gem5
v20.1.0.0
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This snoop filter keeps track of which connected port has a particular line of data. More...
#include <snoop_filter.hh>
Classes | |
struct | ReqLookupResult |
A request lookup must be followed by a call to finishRequest to inform the operation's success. 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 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, Cycles > | 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. 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 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 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 | 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 Port & | getPort (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 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. 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 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... | |
Public Member Functions inherited from Stats::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 (Stats::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 Info * | resolveStat (std::string name) const |
Resolve a stat by its name within this group. More... | |
Group ()=delete | |
Group (const Group &)=delete | |
Group & | operator= (const Group &)=delete |
Static Public Attributes | |
static const int | SNOOP_MASK_SIZE = 256 |
Protected Types | |
typedef std::bitset< SNOOP_MASK_SIZE > | 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 &_cpu_side_ports, Cycles latency) const |
std::pair< SnoopList, Cycles > | snoopDown (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 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 SnoopFilter::ReqLookupResult | reqLookupResult |
SnoopList | cpuSidePorts |
List of all attached snooping CPU-side ports. More... | |
std::vector< PortID > | localResponsePortIds |
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 () |
Gets the fully-qualified name of the active section. More... | |
static void | serializeAll (const std::string &cpt_dir) |
Serializes all the SimObjects. More... | |
static void | unserializeGlobals (CheckpointIn &cp) |
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... | |
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 86 of file snoop_filter.hh.
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HashMap of SnoopItems indexed by line address.
Definition at line 220 of file snoop_filter.hh.
Definition at line 92 of file snoop_filter.hh.
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The underlying type for the bitmask we use for tracking.
This limits the number of snooping ports supported per crossbar.
Definition at line 206 of file snoop_filter.hh.
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Use the lower bits of the address to keep track of the line status.
Enumerator | |
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LineSecure | block holds data from the secure memory space |
Definition at line 307 of file snoop_filter.hh.
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Definition at line 94 of file snoop_filter.hh.
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Removes snoop filter items which have no requestors 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(), updateResponse(), 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.
will_retry | This request will retry on this bus / snoop filter |
addr | Packet address, merely for sanity checking |
Definition at line 157 of file snoop_filter.cc.
References addr, cachedLocations, DPRINTF, eraseIfNullEntry(), SnoopFilter::SnoopItem::holder, SnoopFilter::ReqLookupResult::it, LineSecure, linesize, reqLookupResult, SnoopFilter::SnoopItem::requested, and SnoopFilter::ReqLookupResult::retryItem.
Referenced by CoherentXBar::recvAtomicBackdoor(), and CoherentXBar::recvTimingReq().
std::pair< SnoopFilter::SnoopList, Cycles > 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.
cpkt | Pointer to the request packet. Not changed. |
cpu_side_port | Response port where the request came from. |
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(), Packet::isSecure(), ResponsePort::isSnooping(), SnoopFilter::ReqLookupResult::it, LineSecure, linesize, lookupLatency, maskToPortList(), Port::name(), Packet::needsResponse(), panic_if, portToMask(), Packet::print(), Packet::req, reqLookupResult, SnoopFilter::SnoopItem::requested, SnoopFilter::ReqLookupResult::retryItem, snoopDown(), snoopSelected(), and totRequests.
Referenced by CoherentXBar::recvAtomicBackdoor(), and CoherentXBar::recvTimingReq().
std::pair< SnoopFilter::SnoopList, Cycles > SnoopFilter::lookupSnoop | ( | const Packet * | cpkt | ) |
Handle an incoming snoop from below (the memory-side port).
These can upgrade the tracking logic and may also benefit from additional steering thanks to the snoop filter.
cpkt | Pointer to const Packet containing the snoop. |
Definition at line 183 of file snoop_filter.cc.
References cachedLocations, DPRINTF, eraseIfNullEntry(), Packet::getBlockAddr(), hitMultiSnoops, hitSingleSnoops, SnoopFilter::SnoopItem::holder, Packet::isInvalidate(), Packet::isRequest(), Packet::isSecure(), 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().
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Converts a bitmask of ports into the corresponing list of ports.
ports | SnoopMask of the requested ports |
Definition at line 332 of file snoop_filter.hh.
References cpuSidePorts, MipsISA::p, and portToMask().
Referenced by lookupRequest(), and lookupSnoop().
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Convert a single port to a corresponding, one-hot bitmask.
port | ResponsePort that should be converted. |
Definition at line 323 of file snoop_filter.hh.
References Port::getId(), InvalidPortID, ResponsePort::isSnooping(), and localResponsePortIds.
Referenced by lookupRequest(), maskToPortList(), updateResponse(), and updateSnoopResponse().
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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 Stats::Group.
Definition at line 391 of file snoop_filter.cc.
References Stats::DataWrap< Derived, InfoProxyType >::desc(), hitMultiRequests, hitMultiSnoops, hitSingleRequests, hitSingleSnoops, SimObject::name(), Stats::DataWrap< Derived, InfoProxyType >::name(), Stats::Group::regStats(), totRequests, and totSnoops.
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Init a new snoop filter and tell it about all the cpu_sideports of the enclosing bus.
_cpu_side_ports | Response ports that the bus is attached to. |
Definition at line 107 of file snoop_filter.hh.
References cpuSidePorts, fatal_if, InvalidPortID, localResponsePortIds, MipsISA::p, and SNOOP_MASK_SIZE.
Referenced by CoherentXBar::init().
Simple factory methods for standard return values.
Definition at line 225 of file snoop_filter.hh.
References cpuSidePorts.
Definition at line 234 of file snoop_filter.hh.
Referenced by lookupRequest(), and lookupSnoop().
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Definition at line 229 of file snoop_filter.hh.
Referenced by lookupRequest(), and lookupSnoop().
void 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.
cpkt | Pointer to const Packet holding the snoop response. |
cpu_side_port | ResponsePort that made the original request and is the target of this response. |
Definition at line 337 of file snoop_filter.cc.
References cachedLocations, DPRINTF, eraseIfNullEntry(), Packet::getBlockAddr(), SnoopFilter::SnoopItem::holder, Packet::isInvalidate(), Packet::isResponse(), Packet::isSecure(), ResponsePort::isSnooping(), LineSecure, linesize, Port::name(), panic_if, portToMask(), Packet::print(), Packet::req, and SnoopFilter::SnoopItem::requested.
Referenced by CoherentXBar::recvAtomicBackdoor(), CoherentXBar::recvTimingReq(), and CoherentXBar::recvTimingResp().
void 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.
cpkt | Pointer to const Packet holding the snoop response. |
rsp_port | ResponsePort that sends the response. |
req_port | RequestPort through which the response is forwarded. |
Definition at line 300 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 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.
cpkt | Pointer to const Packet holding the snoop response. |
rsp_port | ResponsePort that sends the response. |
req_port | ResponsePort that made the original request and is the destination of the snoop response. |
Definition at line 243 of file snoop_filter.cc.
References cachedLocations, Packet::cacheResponding(), DPRINTF, Packet::getBlockAddr(), Packet::hasSharers(), SnoopFilter::SnoopItem::holder, Packet::isResponse(), Packet::isSecure(), ResponsePort::isSnooping(), Packet::isWriteback(), LineSecure, linesize, Port::name(), panic_if, portToMask(), Packet::print(), Packet::req, and SnoopFilter::SnoopItem::requested.
Referenced by CoherentXBar::forwardAtomic(), and CoherentXBar::recvTimingSnoopResp().
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Simple hash set of cached addresses.
Definition at line 261 of file snoop_filter.hh.
Referenced by eraseIfNullEntry(), finishRequest(), lookupRequest(), lookupSnoop(), updateResponse(), updateSnoopForward(), and updateSnoopResponse().
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List of all attached snooping CPU-side ports.
Definition at line 294 of file snoop_filter.hh.
Referenced by maskToPortList(), setCPUSidePorts(), and snoopAll().
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Definition at line 315 of file snoop_filter.hh.
Referenced by lookupRequest(), and regStats().
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Definition at line 319 of file snoop_filter.hh.
Referenced by lookupSnoop(), and regStats().
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Definition at line 314 of file snoop_filter.hh.
Referenced by lookupRequest(), and regStats().
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Definition at line 318 of file snoop_filter.hh.
Referenced by lookupSnoop(), and regStats().
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Cache line size.
Definition at line 298 of file snoop_filter.hh.
Referenced by finishRequest(), lookupRequest(), lookupSnoop(), updateResponse(), updateSnoopForward(), and updateSnoopResponse().
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Track the mapping from port ids to the local mask ids.
Definition at line 296 of file snoop_filter.hh.
Referenced by portToMask(), and setCPUSidePorts().
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Latency for doing a lookup in the filter.
Definition at line 300 of file snoop_filter.hh.
Referenced by lookupRequest(), and lookupSnoop().
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Max capacity in terms of cache blocks tracked, for sanity checking.
Definition at line 302 of file snoop_filter.hh.
Referenced by lookupSnoop().
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Referenced by finishRequest(), and lookupRequest().
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Definition at line 90 of file snoop_filter.hh.
Referenced by setCPUSidePorts().
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Statistics.
Definition at line 313 of file snoop_filter.hh.
Referenced by lookupRequest(), and regStats().
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Definition at line 317 of file snoop_filter.hh.
Referenced by lookupSnoop(), and regStats().