b496d4abce
Reference:
Xiangyao Yu, Christopher J. Hughes, Nadathur Satish, and Srinivas Devadas.
2015. IMP: indirect memory prefetcher. In Proceedings of the 48th
International Symposium on Microarchitecture (MICRO-48). ACM,
New York, NY, USA, 178-190. DOI: https://doi.org/10.1145/2830772.2830807
Change-Id: I52790f69c13ec55b8c1c8b9396ef9a1fb1be9797
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/16223
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
270 lines
11 KiB
C++
270 lines
11 KiB
C++
/**
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* Copyright (c) 2018 Metempsy Technology Consulting
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are
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* met: redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer;
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* redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution;
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* neither the name of the copyright holders nor the names of its
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* contributors may be used to endorse or promote products derived from
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* this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* Authors: Javier Bueno
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*/
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#include "mem/cache/prefetch/indirect_memory.hh"
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#include "mem/cache/base.hh"
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#include "mem/cache/prefetch/associative_set_impl.hh"
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#include "params/IndirectMemoryPrefetcher.hh"
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IndirectMemoryPrefetcher::IndirectMemoryPrefetcher(
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const IndirectMemoryPrefetcherParams *p) : QueuedPrefetcher(p),
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maxPrefetchDistance(p->max_prefetch_distance),
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shiftValues(p->shift_values), prefetchThreshold(p->prefetch_threshold),
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maxIndirectCounterValue(p->max_indirect_counter_value),
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streamCounterThreshold(p->stream_counter_threshold),
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streamingDistance(p->streaming_distance),
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prefetchTable(p->pt_table_assoc, p->pt_table_entries,
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p->pt_table_indexing_policy, p->pt_table_replacement_policy),
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ipd(p->ipd_table_assoc, p->ipd_table_entries, p->ipd_table_indexing_policy,
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p->ipd_table_replacement_policy,
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IndirectPatternDetectorEntry(p->addr_array_len, shiftValues.size())),
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ipdEntryTrackingMisses(nullptr),
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#if THE_ISA != NULL_ISA
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byteOrder(TheISA::GuestByteOrder)
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#else
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byteOrder((ByteOrder) -1)
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#endif
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{
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fatal_if(byteOrder == -1, "This prefetcher requires a defined ISA\n");
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}
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void
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IndirectMemoryPrefetcher::calculatePrefetch(const PrefetchInfo &pfi,
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std::vector<AddrPriority> &addresses)
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{
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// This prefetcher requires a PC
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if (!pfi.hasPC()) {
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return;
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}
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bool is_secure = pfi.isSecure();
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Addr pc = pfi.getPC();
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Addr addr = pfi.getAddr();
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bool miss = pfi.isCacheMiss();
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checkAccessMatchOnActiveEntries(addr);
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// First check if this is a miss, if the prefetcher is tracking misses
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if (ipdEntryTrackingMisses != nullptr && miss) {
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// Check if the entry tracking misses has already set its second index
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if (!ipdEntryTrackingMisses->secondIndexSet) {
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trackMissIndex1(addr);
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} else {
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trackMissIndex2(addr);
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}
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} else {
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// if misses are not being tracked, attempt to detect stream accesses
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PrefetchTableEntry *pt_entry =
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prefetchTable.findEntry(pc, false /* unused */);
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if (pt_entry != nullptr) {
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prefetchTable.accessEntry(pt_entry);
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if (pt_entry->address != addr) {
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// Streaming access found
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pt_entry->streamCounter += 1;
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if (pt_entry->streamCounter >= streamCounterThreshold) {
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int64_t delta = addr - pt_entry->address;
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for (unsigned int i = 1; i <= streamingDistance; i += 1) {
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addresses.push_back(AddrPriority(addr + delta * i, 0));
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}
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}
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pt_entry->address = addr;
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pt_entry->secure = is_secure;
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// if this is a read, read the data from the cache and assume
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// it is an index (this is only possible if the data is already
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// in the cache), also, only indexes up to 8 bytes are
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// considered
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if (!miss && !pfi.isWrite() && pfi.getSize() <= 8) {
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int64_t index = 0;
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switch(pfi.getSize()) {
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case sizeof(uint8_t):
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index = pfi.get<uint8_t>(byteOrder);
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break;
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case sizeof(uint16_t):
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index = pfi.get<uint16_t>(byteOrder);
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break;
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case sizeof(uint32_t):
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index = pfi.get<uint32_t>(byteOrder);
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break;
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case sizeof(uint64_t):
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index = pfi.get<uint64_t>(byteOrder);
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break;
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default:
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panic("Invalid access size\n");
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}
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if (!pt_entry->enabled) {
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// Not enabled (no pattern detected in this stream),
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// add or update an entry in the pattern detector and
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// start tracking misses
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allocateOrUpdateIPDEntry(pt_entry, index);
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} else {
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// Enabled entry, update the index
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pt_entry->index = index;
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if (!pt_entry->increasedIndirectCounter) {
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if (pt_entry->indirectCounter > 0) {
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pt_entry->indirectCounter -= 1;
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}
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} else {
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// Set this to false, to see if the new index
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// has any match
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pt_entry->increasedIndirectCounter = false;
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}
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// If the counter is high enough, start prefetching
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if (pt_entry->indirectCounter > prefetchThreshold) {
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unsigned distance = pt_entry->indirectCounter *
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maxPrefetchDistance / maxIndirectCounterValue;
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for (int delta = 1; delta < distance; delta += 1) {
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Addr pf_addr = pt_entry->baseAddr +
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(pt_entry->index << pt_entry->shift);
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addresses.push_back(AddrPriority(pf_addr, 0));
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}
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}
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}
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}
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}
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} else {
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pt_entry = prefetchTable.findVictim(pc);
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assert(pt_entry != nullptr);
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prefetchTable.insertEntry(pc, false /* unused */, pt_entry);
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pt_entry->address = addr;
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pt_entry->secure = is_secure;
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}
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}
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}
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void
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IndirectMemoryPrefetcher::allocateOrUpdateIPDEntry(
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const PrefetchTableEntry *pt_entry, int64_t index)
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{
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// The address of the pt_entry is used to index the IPD
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Addr ipd_entry_addr = (Addr) pt_entry;
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IndirectPatternDetectorEntry *ipd_entry = ipd.findEntry(ipd_entry_addr,
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false/* unused */);
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if (ipd_entry != nullptr) {
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ipd.accessEntry(ipd_entry);
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if (!ipd_entry->secondIndexSet) {
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// Second time we see an index, fill idx2
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ipd_entry->idx2 = index;
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ipd_entry->secondIndexSet = true;
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ipdEntryTrackingMisses = ipd_entry;
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} else {
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// Third access! no pattern has been found so far,
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// release the IPD entry
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ipd_entry->reset();
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ipdEntryTrackingMisses = nullptr;
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}
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} else {
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ipd_entry = ipd.findVictim(ipd_entry_addr);
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assert(ipd_entry != nullptr);
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ipd.insertEntry(ipd_entry_addr, false /* unused */, ipd_entry);
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ipd_entry->idx1 = index;
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ipdEntryTrackingMisses = ipd_entry;
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}
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}
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void
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IndirectMemoryPrefetcher::trackMissIndex1(Addr miss_addr)
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{
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IndirectPatternDetectorEntry *entry = ipdEntryTrackingMisses;
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// If the second index is not set, we are just filling the baseAddr
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// vector
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assert(entry->numMisses < entry->baseAddr.size());
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std::vector<Addr> &ba_array = entry->baseAddr[entry->numMisses];
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int idx = 0;
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for (int shift : shiftValues) {
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ba_array[idx] = miss_addr - (entry->idx1 << shift);
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idx += 1;
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}
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entry->numMisses += 1;
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if (entry->numMisses == entry->baseAddr.size()) {
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// stop tracking misses once we have tracked enough
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ipdEntryTrackingMisses = nullptr;
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}
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}
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void
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IndirectMemoryPrefetcher::trackMissIndex2(Addr miss_addr)
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{
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IndirectPatternDetectorEntry *entry = ipdEntryTrackingMisses;
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// Second index is filled, compare the addresses generated during
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// the previous misses (using idx1) against newly generated values
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// using idx2, if a match is found, fill the additional fields
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// of the PT entry
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for (int midx = 0; midx < entry->numMisses; midx += 1)
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{
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std::vector<Addr> &ba_array = entry->baseAddr[midx];
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int idx = 0;
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for (int shift : shiftValues) {
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if (ba_array[idx] == (miss_addr - (entry->idx2 << shift))) {
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// Match found!
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// Fill the corresponding pt_entry
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PrefetchTableEntry *pt_entry =
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(PrefetchTableEntry *) entry->getTag();
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pt_entry->baseAddr = ba_array[idx];
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pt_entry->shift = shift;
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pt_entry->enabled = true;
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pt_entry->indirectCounter = 0;
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// Release the current IPD Entry
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entry->reset();
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// Do not track more misses
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ipdEntryTrackingMisses = nullptr;
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return;
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}
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idx += 1;
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}
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}
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}
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void
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IndirectMemoryPrefetcher::checkAccessMatchOnActiveEntries(Addr addr)
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{
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for (auto &pt_entry : prefetchTable) {
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if (pt_entry.enabled) {
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if (addr == pt_entry.baseAddr +
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(pt_entry.index << pt_entry.shift)) {
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if (pt_entry.indirectCounter < maxIndirectCounterValue) {
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pt_entry.indirectCounter += 1;
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pt_entry.increasedIndirectCounter = true;
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}
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}
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}
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}
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}
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IndirectMemoryPrefetcher*
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IndirectMemoryPrefetcherParams::create()
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{
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return new IndirectMemoryPrefetcher(this);
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}
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