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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: Ivan Pizarro
*/
#include "mem/cache/prefetch/sbooe.hh"
#include "debug/HWPrefetch.hh"
#include "params/SBOOEPrefetcher.hh"
SBOOEPrefetcher::SBOOEPrefetcher(const SBOOEPrefetcherParams *p)
: QueuedPrefetcher(p),
latencyBufferSize(p->latency_buffer_size),
sequentialPrefetchers(p->sequential_prefetchers),
scoreThreshold((p->sandbox_entries*p->score_threshold_pct)/100),
averageAccessLatency(0), latencyBufferSum(0),
bestSandbox(NULL),
accesses(0)
{
if (!(p->score_threshold_pct >= 0 && p->score_threshold_pct <= 100)) {
fatal("%s: the score threshold should be between 0 and 100\n", name());
}
// Initialize a sandbox for every sequential prefetcher between
// -1 and the number of sequential prefetchers defined
for (int i = 0; i < sequentialPrefetchers; i++) {
sandboxes.push_back(Sandbox(p->sandbox_entries, i-1));
}
}
void
SBOOEPrefetcher::Sandbox::insert(Addr addr, Tick tick)
{
entries[index].valid = true;
entries[index].line = addr + stride;
entries[index].expectedArrivalTick = tick;
index++;
if (index == entries.size()) {
index = 0;
}
}
bool
SBOOEPrefetcher::access(Addr access_line)
{
for (Sandbox &sb : sandboxes) {
// Search for the address in the FIFO queue
for (const SandboxEntry &entry: sb.entries) {
if (entry.valid && entry.line == access_line) {
sb.sandboxScore++;
if (entry.expectedArrivalTick > curTick()) {
sb.lateScore++;
}
}
}
sb.insert(access_line, curTick() + averageAccessLatency);
if (bestSandbox == NULL || sb.score() > bestSandbox->score()) {
bestSandbox = &sb;
}
}
accesses++;
return (accesses >= sandboxes.size());
}
void
SBOOEPrefetcher::notifyFill(const PacketPtr& pkt)
{
// (1) Look for the address in the demands list
// (2) Calculate the elapsed cycles until it was filled (curTick)
// (3) Insert the latency into the latency buffer (FIFO)
// (4) Calculate the new average access latency
auto it = demandAddresses.find(pkt->getAddr());
if (it != demandAddresses.end()) {
Tick elapsed_ticks = curTick() - it->second;
latencyBuffer.push_back(elapsed_ticks);
latencyBufferSum += elapsed_ticks;
if (latencyBuffer.size() > latencyBufferSize) {
latencyBufferSum -= latencyBuffer.front();
latencyBuffer.pop_front();
}
averageAccessLatency = latencyBufferSum / latencyBuffer.size();
demandAddresses.erase(it);
}
}
void
SBOOEPrefetcher::calculatePrefetch(const PrefetchInfo &pfi,
std::vector<AddrPriority> &addresses)
{
const Addr pfi_addr = pfi.getAddr();
const Addr pfi_line = pfi_addr >> lBlkSize;
auto it = demandAddresses.find(pfi_addr);
if (it == demandAddresses.end()) {
demandAddresses.insert(std::pair<Addr, Tick>(pfi_addr, curTick()));
}
const bool evaluationFinished = access(pfi_line);
if (evaluationFinished && bestSandbox->score() > scoreThreshold) {
Addr pref_line = pfi_line + bestSandbox->stride;
addresses.push_back(AddrPriority(pref_line << lBlkSize, 0));
}
}
SBOOEPrefetcher*
SBOOEPrefetcherParams::create()
{
return new SBOOEPrefetcher(this);
}
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