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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/signature_path_v2.hh"
#include <cassert>
#include "debug/HWPrefetch.hh"
#include "mem/cache/prefetch/associative_set_impl.hh"
#include "params/SignaturePathPrefetcherV2.hh"
SignaturePathPrefetcherV2::SignaturePathPrefetcherV2(
const SignaturePathPrefetcherV2Params *p)
: SignaturePathPrefetcher(p),
globalHistoryRegister(p->global_history_register_entries,
p->global_history_register_entries,
p->global_history_register_indexing_policy,
p->global_history_register_replacement_policy,
GlobalHistoryEntry())
{
}
void
SignaturePathPrefetcherV2::handleSignatureTableMiss(stride_t current_block,
signature_t &new_signature, double &new_conf, stride_t &new_stride)
{
bool found = false;
// This should return all entries of the GHR, since it is a fully
// associative table
std::vector<GlobalHistoryEntry *> all_ghr_entries =
globalHistoryRegister.getPossibleEntries(0 /* any value works */);
for (auto gh_entry : all_ghr_entries) {
if (gh_entry->lastBlock + gh_entry->delta == current_block) {
new_signature = gh_entry->signature;
new_conf = gh_entry->confidence;
new_stride = gh_entry->delta;
found = true;
globalHistoryRegister.accessEntry(gh_entry);
break;
}
}
if (!found) {
new_signature = current_block;
new_conf = 1.0;
new_stride = current_block;
}
}
double
SignaturePathPrefetcherV2::calculateLookaheadConfidence(
PatternEntry const &sig, PatternStrideEntry const &lookahead) const
{
if (sig.counter == 0) return 0.0;
return (((double) usefulPrefetches) / issuedPrefetches) *
(((double) lookahead.counter) / sig.counter);
}
double
SignaturePathPrefetcherV2::calculatePrefetchConfidence(PatternEntry const &sig,
PatternStrideEntry const &entry) const
{
if (sig.counter == 0) return 0.0;
return ((double) entry.counter) / sig.counter;
}
void
SignaturePathPrefetcherV2::increasePatternEntryCounter(
PatternEntry &pattern_entry, PatternStrideEntry &pstride_entry)
{
if (pattern_entry.counter == maxCounterValue) {
pattern_entry.counter >>= 1;
for (auto &entry : pattern_entry.strideEntries) {
entry.counter >>= 1;
}
}
if (pstride_entry.counter == maxCounterValue) {
pattern_entry.counter >>= 1;
for (auto &entry : pattern_entry.strideEntries) {
entry.counter >>= 1;
}
}
pattern_entry.counter += 1;
pstride_entry.counter += 1;
}
void
SignaturePathPrefetcherV2::handlePageCrossingLookahead(signature_t signature,
stride_t last_offset, stride_t delta, double path_confidence)
{
// Always use the replacement policy to assign new entries, as all
// of them are unique, there are never "hits" in the GHR
GlobalHistoryEntry *gh_entry = globalHistoryRegister.findVictim(0);
assert(gh_entry != nullptr);
// Any address value works, as it is never used
globalHistoryRegister.insertEntry(0, false, gh_entry);
gh_entry->signature = signature;
gh_entry->lastBlock = last_offset;
gh_entry->delta = delta;
gh_entry->confidence = path_confidence;
}
SignaturePathPrefetcherV2*
SignaturePathPrefetcherV2Params::create()
{
return new SignaturePathPrefetcherV2(this);
}
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