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mem-cache: Sandbox Based Optimal Offset Implementation

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Brown, N. T., & Sendag, R. Sandbox Based Optimal Offset Estimation.

Change-Id: Ieb693b6b2c3d8bdfb6948389ca10e92c85454862
Reviewed-on: https://gem5-review.googlesource.com/c/15095
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
This commit is contained in:
Ivan Pizarro
2018-12-13 23:33:48 +01:00
parent 38560efd8b
commit 365ed5b916
4 changed files with 317 additions and 0 deletions
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10
src/mem/cache/prefetch/Prefetcher.py vendored
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@@ -363,3 +363,13 @@ class BOPPrefetcher(QueuedPrefetcher):
delay_queue_cycles = Param.Cycles(60,
"Cycles to delay a write in the left RR table from the delay \
queue")
class SBOOEPrefetcher(QueuedPrefetcher):
type = 'SBOOEPrefetcher'
cxx_class = 'SBOOEPrefetcher'
cxx_header = "mem/cache/prefetch/sbooe.hh"
latency_buffer_size = Param.Int(32, "Entries in the latency buffer")
sequential_prefetchers = Param.Int(9, "Number of sequential prefetchers")
sandbox_entries = Param.Int(1024, "Size of the address buffer")
score_threshold_pct = Param.Percent(25, "Min. threshold to issue a \
prefetch. The value is the percentage of sandbox entries to use")

1
src/mem/cache/prefetch/SConscript vendored
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@@ -38,6 +38,7 @@ Source('bop.cc')
Source('delta_correlating_prediction_tables.cc')
Source('irregular_stream_buffer.cc')
Source('queued.cc')
Source('sbooe.cc')
Source('signature_path.cc')
Source('signature_path_v2.cc')
Source('slim_ampm.cc')

148
src/mem/cache/prefetch/sbooe.cc vendored Normal file
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@@ -0,0 +1,148 @@
/**
* 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);
}

158
src/mem/cache/prefetch/sbooe.hh vendored Normal file
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@@ -0,0 +1,158 @@
/**
* 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
*/
/**
* Implementation of the 'Sandbox Based Optimal Offset Estimation'
* Reference:
* Brown, N. T., & Sendag, R. Sandbox Based Optimal Offset Estimation.
*/
#ifndef __MEM_CACHE_PREFETCH_SBOOE_HH__
#define __MEM_CACHE_PREFETCH_SBOOE_HH__
#include <deque>
#include <unordered_map>
#include <vector>
#include "mem/cache/prefetch/queued.hh"
#include "mem/packet.hh"
struct SBOOEPrefetcherParams;
class SBOOEPrefetcher : public QueuedPrefetcher
{
private:
/** Prefetcher parameters */
const int latencyBufferSize;
const int sequentialPrefetchers;
/** Threshold used to issue prefetchers */
const unsigned int scoreThreshold;
/**
* Holds the current demand addresses and tick. This is later used to
* calculate the average latency buffer when the address is filled in
* the cache.
*/
std::unordered_map<Addr, Tick> demandAddresses;
/**
* The latency buffer holds the elapsed ticks between the demand and
* the fill in the cache for the latest N accesses which are used to
* calculate the average access latency which is later used to
* predict if a prefetcher would be filled on time if issued.
*/
std::deque<Tick> latencyBuffer;
/** Holds the current average access latency */
Tick averageAccessLatency;
/** Holds the current sum of the latency buffer latency */
Tick latencyBufferSum;
struct SandboxEntry {
/** Cache line predicted by the candidate prefetcher */
Addr line;
/** Tick when the simulated prefetch is expected to be filled */
Tick expectedArrivalTick;
/** To indicate if it was initialized */
bool valid;
SandboxEntry()
: valid(false)
{}
};
struct Sandbox {
/** FIFO queue. Max entries is 'sandboxEntries' */
std::vector<SandboxEntry> entries;
/**
* Accesses during the eval period that were present
* in the sandbox
*/
unsigned int sandboxScore;
/** Hits in the sandbox that wouldn't have been filled on time */
unsigned int lateScore;
/** Index of the oldest entry in the FIFO */
unsigned int index;
/** Sequential stride for this prefetcher */
const int stride;
Sandbox(unsigned int max_entries, int _stride)
: sandboxScore(0), lateScore(0), index(0), stride(_stride)
{
entries.resize(max_entries);
}
/**
* Insert the line address being accessed to the cache into the
* FIFO queue of the sandbox.
* @param line Line address being accessed
* @param tick Tick in which the access is expected to be filled
*/
void insert(Addr line, Tick tick);
/** Calculate the useful score
* @return Useful score of the sandbox. Sandbox score adjusted by
* by the late score
*/
unsigned int score() const {
return (sandboxScore - lateScore);
}
};
std::vector<Sandbox> sandboxes;
/** Current best sandbox */
Sandbox * bestSandbox;
/** Number of accesses notified to the prefetcher */
unsigned int accesses;
/**
* Process an access to the specified line address and update the
* sandbox counters counters.
* @param line Address of the line being accessed
* @return TRUE if the evaluation finished, FALSE otherwise
*/
bool access(Addr line);
/** Update the latency buffer after a prefetch fill */
void notifyFill(const PacketPtr& pkt) override;
public:
SBOOEPrefetcher(const SBOOEPrefetcherParams *p);
void calculatePrefetch(const PrefetchInfo &pfi,
std::vector<AddrPriority> &addresses) override;
};
#endif // __MEM_CACHE_PREFETCH_SBOOE_HH__