicc_interface/RubyRequest.hh"
+#include "params/Prefetcher.hh"
+#include "sim/sim_object.hh"
+
+#define MAX_PF_INFLIGHT 8
+
+class PrefetchEntry
+{
+    public:
+        /// constructor
+        PrefetchEntry()
+        {
+            // default: 1 cache-line stride
+            m_stride   = (1 << RubySystem::getBlockSizeBits());
+            m_use_time = Cycles(0);
+            m_is_valid = false;
+        }
+
+        //! The base address for the stream prefetch
+        Address m_address;
+
+        //! stride distance to get next address from
+        int m_stride;
+
+        //! the last time that any prefetched request was used
+        Cycles m_use_time;
+
+        //! valid bit for each stream
+        bool m_is_valid;
+
+        //! L1D prefetches loads and stores
+        RubyRequestType m_type;
+
+        //! Bitset for tracking prefetches for which addresses have been
+        //! issued, which ones have completed.
+        std::bitset<MAX_PF_INFLIGHT> requestIssued;
+        std::bitset<MAX_PF_INFLIGHT> requestCompleted;
+};
+
+class Prefetcher : public SimObject
+{
+    public:
+        typedef PrefetcherParams Params;
+        Prefetcher(const Params *p);
+        ~Prefetcher();
+
+        void issueNextPrefetch(const Address &address, PrefetchEntry *stream);
+        /**
+         * Implement the prefetch hit(miss) callback interface.
+         * These functions are called by the cache when it hits(misses)
+         * on a line with the line's prefetch bit set. If this address
+         * hits in m_array we will continue prefetching the stream.
+         */
+        void observePfHit(const Address& address);
+        void observePfMiss(const Address& address);
+
+        /**
+         * Observe a memory miss from the cache.
+         *
+         * @param address   The physical address that missed out of the cache.
+         */
+        void observeMiss(const Address& address, const RubyRequestType& type);
+
+        /**
+         * Print out some statistics
+         */
+        void print(std::ostream& out) const;
+        void setController(AbstractController *_ctrl)
+        { m_controller = _ctrl; }
+
+        void regStats();
+
+    private:
+        /**
+         * Returns an unused stream buffer (or if all are used, returns the
+         * least recently used (accessed) stream buffer).
+         * @return  The index of the least recently used stream buffer.
+         */
+        uint32_t getLRUindex(void);
+
+        //! clear a non-unit stride prefetcher entry
+        void clearNonunitEntry(uint32_t index);
+
+        //! allocate a new stream buffer at a specific index
+        void initializeStream(const Address& address, int stride,
+            uint32_t index, const RubyRequestType& type);
+
+        //! get pointer to the matching stream entry, returns NULL if not found
+        //! index holds the multiple of the stride this address is.
+        PrefetchEntry* getPrefetchEntry(const Address &address,
+            uint32_t &index);
+
+        /// access a unit stride filter to determine if there is a hit
+        bool accessUnitFilter(std::vector<Address>& filter_table,
+            uint32_t *hit_table, uint32_t &index, const Address &address,
+            int stride, bool &alloc);
+
+        /// access a unit stride filter to determine if there is a hit
+        bool accessNonunitFilter(const Address& address, int *stride,
+            bool &alloc);
+
+        //! number of prefetch streams available
+        uint32_t m_num_streams;
+        //! an array of the active prefetch streams
+        std::vector<PrefetchEntry> m_array;
+
+        //! number of misses I must see before allocating a stream
+        uint32_t m_train_misses;
+        //! number of initial prefetches to startup a stream
+        uint32_t m_num_startup_pfs;
+        //! number of stride filters
+        uint32_t m_num_unit_filters;
+        //! number of non-stride filters
+        uint32_t m_num_nonunit_filters;
+
+        /// a unit stride filter array: helps reduce BW requirement of
+        /// prefetching
+        std::vector<Address> m_unit_filter;
+        /// a round robin pointer into the unit filter group
+        uint32_t m_unit_filter_index;
+        //! An array used to count the of times particular filter entries
+        //! have been hit
+        uint32_t *m_unit_filter_hit;
+
+        //! a negative nit stride filter array: helps reduce BW requirement
+        //! of prefetching
+        std::vector<Address> m_negative_filter;
+        /// a round robin pointer into the negative filter group
+        uint32_t m_negative_filter_index;
+        /// An array used to count the of times particular filter entries
+        /// have been hit
+        uint32_t *m_negative_filter_hit;
+
+        /// a non-unit stride filter array: helps reduce BW requirement of
+        /// prefetching
+        std::vector<Address> m_nonunit_filter;
+        /// An array of strides (in # of cache lines) for the filter entries
+        int *m_nonunit_stride;
+        /// An array used to count the of times particular filter entries
+        /// have been hit
+        uint32_t *m_nonunit_hit;
+        /// a round robin pointer into the unit filter group
+        uint32_t m_nonunit_index;
+
+        /// Used for allowing prefetches across pages.
+        bool m_prefetch_cross_pages;
+
+        AbstractController *m_controller;
+
+        //! Count of accesses to the prefetcher
+        Stats::Scalar numMissObserved;
+        //! Count of prefetch streams allocated
+        Stats::Scalar numAllocatedStreams;
+        //! Count of prefetch requests made
+        Stats::Scalar numPrefetchRequested;
+        //! Count of prefetch requests accepted
+        Stats::Scalar numPrefetchAccepted;
+        //! Count of prefetches dropped
+        Stats::Scalar numDroppedPrefetches;
+        //! Count of successful prefetches
+        Stats::Scalar numHits;
+        //! Count of partial successful prefetches
+        Stats::Scalar numPartialHits;
+        //! Count of pages crossed
+        Stats::Scalar numPagesCrossed;
+        //! Count of misses incurred for blocks that were prefetched
+        Stats::Scalar numMissedPrefetchedBlocks;
+};
+
+#endif // PREFETCHER_H