This snoop filter keeps track of which connected port has a particular line of data. More...

#include <snoop_filter.hh>

Inheritance diagram for SnoopFilter:

Classes
struct	SnoopItem
	Per cache line item tracking a bitmask of SlavePorts who have an outstanding request to this line (requested) or already share a cache line with this address (holder). More...

Public Types
typedef std::vector < QueuedSlavePort * >	SnoopList

Public Types inherited from SimObject
typedef SimObjectParams	Params

Public Member Functions
	SnoopFilter (const SnoopFilterParams *p)

void	setSlavePorts (const SnoopList &slave_ports)
	Init a new snoop filter and tell it about all the slave ports of the enclosing bus. More...

std::pair< SnoopList, Cycles >	lookupRequest (const Packet *cpkt, const SlavePort &slave_port)
	Lookup a request (from a slave port) in the snoop filter and return a list of other slave ports that need forwarding of the resulting snoops. More...

void	finishRequest (bool will_retry, Addr addr, bool is_secure)
	For an un-successful request, revert the change to the snoop filter. More...

std::pair< SnoopList, Cycles >	lookupSnoop (const Packet *cpkt)
	Handle an incoming snoop from below (the master port). More...

void	updateSnoopResponse (const Packet *cpkt, const SlavePort &rsp_port, const SlavePort &req_port)
	Let the snoop filter see any snoop responses that turn into request responses and indicate cache to cache transfers. More...

void	updateSnoopForward (const Packet *cpkt, const SlavePort &rsp_port, const MasterPort &req_port)
	Pass snoop responses that travel downward through the snoop filter and let them update the snoop filter state. More...

void	updateResponse (const Packet *cpkt, const SlavePort &slave_port)
	Update the snoop filter with a response from below (outer / other cache, or memory) and update the tracking information in the snoop filter. More...

virtual void	regStats ()
	Register statistics for this object. More...

Public Member Functions inherited from SimObject
const Params *	params () const

	SimObject (const Params *_params)

virtual	~SimObject ()

virtual const std::string	name () const

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	resetStats ()
	Reset statistics associated with this object. More...

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

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

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

	EventManager (EventManager *em)

	EventManager (EventQueue *eq)

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)

void	setCurTick (Tick newVal)

Public Member Functions inherited from 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 Drainable
DrainState	drainState () const
	Return the current drain state of an object. More...

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

Protected Types
typedef uint64_t	SnoopMask
	The underlying type for the bitmask we use for tracking. More...

typedef std::unordered_map < Addr, SnoopItem >	SnoopFilterCache
	HashMap of SnoopItems indexed by line address. More...

Protected Member Functions
std::pair< SnoopList, Cycles >	snoopAll (Cycles latency) const
	Simple factory methods for standard return values. More...

std::pair< SnoopList, Cycles >	snoopSelected (const SnoopList &slave_ports, Cycles latency) const

std::pair< SnoopList, Cycles >	snoopDown (Cycles latency) const

SnoopMask	portToMask (const SlavePort &port) const
	Convert a single port to a corresponding, one-hot bitmask. More...

SnoopList	maskToPortList (SnoopMask ports) const
	Converts a bitmask of ports into the corresponing list of ports. More...

Protected Member Functions inherited from Drainable
	Drainable ()

virtual	~Drainable ()

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

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

Private Types
enum	LineStatus { LineSecure = 0x01 }
	Use the lower bits of the address to keep track of the line status. More...

Private Member Functions
void	eraseIfNullEntry (SnoopFilterCache::iterator &sf_it)
	Removes snoop filter items which have no requesters and no holders. More...

Private Attributes
SnoopFilterCache	cachedLocations
	Simple hash set of cached addresses. More...

SnoopFilterCache::iterator	reqLookupResult
	Iterator used to store the result from lookupRequest until we call finishRequest. More...

SnoopItem	retryItem
	Variable to temporarily store value of snoopfilter entry incase finishRequest needs to undo changes made in lookupRequest (because of crossbar retry) More...

SnoopList	slavePorts
	List of all attached snooping slave ports. More...

std::vector< PortID >	localSlavePortIds
	Track the mapping from port ids to the local mask ids. More...

const unsigned	linesize
	Cache line size. More...

const Cycles	lookupLatency
	Latency for doing a lookup in the filter. More...

const unsigned	maxEntryCount
	Max capacity in terms of cache blocks tracked, for sanity checking. More...

Stats::Scalar	totRequests
	Statistics. More...

Stats::Scalar	hitSingleRequests

Stats::Scalar	hitMultiRequests

Stats::Scalar	totSnoops

Stats::Scalar	hitSingleSnoops

Stats::Scalar	hitMultiSnoops

Additional Inherited Members
Static Public Member Functions inherited from SimObject
static void	serializeAll (CheckpointOut &cp)
	Serialize all SimObjects in the system. More...

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

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

static void	serializeAll (const std::string &cpt_dir)

static void	unserializeGlobals (CheckpointIn &cp)

Static Public Attributes inherited from Serializable
static int	ckptCount = 0

static int	ckptMaxCount = 0

static int	ckptPrevCount = -1

Protected Attributes inherited from SimObject
const SimObjectParams *	_params
	Cached copy of the object parameters. More...

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

Detailed Description

This snoop filter keeps track of which connected port has a particular line of data.

It can be queried (through lookup*) on memory requests from above (reads / writes / ...); and also from below (snoops). The snoop filter precisely knows about the location of lines "above" it through a map from cache line address to sharers/ports. The snoop filter ties into the flows of requests (when they succeed at the lower interface), regular responses from below and also responses from sideway's caches (in update*). This allows the snoop filter to model cache-line residency by snooping the messages.

The tracking happens in two fields to be able to distinguish between in-flight requests (in requested) and already pulled in lines (in holder). This distinction is used for producing tighter assertions and tracking request completion. For safety, (requested | holder) should be notified and the requesting MSHRs will take care of ordering.

Overall, some trickery is required because: (1) snoops are not followed by an ACK, but only evoke a response if they need to (hit dirty) (2) side-channel information is funnelled through direct modifications of pkt, instead of proper messages through the bus (3) there are no clean evict messages telling the snoop filter that a local, upper cache dropped a line, making the snoop filter pessimistic for now (4) ordering: there is no single point of order in the system. Instead, requesting MSHRs track order between local requests and remote snoops

Definition at line 87 of file snoop_filter.hh.

Member Typedef Documentation

typedef std::unordered_map<Addr, SnoopItem> SnoopFilter::SnoopFilterCache

protected

HashMap of SnoopItems indexed by line address.

Definition at line 221 of file snoop_filter.hh.

typedef std::vector<QueuedSlavePort*> SnoopFilter::SnoopList

Definition at line 89 of file snoop_filter.hh.

typedef uint64_t SnoopFilter::SnoopMask

protected

The underlying type for the bitmask we use for tracking.

This limits the number of snooping ports supported per crossbar. For the moment it is an uint64_t to offer maximum scalability. However, it is possible to use e.g. a uint16_t or uint32_to slim down the footprint of the hash map (and ultimately improve the simulation performance).

Definition at line 207 of file snoop_filter.hh.

Member Enumeration Documentation

enum SnoopFilter::LineStatus

private

Use the lower bits of the address to keep track of the line status.

Enumerator
LineSecure	block holds data from the secure memory space

Definition at line 288 of file snoop_filter.hh.

Constructor & Destructor Documentation

SnoopFilter::SnoopFilter ( const SnoopFilterParams * p )

inline

Definition at line 91 of file snoop_filter.hh.

Member Function Documentation

void SnoopFilter::eraseIfNullEntry ( SnoopFilterCache::iterator & sf_it )

private

Removes snoop filter items which have no requesters and no holders.

Definition at line 53 of file snoop_filter.cc.

References cachedLocations, DPRINTF, SnoopFilter::SnoopItem::holder, and SnoopFilter::SnoopItem::requested.

Referenced by finishRequest(), lookupSnoop(), and updateSnoopForward().

void SnoopFilter::finishRequest	(	bool	will_retry,
		Addr	addr,
		bool	is_secure
	)

For an un-successful request, revert the change to the snoop filter.

Also take care of erasing any null entries. This method relies on the result from lookupRequest being stored in reqLookupResult.

Parameters

will_retry	This request will retry on this bus / snoop filter
addr	Packet address, merely for sanity checking

Definition at line 153 of file snoop_filter.cc.

References cachedLocations, DPRINTF, eraseIfNullEntry(), SnoopFilter::SnoopItem::holder, LineSecure, linesize, reqLookupResult, SnoopFilter::SnoopItem::requested, and retryItem.

Referenced by CoherentXBar::recvAtomic(), and CoherentXBar::recvTimingReq().

std::pair< SnoopFilter::SnoopList, Cycles > SnoopFilter::lookupRequest	(	const Packet *	cpkt,
		const SlavePort &	slave_port
	)

Lookup a request (from a slave port) in the snoop filter and return a list of other slave ports that need forwarding of the resulting snoops.

Additionally, update the tracking structures with new request information. Note that the caller must also call finishRequest once it is known if the request needs to retry or not.

Parameters

cpkt	Pointer to the request packet. Not changed.
slave_port	Slave port where the request came from.

Returns: Pair of a vector of snoop target ports and lookup latency.

Definition at line 64 of file snoop_filter.cc.

References cachedLocations, Packet::cacheResponding(), DPRINTF, Packet::fromCache(), Packet::getBlockAddr(), hitMultiRequests, hitSingleRequests, SnoopFilter::SnoopItem::holder, Packet::isBlockCached(), Packet::isEviction(), isPow2(), Packet::isSecure(), SlavePort::isSnooping(), Request::isUncacheable(), LineSecure, linesize, lookupLatency, maskToPortList(), Port::name(), Packet::needsResponse(), panic_if(), portToMask(), Packet::print(), Packet::req, reqLookupResult, SnoopFilter::SnoopItem::requested, retryItem, snoopDown(), snoopSelected(), and totRequests.

Referenced by CoherentXBar::recvAtomic(), and CoherentXBar::recvTimingReq().

std::pair< SnoopFilter::SnoopList, Cycles > SnoopFilter::lookupSnoop ( const Packet * cpkt )

Handle an incoming snoop from below (the master port).

These can upgrade the tracking logic and may also benefit from additional steering thanks to the snoop filter.

Parameters

cpkt	Pointer to const Packet containing the snoop.

Returns: Pair with a vector of SlavePorts that need snooping and a lookup latency.

Definition at line 178 of file snoop_filter.cc.

References cachedLocations, DPRINTF, eraseIfNullEntry(), Packet::getBlockAddr(), hitMultiSnoops, hitSingleSnoops, SnoopFilter::SnoopItem::holder, Packet::isInvalidate(), isPow2(), Packet::isRequest(), Packet::isSecure(), Request::isUncacheable(), Packet::isWriteback(), LineSecure, linesize, lookupLatency, maskToPortList(), maxEntryCount, Packet::needsWritable(), panic_if(), Packet::print(), Packet::req, SnoopFilter::SnoopItem::requested, snoopDown(), snoopSelected(), and totSnoops.

Referenced by CoherentXBar::recvAtomicSnoop(), and CoherentXBar::recvTimingSnoopReq().

SnoopFilter::SnoopList SnoopFilter::maskToPortList ( SnoopMask ports ) const

inlineprotected

Converts a bitmask of ports into the corresponing list of ports.

Parameters

ports SnoopMask of the requested ports

Returns: SnoopList containing all the requested SlavePorts

Definition at line 313 of file snoop_filter.hh.

References MipsISA::p, portToMask(), and slavePorts.

Referenced by lookupRequest(), and lookupSnoop().

SnoopFilter::SnoopMask SnoopFilter::portToMask ( const SlavePort & port ) const

inlineprotected

Convert a single port to a corresponding, one-hot bitmask.

Parameters

port	SlavePort that should be converted.

Returns: One-hot bitmask corresponding to the port.

Definition at line 304 of file snoop_filter.hh.

References Port::getId(), InvalidPortID, SlavePort::isSnooping(), and localSlavePortIds.

Referenced by lookupRequest(), maskToPortList(), updateResponse(), and updateSnoopResponse().

void SnoopFilter::regStats ( )

virtual

Register statistics for this object.

Reimplemented from SimObject.

Definition at line 371 of file snoop_filter.cc.

References Stats::DataWrap< Derived, InfoProxyType >::desc(), hitMultiRequests, hitMultiSnoops, hitSingleRequests, hitSingleSnoops, SimObject::name(), Stats::DataWrap< Derived, InfoProxyType >::name(), SimObject::regStats(), totRequests, and totSnoops.

void SnoopFilter::setSlavePorts ( const SnoopList & slave_ports )

inline

Init a new snoop filter and tell it about all the slave ports of the enclosing bus.

Parameters

slave_ports Slave ports that the bus is attached to.

Definition at line 104 of file snoop_filter.hh.

References fatal_if(), InvalidPortID, localSlavePortIds, MipsISA::p, and slavePorts.

Referenced by CoherentXBar::init().

std::pair<SnoopList, Cycles> SnoopFilter::snoopAll ( Cycles latency ) const

inlineprotected

Simple factory methods for standard return values.

Definition at line 226 of file snoop_filter.hh.

References slavePorts.

std::pair<SnoopList, Cycles> SnoopFilter::snoopDown ( Cycles latency ) const

inlineprotected

Definition at line 235 of file snoop_filter.hh.

Referenced by lookupRequest(), and lookupSnoop().

std::pair<SnoopList, Cycles> SnoopFilter::snoopSelected	(	const SnoopList &	slave_ports,
		Cycles	latency
	)		const

inlineprotected

Definition at line 230 of file snoop_filter.hh.

Referenced by lookupRequest(), and lookupSnoop().

void SnoopFilter::updateResponse	(	const Packet *	cpkt,
		const SlavePort &	slave_port
	)

Update the snoop filter with a response from below (outer / other cache, or memory) and update the tracking information in the snoop filter.

Parameters

cpkt	Pointer to const Packet holding the snoop response.
slave_port	SlavePort that made the original request and is the target of this response.

Definition at line 331 of file snoop_filter.cc.

References cachedLocations, DPRINTF, Packet::getBlockAddr(), SnoopFilter::SnoopItem::holder, Packet::isResponse(), Packet::isSecure(), SlavePort::isSnooping(), Request::isUncacheable(), LineSecure, linesize, Port::name(), panic_if(), portToMask(), Packet::print(), Packet::req, and SnoopFilter::SnoopItem::requested.

Referenced by CoherentXBar::recvAtomic(), CoherentXBar::recvTimingReq(), and CoherentXBar::recvTimingResp().

void SnoopFilter::updateSnoopForward	(	const Packet *	cpkt,
		const SlavePort &	rsp_port,
		const MasterPort &	req_port
	)

Pass snoop responses that travel downward through the snoop filter and let them update the snoop filter state.

No additional routing happens.

Parameters

cpkt	Pointer to const Packet holding the snoop response.
rsp_port	SlavePort that sends the response.
req_port	MasterPort through which the response is forwarded.

Definition at line 293 of file snoop_filter.cc.

References cachedLocations, Packet::cacheResponding(), DPRINTF, eraseIfNullEntry(), Packet::getBlockAddr(), Packet::hasSharers(), SnoopFilter::SnoopItem::holder, Packet::isResponse(), Packet::isSecure(), LineSecure, linesize, Port::name(), Packet::print(), and SnoopFilter::SnoopItem::requested.

Referenced by CoherentXBar::forwardAtomic(), and CoherentXBar::recvTimingSnoopResp().

void SnoopFilter::updateSnoopResponse	(	const Packet *	cpkt,
		const SlavePort &	rsp_port,
		const SlavePort &	req_port
	)

Let the snoop filter see any snoop responses that turn into request responses and indicate cache to cache transfers.

These will update the corresponding state in the filter.

Parameters

cpkt	Pointer to const Packet holding the snoop response.
rsp_port	SlavePort that sends the response.
req_port	SlavePort that made the original request and is the destination of the snoop response.

Definition at line 237 of file snoop_filter.cc.

References cachedLocations, Packet::cacheResponding(), DPRINTF, Packet::getBlockAddr(), Packet::hasSharers(), SnoopFilter::SnoopItem::holder, Packet::isResponse(), Packet::isSecure(), SlavePort::isSnooping(), Request::isUncacheable(), Packet::isWriteback(), LineSecure, linesize, Port::name(), panic_if(), portToMask(), Packet::print(), Packet::req, and SnoopFilter::SnoopItem::requested.