summaryrefslogtreecommitdiff
path: root/src/mem/ruby/structures/Prefetcher.hh
diff options
context:
space:
mode:
authorNilay Vaish <nilay@cs.wisc.edu>2012-12-11 10:05:54 -0600
committerNilay Vaish <nilay@cs.wisc.edu>2012-12-11 10:05:54 -0600
commit93e283abb348b81d086225f7861d94901c9b0888 (patch)
tree2f66e364c898392ac5538d1cb9726720c34eecfd /src/mem/ruby/structures/Prefetcher.hh
parentd5023847951dcebcb38838cae0a141bd1a62e407 (diff)
downloadgem5-93e283abb348b81d086225f7861d94901c9b0888.tar.xz
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.
Diffstat (limited to 'src/mem/ruby/structures/Prefetcher.hh')
-rw-r--r--src/mem/ruby/structures/Prefetcher.hh210
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