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/**
* Copyright (c) 2018 Metempsy Technology Consulting
* 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: Javier Bueno
*/
#include "mem/cache/prefetch/indirect_memory.hh"
#include "mem/cache/base.hh"
#include "mem/cache/prefetch/associative_set_impl.hh"
#include "params/IndirectMemoryPrefetcher.hh"
IndirectMemoryPrefetcher::IndirectMemoryPrefetcher(
const IndirectMemoryPrefetcherParams *p) : QueuedPrefetcher(p),
maxPrefetchDistance(p->max_prefetch_distance),
shiftValues(p->shift_values), prefetchThreshold(p->prefetch_threshold),
maxIndirectCounterValue(p->max_indirect_counter_value),
streamCounterThreshold(p->stream_counter_threshold),
streamingDistance(p->streaming_distance),
prefetchTable(p->pt_table_assoc, p->pt_table_entries,
p->pt_table_indexing_policy, p->pt_table_replacement_policy),
ipd(p->ipd_table_assoc, p->ipd_table_entries, p->ipd_table_indexing_policy,
p->ipd_table_replacement_policy,
IndirectPatternDetectorEntry(p->addr_array_len, shiftValues.size())),
ipdEntryTrackingMisses(nullptr),
#if THE_ISA != NULL_ISA
byteOrder(TheISA::GuestByteOrder)
#else
byteOrder((ByteOrder) -1)
#endif
{
fatal_if(byteOrder == static_cast<ByteOrder>(-1),
"This prefetcher requires a defined ISA\n");
}
void
IndirectMemoryPrefetcher::calculatePrefetch(const PrefetchInfo &pfi,
std::vector<AddrPriority> &addresses)
{
// This prefetcher requires a PC
if (!pfi.hasPC()) {
return;
}
bool is_secure = pfi.isSecure();
Addr pc = pfi.getPC();
Addr addr = pfi.getAddr();
bool miss = pfi.isCacheMiss();
checkAccessMatchOnActiveEntries(addr);
// First check if this is a miss, if the prefetcher is tracking misses
if (ipdEntryTrackingMisses != nullptr && miss) {
// Check if the entry tracking misses has already set its second index
if (!ipdEntryTrackingMisses->secondIndexSet) {
trackMissIndex1(addr);
} else {
trackMissIndex2(addr);
}
} else {
// if misses are not being tracked, attempt to detect stream accesses
PrefetchTableEntry *pt_entry =
prefetchTable.findEntry(pc, false /* unused */);
if (pt_entry != nullptr) {
prefetchTable.accessEntry(pt_entry);
if (pt_entry->address != addr) {
// Streaming access found
pt_entry->streamCounter += 1;
if (pt_entry->streamCounter >= streamCounterThreshold) {
int64_t delta = addr - pt_entry->address;
for (unsigned int i = 1; i <= streamingDistance; i += 1) {
addresses.push_back(AddrPriority(addr + delta * i, 0));
}
}
pt_entry->address = addr;
pt_entry->secure = is_secure;
// if this is a read, read the data from the cache and assume
// it is an index (this is only possible if the data is already
// in the cache), also, only indexes up to 8 bytes are
// considered
if (!miss && !pfi.isWrite() && pfi.getSize() <= 8) {
int64_t index = 0;
bool read_index = true;
switch(pfi.getSize()) {
case sizeof(uint8_t):
index = pfi.get<uint8_t>(byteOrder);
break;
case sizeof(uint16_t):
index = pfi.get<uint16_t>(byteOrder);
break;
case sizeof(uint32_t):
index = pfi.get<uint32_t>(byteOrder);
break;
case sizeof(uint64_t):
index = pfi.get<uint64_t>(byteOrder);
break;
default:
// Ignore non-power-of-two sizes
read_index = false;
}
if (read_index && !pt_entry->enabled) {
// Not enabled (no pattern detected in this stream),
// add or update an entry in the pattern detector and
// start tracking misses
allocateOrUpdateIPDEntry(pt_entry, index);
} else if (read_index) {
// Enabled entry, update the index
pt_entry->index = index;
if (!pt_entry->increasedIndirectCounter) {
if (pt_entry->indirectCounter > 0) {
pt_entry->indirectCounter -= 1;
}
} else {
// Set this to false, to see if the new index
// has any match
pt_entry->increasedIndirectCounter = false;
}
// If the counter is high enough, start prefetching
if (pt_entry->indirectCounter > prefetchThreshold) {
unsigned distance = pt_entry->indirectCounter *
maxPrefetchDistance / maxIndirectCounterValue;
for (int delta = 1; delta < distance; delta += 1) {
Addr pf_addr = pt_entry->baseAddr +
(pt_entry->index << pt_entry->shift);
addresses.push_back(AddrPriority(pf_addr, 0));
}
}
}
}
}
} else {
pt_entry = prefetchTable.findVictim(pc);
assert(pt_entry != nullptr);
prefetchTable.insertEntry(pc, false /* unused */, pt_entry);
pt_entry->address = addr;
pt_entry->secure = is_secure;
}
}
}
void
IndirectMemoryPrefetcher::allocateOrUpdateIPDEntry(
const PrefetchTableEntry *pt_entry, int64_t index)
{
// The address of the pt_entry is used to index the IPD
Addr ipd_entry_addr = (Addr) pt_entry;
IndirectPatternDetectorEntry *ipd_entry = ipd.findEntry(ipd_entry_addr,
false/* unused */);
if (ipd_entry != nullptr) {
ipd.accessEntry(ipd_entry);
if (!ipd_entry->secondIndexSet) {
// Second time we see an index, fill idx2
ipd_entry->idx2 = index;
ipd_entry->secondIndexSet = true;
ipdEntryTrackingMisses = ipd_entry;
} else {
// Third access! no pattern has been found so far,
// release the IPD entry
ipd_entry->reset();
ipdEntryTrackingMisses = nullptr;
}
} else {
ipd_entry = ipd.findVictim(ipd_entry_addr);
assert(ipd_entry != nullptr);
ipd.insertEntry(ipd_entry_addr, false /* unused */, ipd_entry);
ipd_entry->idx1 = index;
ipdEntryTrackingMisses = ipd_entry;
}
}
void
IndirectMemoryPrefetcher::trackMissIndex1(Addr miss_addr)
{
IndirectPatternDetectorEntry *entry = ipdEntryTrackingMisses;
// If the second index is not set, we are just filling the baseAddr
// vector
assert(entry->numMisses < entry->baseAddr.size());
std::vector<Addr> &ba_array = entry->baseAddr[entry->numMisses];
int idx = 0;
for (int shift : shiftValues) {
ba_array[idx] = miss_addr - (entry->idx1 << shift);
idx += 1;
}
entry->numMisses += 1;
if (entry->numMisses == entry->baseAddr.size()) {
// stop tracking misses once we have tracked enough
ipdEntryTrackingMisses = nullptr;
}
}
void
IndirectMemoryPrefetcher::trackMissIndex2(Addr miss_addr)
{
IndirectPatternDetectorEntry *entry = ipdEntryTrackingMisses;
// Second index is filled, compare the addresses generated during
// the previous misses (using idx1) against newly generated values
// using idx2, if a match is found, fill the additional fields
// of the PT entry
for (int midx = 0; midx < entry->numMisses; midx += 1)
{
std::vector<Addr> &ba_array = entry->baseAddr[midx];
int idx = 0;
for (int shift : shiftValues) {
if (ba_array[idx] == (miss_addr - (entry->idx2 << shift))) {
// Match found!
// Fill the corresponding pt_entry
PrefetchTableEntry *pt_entry =
(PrefetchTableEntry *) entry->getTag();
pt_entry->baseAddr = ba_array[idx];
pt_entry->shift = shift;
pt_entry->enabled = true;
pt_entry->indirectCounter = 0;
// Release the current IPD Entry
entry->reset();
// Do not track more misses
ipdEntryTrackingMisses = nullptr;
return;
}
idx += 1;
}
}
}
void
IndirectMemoryPrefetcher::checkAccessMatchOnActiveEntries(Addr addr)
{
for (auto &pt_entry : prefetchTable) {
if (pt_entry.enabled) {
if (addr == pt_entry.baseAddr +
(pt_entry.index << pt_entry.shift)) {
if (pt_entry.indirectCounter < maxIndirectCounterValue) {
pt_entry.indirectCounter += 1;
pt_entry.increasedIndirectCounter = true;
}
}
}
}
}
IndirectMemoryPrefetcher*
IndirectMemoryPrefetcherParams::create()
{
return new IndirectMemoryPrefetcher(this);
}