gem5  v21.1.0.2
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gem5::SnoopFilter Class Reference

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

#include <snoop_filter.hh>

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

Classes

struct  ReqLookupResult
 A request lookup must be followed by a call to finishRequest to inform the operation's success. More...
 
struct  SnoopFilterStats
 Statistics. More...
 
struct  SnoopItem
 Per cache line item tracking a bitmask of ResponsePorts 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< QueuedResponsePort * > SnoopList
 
- Public Types inherited from gem5::SimObject
typedef SimObjectParams Params
 

Public Member Functions

 SnoopFilter (const SnoopFilterParams &p)
 
void setCPUSidePorts (const SnoopList &_cpu_side_ports)
 Init a new snoop filter and tell it about all the cpu_sideports of the enclosing bus. More...
 
std::pair< SnoopList, CycleslookupRequest (const Packet *cpkt, const ResponsePort &cpu_side_port)
 Lookup a request (from a CPU-side port) in the snoop filter and return a list of other CPU-side 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, CycleslookupSnoop (const Packet *cpkt)
 Handle an incoming snoop from below (the memory-side port). More...
 
void updateSnoopResponse (const Packet *cpkt, const ResponsePort &rsp_port, const ResponsePort &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 ResponsePort &rsp_port, const RequestPort &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 ResponsePort &cpu_side_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 ()
 Callback to set stat parameters. 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 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
 

Static Public Attributes

static const int SNOOP_MASK_SIZE = 256
 

Protected Types

typedef std::bitset< SNOOP_MASK_SIZESnoopMask
 The underlying type for the bitmask we use for tracking. More...
 
typedef std::unordered_map< Addr, SnoopItemSnoopFilterCache
 HashMap of SnoopItems indexed by line address. More...
 

Protected Member Functions

std::pair< SnoopList, CyclessnoopAll (Cycles latency) const
 Simple factory methods for standard return values. More...
 
std::pair< SnoopList, CyclessnoopSelected (const SnoopList &_cpu_side_ports, Cycles latency) const
 
std::pair< SnoopList, CyclessnoopDown (Cycles latency) const
 
SnoopMask portToMask (const ResponsePort &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 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...
 

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 requestors and no holders. More...
 

Private Attributes

SnoopFilterCache cachedLocations
 Simple hash set of cached addresses. More...
 
struct gem5::SnoopFilter::ReqLookupResult reqLookupResult
 
SnoopList cpuSidePorts
 List of all attached snooping CPU-side ports. More...
 
std::vector< PortIDlocalResponsePortIds
 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...
 
gem5::SnoopFilter::SnoopFilterStats stats
 

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 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

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 89 of file snoop_filter.hh.

Member Typedef Documentation

◆ SnoopFilterCache

typedef std::unordered_map<Addr, SnoopItem> gem5::SnoopFilter::SnoopFilterCache
protected

HashMap of SnoopItems indexed by line address.

Definition at line 226 of file snoop_filter.hh.

◆ SnoopList

Definition at line 96 of file snoop_filter.hh.

◆ SnoopMask

typedef std::bitset<SNOOP_MASK_SIZE> gem5::SnoopFilter::SnoopMask
protected

The underlying type for the bitmask we use for tracking.

This limits the number of snooping ports supported per crossbar.

Definition at line 211 of file snoop_filter.hh.

Member Enumeration Documentation

◆ LineStatus

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 314 of file snoop_filter.hh.

Constructor & Destructor Documentation

◆ SnoopFilter()

gem5::SnoopFilter::SnoopFilter ( const SnoopFilterParams &  p)
inline

Definition at line 98 of file snoop_filter.hh.

Member Function Documentation

◆ eraseIfNullEntry()

void gem5::SnoopFilter::eraseIfNullEntry ( SnoopFilterCache::iterator &  sf_it)
private

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

Definition at line 56 of file snoop_filter.cc.

References cachedLocations, DPRINTF, gem5::SnoopFilter::SnoopItem::holder, and gem5::SnoopFilter::SnoopItem::requested.

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

◆ finishRequest()

void gem5::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_retryThis request will retry on this bus / snoop filter
addrPacket address, merely for sanity checking

Definition at line 160 of file snoop_filter.cc.

References gem5::X86ISA::addr, cachedLocations, DPRINTF, eraseIfNullEntry(), gem5::SnoopFilter::SnoopItem::holder, gem5::SnoopFilter::ReqLookupResult::it, LineSecure, linesize, reqLookupResult, gem5::SnoopFilter::SnoopItem::requested, and gem5::SnoopFilter::ReqLookupResult::retryItem.

Referenced by gem5::CoherentXBar::recvAtomicBackdoor(), and gem5::CoherentXBar::recvTimingReq().

◆ lookupRequest()

std::pair< SnoopFilter::SnoopList, Cycles > gem5::SnoopFilter::lookupRequest ( const Packet cpkt,
const ResponsePort cpu_side_port 
)

Lookup a request (from a CPU-side port) in the snoop filter and return a list of other CPU-side 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
cpktPointer to the request packet. Not changed.
cpu_side_portResponse port where the request came from.
Returns
Pair of a vector of snoop target ports and lookup latency.

Definition at line 67 of file snoop_filter.cc.

References cachedLocations, gem5::Packet::cacheResponding(), DPRINTF, gem5::Packet::fromCache(), gem5::Packet::getBlockAddr(), gem5::SnoopFilter::SnoopFilterStats::hitMultiRequests, gem5::SnoopFilter::SnoopFilterStats::hitSingleRequests, gem5::SnoopFilter::SnoopItem::holder, gem5::Packet::isBlockCached(), gem5::Packet::isEviction(), gem5::Packet::isSecure(), gem5::ResponsePort::isSnooping(), gem5::SnoopFilter::ReqLookupResult::it, LineSecure, linesize, lookupLatency, maskToPortList(), gem5::Port::name(), gem5::Packet::needsResponse(), panic_if, portToMask(), gem5::Packet::print(), gem5::Packet::req, reqLookupResult, gem5::SnoopFilter::SnoopItem::requested, gem5::SnoopFilter::ReqLookupResult::retryItem, snoopDown(), snoopSelected(), stats, and gem5::SnoopFilter::SnoopFilterStats::totRequests.

Referenced by gem5::CoherentXBar::recvAtomicBackdoor(), and gem5::CoherentXBar::recvTimingReq().

◆ lookupSnoop()

std::pair< SnoopFilter::SnoopList, Cycles > gem5::SnoopFilter::lookupSnoop ( const Packet cpkt)

◆ maskToPortList()

SnoopFilter::SnoopList gem5::SnoopFilter::maskToPortList ( SnoopMask  ports) const
inlineprotected

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

Parameters
portsSnoopMask of the requested ports
Returns
SnoopList containing all the requested ResponsePorts

Definition at line 345 of file snoop_filter.hh.

References cpuSidePorts, gem5::MipsISA::p, and portToMask().

Referenced by lookupRequest(), and lookupSnoop().

◆ portToMask()

SnoopFilter::SnoopMask gem5::SnoopFilter::portToMask ( const ResponsePort port) const
inlineprotected

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

Parameters
portResponsePort that should be converted.
Returns
One-hot bitmask corresponding to the port.

Definition at line 336 of file snoop_filter.hh.

References gem5::Port::getId(), gem5::InvalidPortID, gem5::ResponsePort::isSnooping(), and localResponsePortIds.

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

◆ regStats()

void gem5::SnoopFilter::regStats ( )
virtual

Callback to set stat parameters.

This callback is typically used for complex stats (e.g., distributions) that need parameters in addition to a name and a description. Stat names and descriptions should typically be set from the constructor usingo from the constructor using the ADD_STAT macro.

Reimplemented from gem5::statistics::Group.

Definition at line 414 of file snoop_filter.cc.

References gem5::statistics::Group::regStats().

◆ setCPUSidePorts()

void gem5::SnoopFilter::setCPUSidePorts ( const SnoopList _cpu_side_ports)
inline

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

Parameters
_cpu_side_portsResponse ports that the bus is attached to.

Definition at line 112 of file snoop_filter.hh.

References cpuSidePorts, fatal_if, gem5::InvalidPortID, localResponsePortIds, gem5::MipsISA::p, and SNOOP_MASK_SIZE.

Referenced by gem5::CoherentXBar::init().

◆ snoopAll()

std::pair<SnoopList, Cycles> gem5::SnoopFilter::snoopAll ( Cycles  latency) const
inlineprotected

Simple factory methods for standard return values.

Definition at line 231 of file snoop_filter.hh.

References cpuSidePorts.

◆ snoopDown()

std::pair<SnoopList, Cycles> gem5::SnoopFilter::snoopDown ( Cycles  latency) const
inlineprotected

Definition at line 240 of file snoop_filter.hh.

Referenced by lookupRequest(), and lookupSnoop().

◆ snoopSelected()

std::pair<SnoopList, Cycles> gem5::SnoopFilter::snoopSelected ( const SnoopList _cpu_side_ports,
Cycles  latency 
) const
inlineprotected

Definition at line 235 of file snoop_filter.hh.

Referenced by lookupRequest(), and lookupSnoop().

◆ updateResponse()

void gem5::SnoopFilter::updateResponse ( const Packet cpkt,
const ResponsePort cpu_side_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
cpktPointer to const Packet holding the snoop response.
cpu_side_portResponsePort that made the original request and is the target of this response.

Definition at line 340 of file snoop_filter.cc.

References cachedLocations, DPRINTF, eraseIfNullEntry(), gem5::Packet::getBlockAddr(), gem5::SnoopFilter::SnoopItem::holder, gem5::Packet::isInvalidate(), gem5::Packet::isResponse(), gem5::Packet::isSecure(), gem5::ResponsePort::isSnooping(), LineSecure, linesize, gem5::Port::name(), panic_if, portToMask(), gem5::Packet::print(), gem5::Packet::req, and gem5::SnoopFilter::SnoopItem::requested.

Referenced by gem5::CoherentXBar::recvAtomicBackdoor(), gem5::CoherentXBar::recvTimingReq(), and gem5::CoherentXBar::recvTimingResp().

◆ updateSnoopForward()

void gem5::SnoopFilter::updateSnoopForward ( const Packet cpkt,
const ResponsePort rsp_port,
const RequestPort 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
cpktPointer to const Packet holding the snoop response.
rsp_portResponsePort that sends the response.
req_portRequestPort through which the response is forwarded.

Definition at line 303 of file snoop_filter.cc.

References cachedLocations, gem5::Packet::cacheResponding(), DPRINTF, eraseIfNullEntry(), gem5::Packet::getBlockAddr(), gem5::Packet::hasSharers(), gem5::SnoopFilter::SnoopItem::holder, gem5::Packet::isResponse(), gem5::Packet::isSecure(), LineSecure, linesize, gem5::Port::name(), gem5::Packet::print(), and gem5::SnoopFilter::SnoopItem::requested.

Referenced by gem5::CoherentXBar::forwardAtomic(), and gem5::CoherentXBar::recvTimingSnoopResp().

◆ updateSnoopResponse()

void gem5::SnoopFilter::updateSnoopResponse ( const Packet cpkt,
const ResponsePort rsp_port,
const ResponsePort 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
cpktPointer to const Packet holding the snoop response.
rsp_portResponsePort that sends the response.
req_portResponsePort that made the original request and is the destination of the snoop response.

Definition at line 246 of file snoop_filter.cc.

References cachedLocations, gem5::Packet::cacheResponding(), DPRINTF, gem5::Packet::getBlockAddr(), gem5::Packet::hasSharers(), gem5::SnoopFilter::SnoopItem::holder, gem5::Packet::isResponse(), gem5::Packet::isSecure(), gem5::ResponsePort::isSnooping(), gem5::Packet::isWriteback(), LineSecure, linesize, gem5::Port::name(), panic_if, portToMask(), gem5::Packet::print(), gem5::Packet::req, and gem5::SnoopFilter::SnoopItem::requested.

Referenced by gem5::CoherentXBar::forwardAtomic(), and gem5::CoherentXBar::recvTimingSnoopResp().

Member Data Documentation

◆ cachedLocations

SnoopFilterCache gem5::SnoopFilter::cachedLocations
private

Simple hash set of cached addresses.

Definition at line 267 of file snoop_filter.hh.

Referenced by eraseIfNullEntry(), finishRequest(), lookupRequest(), lookupSnoop(), updateResponse(), updateSnoopForward(), and updateSnoopResponse().

◆ cpuSidePorts

SnoopList gem5::SnoopFilter::cpuSidePorts
private

List of all attached snooping CPU-side ports.

Definition at line 301 of file snoop_filter.hh.

Referenced by maskToPortList(), setCPUSidePorts(), and snoopAll().

◆ linesize

const unsigned gem5::SnoopFilter::linesize
private

◆ localResponsePortIds

std::vector<PortID> gem5::SnoopFilter::localResponsePortIds
private

Track the mapping from port ids to the local mask ids.

Definition at line 303 of file snoop_filter.hh.

Referenced by portToMask(), and setCPUSidePorts().

◆ lookupLatency

const Cycles gem5::SnoopFilter::lookupLatency
private

Latency for doing a lookup in the filter.

Definition at line 307 of file snoop_filter.hh.

Referenced by lookupRequest(), and lookupSnoop().

◆ maxEntryCount

const unsigned gem5::SnoopFilter::maxEntryCount
private

Max capacity in terms of cache blocks tracked, for sanity checking.

Definition at line 309 of file snoop_filter.hh.

Referenced by lookupSnoop().

◆ reqLookupResult

struct gem5::SnoopFilter::ReqLookupResult gem5::SnoopFilter::reqLookupResult
private

Referenced by finishRequest(), and lookupRequest().

◆ SNOOP_MASK_SIZE

const int gem5::SnoopFilter::SNOOP_MASK_SIZE = 256
static

Definition at line 94 of file snoop_filter.hh.

Referenced by setCPUSidePorts().

◆ stats

gem5::SnoopFilter::SnoopFilterStats gem5::SnoopFilter::stats
private

Referenced by lookupRequest(), and lookupSnoop().


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

Generated on Tue Sep 21 2021 12:28:11 for gem5 by doxygen 1.8.17