A layer is an internal crossbar arbitration point with its own flow control. More...

#include <xbar.hh>

Inheritance diagram for gem5::BaseXBar::Layer< SrcType, DstType >:

Public Member Functions
	Layer (DstType &_port, BaseXBar &_xbar, const std::string &_name)
	Create a layer and give it a name.

DrainState	drain () override
	Drain according to the normal semantics, so that the crossbar can tell the layer to drain, and pass an event to signal back when drained.

const std::string	name () const

bool	tryTiming (SrcType *src_port)
	Determine if the layer accepts a packet from a specific port.

void	succeededTiming (Tick busy_time)
	Deal with a destination port accepting a packet by potentially removing the source port from the retry list (if retrying) and occupying the layer accordingly.

void	failedTiming (SrcType *src_port, Tick busy_time)
	Deal with a destination port not accepting a packet by potentially adding the source port to the retry list (if not already at the front) and occupying the layer accordingly.

void	occupyLayer (Tick until)

void	retryWaiting ()
	Send a retry to the port at the head of waitingForLayer.

void	recvRetry ()
	Handle a retry from a neighbouring module.

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

Protected Member Functions
virtual void	sendRetry (SrcType *retry_port)=0
	Sending the actual retry, in a manner specific to the individual layers.

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.

Private Types
enum	State { IDLE , BUSY , RETRY }
	We declare an enum to track the state of the layer. More...

Private Member Functions
void	releaseLayer ()
	Release the layer after being occupied and return to an idle state where we proceed to send a retry to any potential waiting port, or drain if asked to do so.

Private Attributes
DstType &	port
	The destination port this layer converges at.

BaseXBar &	xbar
	The crossbar this layer is a part of.

std::string	_name

State	state

std::deque< SrcType * >	waitingForLayer
	A deque of ports that retry should be called on because the original send was delayed due to a busy layer.

SrcType *	waitingForPeer
	Track who is waiting for the retry when receiving it from a peer.

EventFunctionWrapper	releaseEvent

statistics::Scalar	occupancy
	Stats for occupancy and utilization.

statistics::Formula	utilization

Detailed Description

template<typename SrcType, typename DstType>
class gem5::BaseXBar::Layer< SrcType, DstType >

A layer is an internal crossbar arbitration point with its own flow control.

Each layer is a converging multiplexer tree. By instantiating one layer per destination port (and per packet type, i.e. request, response, snoop request and snoop response), we model full crossbar structures like AXI, ACE, PCIe, etc.

The template parameter, PortClass, indicates the destination port type for the layer. The retry list holds either memory-side ports or CPU-side ports, depending on the direction of the layer. Thus, a request layer has a retry list containing CPU-side ports, whereas a response layer holds memory-side ports.

Definition at line 91 of file xbar.hh.

Member Enumeration Documentation

◆ State

template<typename SrcType , typename DstType >

enum gem5::BaseXBar::Layer::State

private

We declare an enum to track the state of the layer.

The starting point is an idle state where the layer is waiting for a packet to arrive. Upon arrival, the layer transitions to the busy state, where it remains either until the packet transfer is done, or the header time is spent. Once the layer leaves the busy state, it can either go back to idle, if no packets have arrived while it was busy, or the layer goes on to retry the first port in waitingForLayer. A similar transition takes place from idle to retry if the layer receives a retry from one of its connected ports. The retry state lasts until the port in questions calls sendTiming and returns control to the layer, or goes to a busy state if the port does not immediately react to the retry by calling sendTiming.

Enumerator
IDLE
BUSY
RETRY

Definition at line 203 of file xbar.hh.

Constructor & Destructor Documentation

◆ Layer()

template<typename SrcType , typename DstType >

gem5::BaseXBar::Layer< SrcType, DstType >::Layer	(	DstType &	_port,
		BaseXBar &	_xbar,
		const std::string &	_name )

Create a layer and give it a name.

The layer uses the crossbar an event manager.

Parameters

_port	destination port the layer converges at
_xbar	the crossbar this layer belongs to
_name	the layer's name

Definition at line 146 of file xbar.cc.

Member Function Documentation

◆ drain()

template<typename SrcType , typename DstType >

DrainState gem5::BaseXBar::Layer< SrcType, DstType >::drain ( )

overridevirtual

Drain according to the normal semantics, so that the crossbar can tell the layer to drain, and pass an event to signal back when drained.

Parameters

de	drain event to call once drained

Returns: 1 if busy or waiting to retry, or 0 if idle

Implements gem5::Drainable.

Definition at line 598 of file xbar.cc.

References DPRINTF, gem5::Drained, gem5::Draining, and state.

◆ failedTiming()

template<typename SrcType , typename DstType >

void gem5::BaseXBar::Layer< SrcType, DstType >::failedTiming	(	SrcType *	src_port,
		Tick	busy_time )

Deal with a destination port not accepting a packet by potentially adding the source port to the retry list (if not already at the front) and occupying the layer accordingly.

Parameters

src_port	Source port
busy_time	Time to spend as a result of a failed send

Definition at line 229 of file xbar.cc.

References gem5::scmi::BUSY, and state.

◆ name()

template<typename SrcType , typename DstType >

const std::string gem5::BaseXBar::Layer< SrcType, DstType >::name ( ) const

inline

Definition at line 117 of file xbar.hh.

References gem5::BaseXBar::Layer< SrcType, DstType >::_name.

◆ occupyLayer()

template<typename SrcType , typename DstType >

void gem5::BaseXBar::Layer< SrcType, DstType >::occupyLayer ( Tick until )

Definition at line 165 of file xbar.cc.

References gem5::scmi::BUSY, gem5::curTick(), DPRINTF, and state.

◆ recvRetry()

template<typename SrcType , typename DstType >

void gem5::BaseXBar::Layer< SrcType, DstType >::recvRetry ( )

Handle a retry from a neighbouring module.

This wraps retryWaiting by verifying that there are ports waiting before calling retryWaiting.

Definition at line 310 of file xbar.cc.

References gem5::scmi::BUSY, and state.

◆ releaseLayer()

template<typename SrcType , typename DstType >

void gem5::BaseXBar::Layer< SrcType, DstType >::releaseLayer ( )

private

Release the layer after being occupied and return to an idle state where we proceed to send a retry to any potential waiting port, or drain if asked to do so.

Definition at line 251 of file xbar.cc.

References gem5::scmi::BUSY, DPRINTF, gem5::Draining, and state.

◆ retryWaiting()

template<typename SrcType , typename DstType >

void gem5::BaseXBar::Layer< SrcType, DstType >::retryWaiting ( )

Send a retry to the port at the head of waitingForLayer.

The caller must ensure that the list is not empty.

Definition at line 275 of file xbar.cc.

References gem5::scmi::BUSY, and state.

◆ sendRetry()

template<typename SrcType , typename DstType >

virtual void gem5::BaseXBar::Layer< SrcType, DstType >::sendRetry ( SrcType * retry_port )

protectedpure virtual

Sending the actual retry, in a manner specific to the individual layers.

Note that for a RequestPort, there is both a RequestLayer and a SnoopResponseLayer using the same port, but using different functions for the flow control.

Implemented in gem5::BaseXBar::ReqLayer, gem5::BaseXBar::RespLayer, and gem5::BaseXBar::SnoopRespLayer.

◆ succeededTiming()

template<typename SrcType , typename DstType >

void gem5::BaseXBar::Layer< SrcType, DstType >::succeededTiming ( Tick busy_time )

Deal with a destination port accepting a packet by potentially removing the source port from the retry list (if retrying) and occupying the layer accordingly.

Parameters

busy_time Time to spend as a result of a successful send

Definition at line 217 of file xbar.cc.

References gem5::scmi::BUSY, and state.

◆ tryTiming()

template<typename SrcType , typename DstType >

bool gem5::BaseXBar::Layer< SrcType, DstType >::tryTiming ( SrcType * src_port )

Determine if the layer accepts a packet from a specific port.

If not, the port in question is also added to the retry list. In either case the state of the layer is updated accordingly.

Parameters

port	Source port presenting the packet

Returns: True if the layer accepts the packet

Definition at line 186 of file xbar.cc.

References gem5::scmi::BUSY, and state.

Member Data Documentation

◆ _name

template<typename SrcType , typename DstType >

std::string gem5::BaseXBar::Layer< SrcType, DstType >::_name

private

Definition at line 185 of file xbar.hh.

Referenced by gem5::BaseXBar::Layer< SrcType, DstType >::name().

◆ occupancy

template<typename SrcType , typename DstType >

statistics::Scalar gem5::BaseXBar::Layer< SrcType, DstType >::occupancy

private

Stats for occupancy and utilization.

These stats capture the time the layer spends in the busy state and are thus only relevant when the memory system is in timing mode.

Definition at line 232 of file xbar.hh.

◆ port

template<typename SrcType , typename DstType >

DstType& gem5::BaseXBar::Layer< SrcType, DstType >::port

private

The destination port this layer converges at.

Definition at line 180 of file xbar.hh.

◆ releaseEvent

template<typename SrcType , typename DstType >

EventFunctionWrapper gem5::BaseXBar::Layer< SrcType, DstType >::releaseEvent

private

Definition at line 225 of file xbar.hh.

◆ state

template<typename SrcType , typename DstType >

State gem5::BaseXBar::Layer< SrcType, DstType >::state

private

Definition at line 205 of file xbar.hh.

◆ utilization

template<typename SrcType , typename DstType >

statistics::Formula gem5::BaseXBar::Layer< SrcType, DstType >::utilization

private

Definition at line 233 of file xbar.hh.

◆ waitingForLayer

template<typename SrcType , typename DstType >

std::deque<SrcType*> gem5::BaseXBar::Layer< SrcType, DstType >::waitingForLayer

private

A deque of ports that retry should be called on because the original send was delayed due to a busy layer.

Definition at line 211 of file xbar.hh.

◆ waitingForPeer

template<typename SrcType , typename DstType >

SrcType* gem5::BaseXBar::Layer< SrcType, DstType >::waitingForPeer

private

Track who is waiting for the retry when receiving it from a peer.

If no port is waiting NULL is stored.

Definition at line 217 of file xbar.hh.

◆ xbar

template<typename SrcType , typename DstType >

BaseXBar& gem5::BaseXBar::Layer< SrcType, DstType >::xbar

private

The crossbar this layer is a part of.

Definition at line 183 of file xbar.hh.

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

mem/xbar.hh
mem/xbar.cc

Public Member Functions

Protected Member Functions

Private Types

Private Member Functions

Private Attributes

Detailed Description

Member Enumeration Documentation

◆ State

Constructor & Destructor Documentation

◆ Layer()

Member Function Documentation

◆ drain()

◆ failedTiming()

◆ name()

◆ occupyLayer()

◆ recvRetry()

◆ releaseLayer()

◆ retryWaiting()

◆ sendRetry()

◆ succeededTiming()

◆ tryTiming()

Member Data Documentation

◆ _name

◆ occupancy

◆ port

◆ releaseEvent

◆ state

◆ utilization

◆ waitingForLayer

◆ waitingForPeer

◆ xbar