The write allocator inspects write packets and detects streaming patterns. More...

#include <base.hh>

Inheritance diagram for gem5::WriteAllocator:

Public Member Functions
	WriteAllocator (const WriteAllocatorParams &p)

bool	coalesce () const
	Should writes be coalesced? This is true if the mode is set to NO_ALLOCATE.

bool	allocate () const
	Should writes allocate?

void	reset ()
	Reset the write allocator state, meaning that it allocates for writes and has not recorded any information about qualifying writes that might trigger a switch to coalescing and later no allocation.

bool	delay (Addr blk_addr)
	Access whether we need to delay the current write.

void	resetDelay (Addr blk_addr)
	Clear delay counter for the input block.

void	updateMode (Addr write_addr, unsigned write_size, Addr blk_addr)
	Update the write mode based on the current write packet.

Public Member Functions inherited from gem5::SimObject
const Params &	params () 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.

virtual void	loadState (CheckpointIn &cp)
	loadState() is called on each SimObject when restoring from a checkpoint.

virtual void	initState ()
	initState() is called on each SimObject when not restoring from a checkpoint.

virtual void	regProbePoints ()
	Register probe points for this object.

virtual void	regProbeListeners ()
	Register probe listeners for this object.

ProbeManager *	getProbeManager ()
	Get the probe manager for this object.

virtual Port &	getPort (const std::string &if_name, PortID idx=InvalidPortID)
	Get a port with a given name and index.

virtual void	startup ()
	startup() is the final initialization call before simulation.

DrainState	drain () override
	Provide a default implementation of the drain interface for objects that don't need draining.

virtual void	memWriteback ()
	Write back dirty buffers to memory using functional writes.

virtual void	memInvalidate ()
	Invalidate the contents of memory buffers.

void	serialize (CheckpointOut &cp) const override
	Serialize an object.

void	unserialize (CheckpointIn &cp) override
	Unserialize an object.

Public Member Functions inherited from gem5::EventManager
EventQueue *	eventQueue () 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.

void	setCurTick (Tick newVal)

	EventManager (EventManager &em)
	Event manger manages events in the event queue.

	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.

void	serializeSection (CheckpointOut &cp, const std::string &name) const

void	unserializeSection (CheckpointIn &cp, const char *name)
	Unserialize an a child object.

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.

virtual void	notifyFork ()
	Notify a child process of a fork.

Public Member Functions inherited from gem5::statistics::Group
	Group (Group parent, const char name=nullptr)
	Construct a new statistics group.

virtual	~Group ()

virtual void	regStats ()
	Callback to set stat parameters.

virtual void	resetStats ()
	Callback to reset stats.

virtual void	preDumpStats ()
	Callback before stats are dumped.

void	addStat (statistics::Info *info)
	Register a stat with this group.

const std::map< std::string, Group * > &	getStatGroups () const
	Get all child groups associated with this object.

const std::vector< Info * > &	getStats () const
	Get all stats associated with this object.

void	addStatGroup (const char name, Group block)
	Add a stat block as a child of this block.

const Info *	resolveStat (std::string name) const
	Resolve a stat by its name within this group.

void	mergeStatGroup (Group *block)
	Merge the contents (stats & children) of a block to this block.

	Group ()=delete

	Group (const Group &)=delete

Group &	operator= (const Group &)=delete

Public Member Functions inherited from gem5::Named
	Named (const std::string &name_)

virtual	~Named ()=default

virtual std::string	name () const

Private Types
enum class	WriteMode : char { ALLOCATE , COALESCE , NO_ALLOCATE }
	The current mode for write coalescing and allocation, either normal operation (ALLOCATE), write coalescing (COALESCE), or write coalescing without allocation (NO_ALLOCATE). More...

Private Attributes
WriteMode	mode

Addr	nextAddr
	Address to match writes against to detect streams.

uint32_t	byteCount
	Bytes written contiguously.

const uint32_t	coalesceLimit
	Limits for when to switch between the different write modes.

const uint32_t	noAllocateLimit

const uint32_t	delayThreshold
	The number of times the allocator will delay an WriteReq MSHR.

std::unordered_map< Addr, Counter >	delayCtr
	Keep track of the number of times the allocator has delayed an WriteReq MSHR.

Additional Inherited Members
Public Types inherited from gem5::SimObject
typedef SimObjectParams	Params

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.

static SimObject *	find (const char *name)
	Find the SimObject with the given name and return a pointer to it.

static void	setSimObjectResolver (SimObjectResolver *resolver)
	There is a single object name resolver, and it is only set when simulation is restoring from checkpoints.

static SimObjectResolver *	getSimObjectResolver ()
	There is a single object name resolver, and it is only set when simulation is restoring from checkpoints.

Static Public Member Functions inherited from gem5::Serializable
static const std::string &	currentSection ()
	Gets the fully-qualified name of the active section.

static void	generateCheckpointOut (const std::string &cpt_dir, std::ofstream &outstream)
	Generate a checkpoint file so that the serialization can be routed to it.

Protected Member Functions inherited from gem5::Drainable
	Drainable ()

virtual	~Drainable ()

virtual void	drainResume ()
	Resume execution after a successful drain.

void	signalDrainDone () const
	Signal that an object is drained.

Protected Attributes inherited from gem5::SimObject
const SimObjectParams &	_params
	Cached copy of the object parameters.

Protected Attributes inherited from gem5::EventManager
EventQueue *	eventq
	A pointer to this object's event queue.

Detailed Description

The write allocator inspects write packets and detects streaming patterns.

The write allocator supports a single stream where writes are expected to access consecutive locations and keeps track of size of the area covered by the concecutive writes in byteCount.

1) When byteCount has surpassed the coallesceLimit the mode switches from ALLOCATE to COALESCE where writes should be delayed until the whole block is written at which point a single packet (whole line write) can service them.

2) When byteCount has also exceeded the noAllocateLimit (whole line) we switch to NO_ALLOCATE when writes should not allocate in the cache but rather send a whole line write to the memory below.

Definition at line 1387 of file base.hh.

Member Enumeration Documentation

◆ WriteMode

enum class gem5::WriteAllocator::WriteMode : char

strongprivate

The current mode for write coalescing and allocation, either normal operation (ALLOCATE), write coalescing (COALESCE), or write coalescing without allocation (NO_ALLOCATE).

Enumerator
ALLOCATE
COALESCE
NO_ALLOCATE

Definition at line 1472 of file base.hh.

Constructor & Destructor Documentation

◆ WriteAllocator()

gem5::WriteAllocator::WriteAllocator ( const WriteAllocatorParams & p )

inline

Definition at line 1390 of file base.hh.

References reset().

Member Function Documentation

◆ allocate()

bool gem5::WriteAllocator::allocate ( ) const

inline

Should writes allocate?

Returns: return true if the cache should not allocate for writes.

Definition at line 1414 of file base.hh.

References mode, and NO_ALLOCATE.

Referenced by gem5::Cache::handleAtomicReqMiss(), and gem5::BaseCache::recvTimingResp().

◆ coalesce()

bool gem5::WriteAllocator::coalesce ( ) const

inline

Should writes be coalesced? This is true if the mode is set to NO_ALLOCATE.

Returns: return true if the cache should coalesce writes.

Definition at line 1405 of file base.hh.

References ALLOCATE, and mode.

Referenced by gem5::BaseCache::coalesce(), and gem5::BaseCache::sendMSHRQueuePacket().

◆ delay()

bool gem5::WriteAllocator::delay ( Addr blk_addr )

inline

Access whether we need to delay the current write.

Parameters

blk_addr The block address the packet writes to

Returns: true if the current packet should be delayed

Definition at line 1436 of file base.hh.

References delayCtr.

Referenced by gem5::BaseCache::sendMSHRQueuePacket().

◆ reset()

void gem5::WriteAllocator::reset ( )

inline

Reset the write allocator state, meaning that it allocates for writes and has not recorded any information about qualifying writes that might trigger a switch to coalescing and later no allocation.

Definition at line 1424 of file base.hh.

References ALLOCATE, byteCount, mode, and nextAddr.

Referenced by gem5::BaseCache::sendMSHRQueuePacket(), and WriteAllocator().

◆ resetDelay()

void gem5::WriteAllocator::resetDelay ( Addr blk_addr )

inline

Clear delay counter for the input block.

Parameters

blk_addr The accessed cache block

Definition at line 1450 of file base.hh.

References delayCtr.

Referenced by gem5::BaseCache::sendMSHRQueuePacket().

◆ updateMode()

void gem5::WriteAllocator::updateMode	(	Addr	write_addr,
		unsigned	write_size,
		Addr	blk_addr )

Update the write mode based on the current write packet.

This method compares the packet's address with any current stream, and updates the tracking and the mode accordingly.

Parameters

write_addr	Start address of the write request
write_size	Size of the write request
blk_addr	The block address that this packet writes to

Definition at line 2717 of file base.cc.

References DPRINTF, and gem5::ArmISA::mode.

Referenced by gem5::BaseCache::handleTimingReqMiss().

Member Data Documentation

◆ byteCount

uint32_t gem5::WriteAllocator::byteCount

private

Bytes written contiguously.

Saturating once we no longer allocate.

Definition at line 1487 of file base.hh.

Referenced by reset().

◆ coalesceLimit

const uint32_t gem5::WriteAllocator::coalesceLimit

private

Limits for when to switch between the different write modes.

Definition at line 1492 of file base.hh.

◆ delayCtr

std::unordered_map<Addr, Counter> gem5::WriteAllocator::delayCtr

private

Keep track of the number of times the allocator has delayed an WriteReq MSHR.

Definition at line 1503 of file base.hh.

Referenced by delay(), and resetDelay().

◆ delayThreshold

const uint32_t gem5::WriteAllocator::delayThreshold

private

The number of times the allocator will delay an WriteReq MSHR.

Definition at line 1497 of file base.hh.

◆ mode

WriteMode gem5::WriteAllocator::mode

private

Definition at line 1478 of file base.hh.

Referenced by allocate(), coalesce(), and reset().

◆ nextAddr

Addr gem5::WriteAllocator::nextAddr

private

Address to match writes against to detect streams.

Definition at line 1481 of file base.hh.

Referenced by reset().

◆ noAllocateLimit

const uint32_t gem5::WriteAllocator::noAllocateLimit

private

Definition at line 1493 of file base.hh.

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

mem/cache/base.hh
mem/cache/base.cc

Public Member Functions

Private Types

Private Attributes

Additional Inherited Members

Detailed Description

Member Enumeration Documentation

◆ WriteMode

Constructor & Destructor Documentation

◆ WriteAllocator()

Member Function Documentation

◆ allocate()

◆ coalesce()

◆ delay()

◆ reset()

◆ resetDelay()

◆ updateMode()

Member Data Documentation

◆ byteCount

◆ coalesceLimit

◆ delayCtr

◆ delayThreshold

◆ mode

◆ nextAddr

◆ noAllocateLimit