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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/delta_correlating_prediction_tables.hh"
#include "debug/HWPrefetch.hh"
#include "mem/cache/prefetch/associative_set_impl.hh"
#include "params/DCPTPrefetcher.hh"
#include "params/DeltaCorrelatingPredictionTables.hh"
DeltaCorrelatingPredictionTables::DeltaCorrelatingPredictionTables(
DeltaCorrelatingPredictionTablesParams *p) : SimObject(p),
deltaBits(p->delta_bits), deltaMaskBits(p->delta_mask_bits),
table(p->table_assoc, p->table_entries, p->table_indexing_policy,
p->table_replacement_policy, DCPTEntry(p->deltas_per_entry))
{
}
void
DeltaCorrelatingPredictionTables::DCPTEntry::reset()
{
for (auto &delta : deltas) {
delta = 0;
}
lastAddress = 0;
deltaPointer = 0;
}
void
DeltaCorrelatingPredictionTables::DCPTEntry::addAddress(Addr address,
unsigned int delta_bits)
{
if ((address - lastAddress) != 0) {
Addr delta = address - lastAddress;
// Account for the sign bit
Addr max_positive_delta = (1 << (delta_bits-1)) - 1;
if (address > lastAddress) {
// check positive delta overflow
if (delta > max_positive_delta) {
delta = 0;
}
} else {
// check negative delta overflow
if (lastAddress - address > (max_positive_delta + 1)) {
delta = 0;
}
}
deltas[deltaPointer] = delta;
deltaPointer = (deltaPointer + 1) % deltas.size();
lastAddress = address;
}
}
void
DeltaCorrelatingPredictionTables::DCPTEntry::getCandidates(
std::vector<QueuedPrefetcher::AddrPriority> &pfs, unsigned int mask) const
{
// most recent index
unsigned int last = (deltaPointer - 1) % deltas.size();
// second most recent index
unsigned int last_prev = (deltaPointer - 2) % deltas.size();
int delta_0 = deltas[last_prev];
int delta_1 = deltas[last];
// a delta 0 means that it overflowed, we can not match it
if (delta_0 == 0 || delta_1 == 0) {
return;
}
// Try to find the two most recent deltas in a previous position on the
// delta circular array, if found, start issuing prefetches using the
// remaining deltas (adding each delta to the last Addr to generate the
// prefetched address.
// oldest index
int idx_0 = deltaPointer + 1;
// second oldest index
int idx_1 = deltaPointer + 2;
for (int i = 0; i < deltas.size() - 2; i += 1) {
int this_delta_0 = deltas[(idx_0 + i) % deltas.size()];
int this_delta_1 = deltas[(idx_1 + i) % deltas.size()];
if ((this_delta_0 >> mask) == (delta_0 >> mask) &&
(this_delta_1 >> mask) == (delta_1 >> mask)) {
Addr addr = lastAddress;
// Pattern found, issue prefetches with the remaining deltas after
// this pair
i += 2; // skip the matching pair
do {
int pf_delta = deltas[(idx_0 + i) % deltas.size()];
addr += pf_delta;
pfs.push_back(QueuedPrefetcher::AddrPriority(addr, 0));
i += 1;
} while (i < deltas.size() - 2);
}
}
}
void
DeltaCorrelatingPredictionTables::calculatePrefetch(
const BasePrefetcher::PrefetchInfo &pfi,
std::vector<QueuedPrefetcher::AddrPriority> &addresses)
{
if (!pfi.hasPC()) {
DPRINTF(HWPrefetch, "Ignoring request with no PC.\n");
return;
}
Addr address = pfi.getAddr();
Addr pc = pfi.getPC();
// Look up table entry, is_secure is unused in findEntry because we
// index using the pc
DCPTEntry *entry = table.findEntry(pc, false /* unused */);
if (entry != nullptr) {
entry->addAddress(address, deltaBits);
//Delta correlating
entry->getCandidates(addresses, deltaMaskBits);
} else {
entry = table.findVictim(pc);
table.insertEntry(pc, false /* unused */, entry);
entry->lastAddress = address;
}
}
DeltaCorrelatingPredictionTables *
DeltaCorrelatingPredictionTablesParams::create()
{
return new DeltaCorrelatingPredictionTables(this);
}
DCPTPrefetcher::DCPTPrefetcher(const DCPTPrefetcherParams *p)
: QueuedPrefetcher(p), dcpt(*p->dcpt)
{
}
void
DCPTPrefetcher::calculatePrefetch(const PrefetchInfo &pfi,
std::vector<AddrPriority> &addresses)
{
dcpt.calculatePrefetch(pfi, addresses);
}
DCPTPrefetcher*
DCPTPrefetcherParams::create()
{
return new DCPTPrefetcher(this);
}
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