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/*
* Copyright (c) 2013-2016 ARM Limited
* All rights reserved
*
* The license below extends only to copyright in the software and shall
* not be construed as granting a license to any other intellectual
* property including but not limited to intellectual property relating
* to a hardware implementation of the functionality of the software
* licensed hereunder. You may use the software subject to the license
* terms below provided that you ensure that this notice is replicated
* unmodified and in its entirety in all distributions of the software,
* modified or unmodified, in source code or in binary form.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
* redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution;
* neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* Authors: Stephan Diestelhorst
*/
/**
* @file
* Definition of a snoop filter.
*/
#ifndef __MEM_SNOOP_FILTER_HH__
#define __MEM_SNOOP_FILTER_HH__
#include <unordered_map>
#include <utility>
#include "mem/packet.hh"
#include "mem/port.hh"
#include "mem/qport.hh"
#include "params/SnoopFilter.hh"
#include "sim/sim_object.hh"
#include "sim/system.hh"
/**
* 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
*/
class SnoopFilter : public SimObject {
public:
typedef std::vector<QueuedSlavePort*> SnoopList;
SnoopFilter (const SnoopFilterParams *p) :
SimObject(p), reqLookupResult(cachedLocations.end()), retryItem{0, 0},
linesize(p->system->cacheLineSize()), lookupLatency(p->lookup_latency),
maxEntryCount(p->max_capacity / p->system->cacheLineSize())
{
}
/**
* Init a new snoop filter and tell it about all the slave ports
* of the enclosing bus.
*
* @param slave_ports Slave ports that the bus is attached to.
*/
void setSlavePorts(const SnoopList& slave_ports) {
localSlavePortIds.resize(slave_ports.size(), InvalidPortID);
PortID id = 0;
for (const auto& p : slave_ports) {
// no need to track this port if it is not snooping
if (p->isSnooping()) {
slavePorts.push_back(p);
localSlavePortIds[p->getId()] = id++;
}
}
// make sure we can deal with this many ports
fatal_if(id > 8 * sizeof(SnoopMask),
"Snoop filter only supports %d snooping ports, got %d\n",
8 * sizeof(SnoopMask), id);
}
/**
* 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.
*
* @param cpkt Pointer to the request packet. Not changed.
* @param slave_port Slave port where the request came from.
* @return Pair of a vector of snoop target ports and lookup latency.
*/
std::pair<SnoopList, Cycles> lookupRequest(const Packet* cpkt,
const SlavePort& slave_port);
/**
* 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.
*
* @param will_retry This request will retry on this bus / snoop filter
* @param addr Packet address, merely for sanity checking
*/
void finishRequest(bool will_retry, Addr addr, bool is_secure);
/**
* 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.
*
* @param cpkt Pointer to const Packet containing the snoop.
* @return Pair with a vector of SlavePorts that need snooping and a lookup
* latency.
*/
std::pair<SnoopList, Cycles> lookupSnoop(const Packet* cpkt);
/**
* 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.
*
* @param cpkt Pointer to const Packet holding the snoop response.
* @param rsp_port SlavePort that sends the response.
* @param req_port SlavePort that made the original request and is the
* destination of the snoop response.
*/
void updateSnoopResponse(const Packet *cpkt, const SlavePort& rsp_port,
const SlavePort& req_port);
/**
* Pass snoop responses that travel downward through the snoop
* filter and let them update the snoop filter state. No
* additional routing happens.
*
* @param cpkt Pointer to const Packet holding the snoop response.
* @param rsp_port SlavePort that sends the response.
* @param req_port MasterPort through which the response is forwarded.
*/
void updateSnoopForward(const Packet *cpkt, const SlavePort& rsp_port,
const MasterPort& req_port);
/**
* Update the snoop filter with a response from below (outer /
* other cache, or memory) and update the tracking information in
* the snoop filter.
*
* @param cpkt Pointer to const Packet holding the snoop response.
* @param slave_port SlavePort that made the original request and
* is the target of this response.
*/
void updateResponse(const Packet *cpkt, const SlavePort& slave_port);
virtual void regStats();
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).
*/
typedef uint64_t SnoopMask;
/**
* 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).
*/
struct SnoopItem {
SnoopMask requested;
SnoopMask holder;
};
/**
* HashMap of SnoopItems indexed by line address
*/
typedef std::unordered_map<Addr, SnoopItem> SnoopFilterCache;
/**
* Simple factory methods for standard return values.
*/
std::pair<SnoopList, Cycles> snoopAll(Cycles latency) const
{
return std::make_pair(slavePorts, latency);
}
std::pair<SnoopList, Cycles> snoopSelected(const SnoopList& slave_ports,
Cycles latency) const
{
return std::make_pair(slave_ports, latency);
}
std::pair<SnoopList, Cycles> snoopDown(Cycles latency) const
{
SnoopList empty;
return std::make_pair(empty , latency);
}
/**
* Convert a single port to a corresponding, one-hot bitmask
* @param port SlavePort that should be converted.
* @return One-hot bitmask corresponding to the port.
*/
SnoopMask portToMask(const SlavePort& port) const;
/**
* Converts a bitmask of ports into the corresponing list of ports
* @param ports SnoopMask of the requested ports
* @return SnoopList containing all the requested SlavePorts
*/
SnoopList maskToPortList(SnoopMask ports) const;
private:
/**
* Removes snoop filter items which have no requesters and no holders.
*/
void eraseIfNullEntry(SnoopFilterCache::iterator& sf_it);
/** Simple hash set of cached addresses. */
SnoopFilterCache cachedLocations;
/**
* Iterator used to store the result from lookupRequest until we
* call finishRequest.
*/
SnoopFilterCache::iterator reqLookupResult;
/**
* Variable to temporarily store value of snoopfilter entry
* incase finishRequest needs to undo changes made in lookupRequest
* (because of crossbar retry)
*/
SnoopItem retryItem;
/** List of all attached snooping slave ports. */
SnoopList slavePorts;
/** Track the mapping from port ids to the local mask ids. */
std::vector<PortID> localSlavePortIds;
/** Cache line size. */
const unsigned linesize;
/** Latency for doing a lookup in the filter */
const Cycles lookupLatency;
/** Max capacity in terms of cache blocks tracked, for sanity checking */
const unsigned maxEntryCount;
/**
* Use the lower bits of the address to keep track of the line status
*/
enum LineStatus {
/** block holds data from the secure memory space */
LineSecure = 0x01,
};
/** Statistics */
Stats::Scalar totRequests;
Stats::Scalar hitSingleRequests;
Stats::Scalar hitMultiRequests;
Stats::Scalar totSnoops;
Stats::Scalar hitSingleSnoops;
Stats::Scalar hitMultiSnoops;
};
inline SnoopFilter::SnoopMask
SnoopFilter::portToMask(const SlavePort& port) const
{
assert(port.getId() != InvalidPortID);
// if this is not a snooping port, return a zero mask
return !port.isSnooping() ? 0 :
((SnoopMask)1) << localSlavePortIds[port.getId()];
}
inline SnoopFilter::SnoopList
SnoopFilter::maskToPortList(SnoopMask port_mask) const
{
SnoopList res;
for (const auto& p : slavePorts)
if (port_mask & portToMask(*p))
res.push_back(p);
return res;
}
#endif // __MEM_SNOOP_FILTER_HH__