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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
*/
/**
* Implementation of the Signature Path Prefetcher
*
* References:
* Lookahead prefetching with signature path
* J Kim, PV Gratz, ALN Reddy
* The 2nd Data Prefetching Championship (DPC2)
* The filter feature described in the paper is not implemented, as it
* redundant prefetches are dropped by the cache.
*/
#ifndef __MEM_CACHE_PREFETCH_SIGNATURE_PATH_HH__
#define __MEM_CACHE_PREFETCH_SIGNATURE_PATH_HH__
#include "mem/cache/prefetch/associative_set.hh"
#include "mem/cache/prefetch/queued.hh"
#include "mem/packet.hh"
struct SignaturePathPrefetcherParams;
class SignaturePathPrefetcher : public QueuedPrefetcher
{
/** Signature type */
typedef uint16_t signature_t;
/** Stride type */
typedef int16_t stride_t;
/** Number of strides stored in each pattern entry */
const unsigned stridesPerPatternEntry;
/** Number of bits to shift when generating a new signature */
const uint8_t signatureShift;
/** Size of the signature, in bits */
const signature_t signatureBits;
/** Maximum pattern entries counter value */
const uint8_t maxCounterValue;
/** Minimum confidence to issue a prefetch */
const double prefetchConfidenceThreshold;
/** Minimum confidence to keep navigating lookahead entries */
const double lookaheadConfidenceThreshold;
/** Signature entry data type */
struct SignatureEntry : public TaggedEntry
{
/** Path signature */
signature_t signature;
/** Last accessed block within a page */
stride_t lastBlock;
SignatureEntry() : signature(0), lastBlock(0)
{}
};
/** Signature table */
AssociativeSet<SignatureEntry> signatureTable;
/** A stride entry with its counter */
struct PatternStrideEntry
{
/** stride in a page in blkSize increments */
stride_t stride;
/** counter value (max value defined by maxCounterValue) */
uint8_t counter;
PatternStrideEntry() : stride(0), counter(0)
{}
};
/** Pattern entry data type, a set of stride and counter entries */
struct PatternEntry : public TaggedEntry
{
/** group of stides */
std::vector<PatternStrideEntry> strideEntries;
PatternEntry(size_t num_strides) : strideEntries(num_strides)
{}
/** Reset the entries to their initial values */
void reset() override
{
for (auto &entry : strideEntries) {
entry.counter = 0;
entry.stride = 0;
}
}
/**
* Returns the entry with the desired stride
* @param stride the stride to find
* @result a pointer to the entry, if the stride was found, or nullptr,
* if the stride was not found
*/
PatternStrideEntry *findStride(stride_t stride)
{
PatternStrideEntry *found_entry = nullptr;
for (auto &entry : strideEntries) {
if (entry.stride == stride) {
found_entry = &entry;
break;
}
}
return found_entry;
}
/**
* Gets the entry with the provided stride, if there is no entry with
* the associated stride, it replaces one of them.
* @param stride the stride to find
* @param max_counter_value maximum value of the confidence counters,
* it is used when no strides are found and an entry needs to be
* replaced
* @result reference to the selected entry
*/
PatternStrideEntry &getStrideEntry(stride_t stride,
uint8_t max_counter_value);
};
/** Pattern table */
AssociativeSet<PatternEntry> patternTable;
/**
* Generates a new signature from an existing one and a new stride
* @param sig current signature
* @param str stride to add to the new signature
* @result the new signature
*/
inline signature_t updateSignature(signature_t sig, stride_t str) const {
sig <<= signatureShift;
sig ^= str;
sig &= mask(signatureBits);
return sig;
}
/**
* Generates an address to be prefetched.
* @param ppn page number to prefetch from
* @param block block number within the page, this value can be negative,
* which means that the block refered is actualy in the previous
* page (ppn-1), if the value is greater than (pageBytes/blkSize-1)
* then the block refers to a block within the next page (ppn+1)
* @param is_secure whether this page is inside the secure memory area
* @param addresses if allowed, the address will be added to this vector
*/
void addPrefetch(Addr ppn, stride_t block, bool is_secure,
std::vector<AddrPriority> &addresses);
/**
* Obtains the SignatureEntry of the given page, if the page is not found,
* it allocates a new one, replacing an existing entry if needed
* @param ppn physical page number of the page
* @param is_secure whether this page is inside the secure memory area
* @param block accessed block within the page
* @param miss output, if the entry is not found, this will be set to true
* @result a reference to the SignatureEntry
*/
SignatureEntry & getSignatureEntry(Addr ppn, bool is_secure,
stride_t block, bool &miss);
/**
* Obtains the PatternEntry of the given signature, if the signature is
* not found, it allocates a new one, replacing an existing entry if needed
* @param signature the signature of the desired entry
* @result a reference to the PatternEntry
*/
PatternEntry & getPatternEntry(Addr signature);
/**
* Updates the pattern table with the provided signature and stride
* @param signature the signature to use to index the pattern table
* @param stride the stride to use to index the set of strides of the
* pattern table entry
*/
void updatePatternTable(Addr signature, stride_t stride);
public:
SignaturePathPrefetcher(const SignaturePathPrefetcherParams* p);
~SignaturePathPrefetcher() {}
void calculatePrefetch(const PrefetchInfo &pfi,
std::vector<AddrPriority> &addresses) override;
};
#endif//__MEM_CACHE_PREFETCH_SIGNATURE_PATH_HH__
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