gem5  v21.1.0.2
Public Types | Public Member Functions | Private Member Functions | Private Attributes | List of all members
gem5::SkewedAssociative Class Reference

A skewed associative indexing policy. More...

#include <skewed_associative.hh>

Inheritance diagram for gem5::SkewedAssociative:
gem5::BaseIndexingPolicy gem5::SimObject gem5::EventManager gem5::Serializable gem5::Drainable gem5::statistics::Group gem5::Named

Public Types

typedef SkewedAssociativeParams Params
 Convenience typedef. More...
 
- Public Types inherited from gem5::BaseIndexingPolicy
typedef BaseIndexingPolicyParams Params
 Convenience typedef. More...
 
- Public Types inherited from gem5::SimObject
typedef SimObjectParams Params
 

Public Member Functions

 SkewedAssociative (const Params &p)
 Construct and initialize this policy. More...
 
 ~SkewedAssociative ()
 Destructor. More...
 
std::vector< ReplaceableEntry * > getPossibleEntries (const Addr addr) const override
 Find all possible entries for insertion and replacement of an address. More...
 
Addr regenerateAddr (const Addr tag, const ReplaceableEntry *entry) const override
 Regenerate an entry's address from its tag and assigned set and way. More...
 
- Public Member Functions inherited from gem5::BaseIndexingPolicy
 BaseIndexingPolicy (const Params &p)
 Construct and initialize this policy. More...
 
 ~BaseIndexingPolicy ()
 Destructor. More...
 
void setEntry (ReplaceableEntry *entry, const uint64_t index)
 Associate a pointer to an entry to its physical counterpart. More...
 
ReplaceableEntrygetEntry (const uint32_t set, const uint32_t way) const
 Get an entry based on its set and way. More...
 
virtual Addr extractTag (const Addr addr) const
 Generate the tag from the given address. More...
 
- Public Member Functions inherited from gem5::SimObject
const Paramsparams () const
 
 SimObject (const Params &p)
 
virtual ~SimObject ()
 
virtual void init ()
 init() is called after all C++ SimObjects have been created and all ports are connected. More...
 
virtual void loadState (CheckpointIn &cp)
 loadState() is called on each SimObject when restoring from a checkpoint. More...
 
virtual void initState ()
 initState() is called on each SimObject when not restoring from a checkpoint. More...
 
virtual void regProbePoints ()
 Register probe points for this object. More...
 
virtual void regProbeListeners ()
 Register probe listeners for this object. More...
 
ProbeManagergetProbeManager ()
 Get the probe manager for this object. More...
 
virtual PortgetPort (const std::string &if_name, PortID idx=InvalidPortID)
 Get a port with a given name and index. More...
 
virtual void startup ()
 startup() is the final initialization call before simulation. More...
 
DrainState drain () override
 Provide a default implementation of the drain interface for objects that don't need draining. More...
 
virtual void memWriteback ()
 Write back dirty buffers to memory using functional writes. More...
 
virtual void memInvalidate ()
 Invalidate the contents of memory buffers. More...
 
void serialize (CheckpointOut &cp) const override
 Serialize an object. More...
 
void unserialize (CheckpointIn &cp) override
 Unserialize an object. More...
 
- Public Member Functions inherited from gem5::EventManager
EventQueueeventQueue () const
 
void schedule (Event &event, Tick when)
 
void deschedule (Event &event)
 
void reschedule (Event &event, Tick when, bool always=false)
 
void schedule (Event *event, Tick when)
 
void deschedule (Event *event)
 
void reschedule (Event *event, Tick when, bool always=false)
 
void wakeupEventQueue (Tick when=(Tick) -1)
 This function is not needed by the usual gem5 event loop but may be necessary in derived EventQueues which host gem5 on other schedulers. More...
 
void setCurTick (Tick newVal)
 
 EventManager (EventManager &em)
 Event manger manages events in the event queue. More...
 
 EventManager (EventManager *em)
 
 EventManager (EventQueue *eq)
 
- Public Member Functions inherited from gem5::Serializable
 Serializable ()
 
virtual ~Serializable ()
 
void serializeSection (CheckpointOut &cp, const char *name) const
 Serialize an object into a new section. More...
 
void serializeSection (CheckpointOut &cp, const std::string &name) const
 
void unserializeSection (CheckpointIn &cp, const char *name)
 Unserialize an a child object. More...
 
void unserializeSection (CheckpointIn &cp, const std::string &name)
 
- Public Member Functions inherited from gem5::Drainable
DrainState drainState () const
 Return the current drain state of an object. More...
 
virtual void notifyFork ()
 Notify a child process of a fork. More...
 
- Public Member Functions inherited from gem5::statistics::Group
 Group (Group *parent, const char *name=nullptr)
 Construct a new statistics group. More...
 
virtual ~Group ()
 
virtual void regStats ()
 Callback to set stat parameters. More...
 
virtual void resetStats ()
 Callback to reset stats. More...
 
virtual void preDumpStats ()
 Callback before stats are dumped. More...
 
void addStat (statistics::Info *info)
 Register a stat with this group. More...
 
const std::map< std::string, Group * > & getStatGroups () const
 Get all child groups associated with this object. More...
 
const std::vector< Info * > & getStats () const
 Get all stats associated with this object. More...
 
void addStatGroup (const char *name, Group *block)
 Add a stat block as a child of this block. More...
 
const InforesolveStat (std::string name) const
 Resolve a stat by its name within this group. More...
 
void mergeStatGroup (Group *block)
 Merge the contents (stats & children) of a block to this block. More...
 
 Group ()=delete
 
 Group (const Group &)=delete
 
Groupoperator= (const Group &)=delete
 
- Public Member Functions inherited from gem5::Named
 Named (const std::string &name_)
 
virtual ~Named ()=default
 
virtual std::string name () const
 

Private Member Functions

Addr hash (const Addr addr) const
 The hash function itself. More...
 
Addr dehash (const Addr addr) const
 Inverse of the hash function. More...
 
Addr skew (const Addr addr, const uint32_t way) const
 Address skewing function selection. More...
 
Addr deskew (const Addr addr, const uint32_t way) const
 Address deskewing function (inverse of the skew function) of the given way. More...
 
uint32_t extractSet (const Addr addr, const uint32_t way) const
 Apply a skewing function to calculate address' set given a way. More...
 

Private Attributes

const int NUM_SKEWING_FUNCTIONS = 8
 The number of skewing functions implemented. More...
 
const int msbShift
 The amount to shift a set index to get its MSB. More...
 

Additional Inherited Members

- Static Public Member Functions inherited from gem5::SimObject
static void serializeAll (const std::string &cpt_dir)
 Create a checkpoint by serializing all SimObjects in the system. More...
 
static SimObjectfind (const char *name)
 Find the SimObject with the given name and return a pointer to it. More...
 
static void setSimObjectResolver (SimObjectResolver *resolver)
 There is a single object name resolver, and it is only set when simulation is restoring from checkpoints. More...
 
static SimObjectResolvergetSimObjectResolver ()
 There is a single object name resolver, and it is only set when simulation is restoring from checkpoints. More...
 
- Static Public Member Functions inherited from gem5::Serializable
static const std::string & currentSection ()
 Gets the fully-qualified name of the active section. More...
 
static void generateCheckpointOut (const std::string &cpt_dir, std::ofstream &outstream)
 Generate a checkpoint file so that the serialization can be routed to it. More...
 
- Protected Member Functions inherited from gem5::Drainable
 Drainable ()
 
virtual ~Drainable ()
 
virtual void drainResume ()
 Resume execution after a successful drain. More...
 
void signalDrainDone () const
 Signal that an object is drained. More...
 
- Protected Attributes inherited from gem5::BaseIndexingPolicy
const unsigned assoc
 The associativity. More...
 
const uint32_t numSets
 The number of sets in the cache. More...
 
const int setShift
 The amount to shift the address to get the set. More...
 
const unsigned setMask
 Mask out all bits that aren't part of the set index. More...
 
std::vector< std::vector< ReplaceableEntry * > > sets
 The cache sets. More...
 
const int tagShift
 The amount to shift the address to get the tag. More...
 
- Protected Attributes inherited from gem5::SimObject
const SimObjectParams & _params
 Cached copy of the object parameters. More...
 
- Protected Attributes inherited from gem5::EventManager
EventQueueeventq
 A pointer to this object's event queue. More...
 

Detailed Description

A skewed associative indexing policy.

See also
gem5 Memory System

The skewed indexing policy has a variable mapping based on a hash function, so a value x can be mapped to different sets, based on the way being used.

For example, let's assume address A maps to set 3 on way 0. It will likely have a different set for every other way. Visually, the possible locations of A are, for a table with 4 ways and 8 sets (arbitrarily chosen sets; these locations depend on A and the hashing function used): Way 0 1 2 3 Set _ _ _ _ 0 |_| |_| |X| |_| 1 |_| |_| |_| |X| 2 |_| |_| |_| |_| 3 |X| |_| |_| |_| 4 |_| |_| |_| |_| 5 |_| |X| |_| |_| 6 |_| |_| |_| |_| 7 |_| |_| |_| |_|

If provided with an associativity higher than the number of skewing functions, the skewing functions of the extra ways might be sub-optimal.

Definition at line 72 of file skewed_associative.hh.

Member Typedef Documentation

◆ Params

typedef SkewedAssociativeParams gem5::SkewedAssociative::Params

Convenience typedef.

Definition at line 143 of file skewed_associative.hh.

Constructor & Destructor Documentation

◆ SkewedAssociative()

gem5::SkewedAssociative::SkewedAssociative ( const Params p)

◆ ~SkewedAssociative()

gem5::SkewedAssociative::~SkewedAssociative ( )
inline

Destructor.

Definition at line 153 of file skewed_associative.hh.

Member Function Documentation

◆ dehash()

Addr gem5::SkewedAssociative::dehash ( const Addr  addr) const
private

Inverse of the hash function.

See also
hash().
Parameters
addrThe address to be dehashed.
Thedehashed address.

Definition at line 75 of file skewed_associative.cc.

References gem5::X86ISA::addr, and msbShift.

Referenced by deskew(), and skew().

◆ deskew()

Addr gem5::SkewedAssociative::deskew ( const Addr  addr,
const uint32_t  way 
) const
private

Address deskewing function (inverse of the skew function) of the given way.

See also
skew()
Parameters
addrAddress to be deskewed. Should contain the set and tag bits.
wayThe cache way, used to select a hash function.
Returns
The deskewed address.

Definition at line 142 of file skewed_associative.cc.

References gem5::X86ISA::addr, dehash(), hash(), gem5::ArmISA::i, msbShift, NUM_SKEWING_FUNCTIONS, and panic.

Referenced by regenerateAddr().

◆ extractSet()

uint32_t gem5::SkewedAssociative::extractSet ( const Addr  addr,
const uint32_t  way 
) const
private

Apply a skewing function to calculate address' set given a way.

Parameters
addrThe address to calculate the set for.
wayThe way to get the set from.
Returns
The set index for given combination of address and way.

Definition at line 195 of file skewed_associative.cc.

References gem5::X86ISA::addr, gem5::BaseIndexingPolicy::setMask, gem5::BaseIndexingPolicy::setShift, and skew().

Referenced by getPossibleEntries().

◆ getPossibleEntries()

std::vector< ReplaceableEntry * > gem5::SkewedAssociative::getPossibleEntries ( const Addr  addr) const
overridevirtual

Find all possible entries for insertion and replacement of an address.

Should be called immediately before ReplacementPolicy's findVictim() not to break cache resizing.

Parameters
addrThe addr to a find possible entries for.
Returns
The possible entries.

Implements gem5::BaseIndexingPolicy.

Definition at line 210 of file skewed_associative.cc.

References gem5::X86ISA::addr, gem5::BaseIndexingPolicy::assoc, extractSet(), and gem5::BaseIndexingPolicy::sets.

◆ hash()

Addr gem5::SkewedAssociative::hash ( const Addr  addr) const
private

The hash function itself.

Uses the hash function H, as described in "Skewed-Associative Caches", from Seznec et al. (section 3.3): It applies an XOR to the MSB and LSB, shifts all bits one bit to the right, and set the result of the XOR as the new MSB.

This function is not bijective if the address has only 1 bit, as the MSB and LSB will be the same, and therefore the xor will always be 0.

Parameters
addrThe address to be hashed.
Thehashed address.

Definition at line 63 of file skewed_associative.cc.

References gem5::X86ISA::addr, and msbShift.

Referenced by deskew(), and skew().

◆ regenerateAddr()

Addr gem5::SkewedAssociative::regenerateAddr ( const Addr  tag,
const ReplaceableEntry entry 
) const
overridevirtual

Regenerate an entry's address from its tag and assigned set and way.

Uses the inverse of the skewing function.

Parameters
tagThe tag bits.
entryThe entry.
Returns
the entry's address.

Implements gem5::BaseIndexingPolicy.

Definition at line 201 of file skewed_associative.cc.

References deskew(), gem5::ReplaceableEntry::getSet(), gem5::ReplaceableEntry::getWay(), msbShift, gem5::BaseIndexingPolicy::setMask, gem5::BaseIndexingPolicy::setShift, and gem5::BaseIndexingPolicy::tagShift.

◆ skew()

Addr gem5::SkewedAssociative::skew ( const Addr  addr,
const uint32_t  way 
) const
private

Address skewing function selection.

It selects and applies one of the skewing functions functions based on the way provided.

Parameters
addrAddress to be skewed. Should contain the set and tag bits.
wayThe cache way, used to select a hash function.
Returns
The skewed address.

Definition at line 90 of file skewed_associative.cc.

References gem5::X86ISA::addr, dehash(), hash(), gem5::ArmISA::i, msbShift, NUM_SKEWING_FUNCTIONS, and panic.

Referenced by extractSet().

Member Data Documentation

◆ msbShift

const int gem5::SkewedAssociative::msbShift
private

The amount to shift a set index to get its MSB.

Definition at line 86 of file skewed_associative.hh.

Referenced by dehash(), deskew(), hash(), regenerateAddr(), skew(), and SkewedAssociative().

◆ NUM_SKEWING_FUNCTIONS

const int gem5::SkewedAssociative::NUM_SKEWING_FUNCTIONS = 8
private

The number of skewing functions implemented.

Should be updated if more functions are added. If more than this number of skewing functions are needed (i.e., assoc > this value), we programatically generate new ones, which may be sub-optimal.

Definition at line 81 of file skewed_associative.hh.

Referenced by deskew(), skew(), and SkewedAssociative().


The documentation for this class was generated from the following files:

Generated on Tue Sep 21 2021 12:28:10 for gem5 by doxygen 1.8.17