mem: Simple Snoop Filter

This is a first cut at a simple snoop filter that tracks presence of lines in
the caches "above" it. The snoop filter can be applied at any given cache
hierarchy and will then handle the caches above it appropriately; there is no
need to use this only in the last-level bus.

This design currently has some limitations: missing stats, no notion of clean
evictions (these will not update the underlying snoop filter, because they are
not sent from the evicting cache down), no notion of capacity for the snoop
filter and thus no need for invalidations caused by capacity pressure in the
snoop filter. These are planned to be added on top with future change sets.

4 files changed, 545 insertions, 1 deletions

diff --git a/src/mem/Bus.py b/src/mem/Bus.py
index e8e03ccb4..34d9ae664 100644
--- a/src/mem/Bus.py
+++ b/src/mem/Bus.py
@@ -43,6 +43,7 @@ from MemObject import MemObject
 from System import System
 from m5.params import *
 from m5.proxy import *
+from m5.SimObject import SimObject
 
 class BaseBus(MemObject):
     type = 'BaseBus'
@@ -74,3 +75,10 @@ class CoherentBus(BaseBus):
     cxx_header = "mem/coherent_bus.hh"
 
     system = Param.System(Parent.any, "System that the bus belongs to.")
+
+class SnoopFilter(SimObject):
+    type = 'SnoopFilter'
+    cxx_header = "mem/snoop_filter.hh"
+    lookup_latency = Param.Cycles(3, "lookup latency (cycles)")
+
+    system = Param.System(Parent.any, "System that the bus belongs to.")
diff --git a/src/mem/SConscript b/src/mem/SConscript
index dd96879e6..c351661b8 100644
--- a/src/mem/SConscript
+++ b/src/mem/SConscript
@@ -60,6 +60,7 @@ Source('tport.cc')
 Source('port_proxy.cc')
 Source('simple_mem.cc')
 Source('physical.cc')
+Source('snoop_filter.cc')
 
 if env['TARGET_ISA'] != 'null':
     Source('fs_translating_port_proxy.cc')
@@ -77,8 +78,9 @@ DebugFlag('BaseBus')
 DebugFlag('BusAddrRanges')
 DebugFlag('CoherentBus')
 DebugFlag('NoncoherentBus')
+DebugFlag('SnoopFilter')
 CompoundFlag('Bus', ['BaseBus', 'BusAddrRanges', 'CoherentBus',
-                     'NoncoherentBus'])
+                     'NoncoherentBus', 'SnoopFilter'])
 
 DebugFlag('Bridge')
 DebugFlag('CommMonitor')
diff --git a/src/mem/snoop_filter.cc b/src/mem/snoop_filter.cc
new file mode 100755
index 000000000..1acfbef6c
--- /dev/null
+++ b/src/mem/snoop_filter.cc
@@ -0,0 +1,274 @@
+/*
+ * Copyright (c) 2013 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 <stephan.diestelhorst@arm.com>
+ */
+
+/**
+ * @file
+ * Definition of a snoop filter.
+ */
+
+#include "base/misc.hh"
+#include "base/trace.hh"
+#include "debug/SnoopFilter.hh"
+#include "mem/snoop_filter.hh"
+#include "sim/system.hh"
+
+std::pair<SnoopFilter::SnoopList, Cycles>
+SnoopFilter::lookupRequest(const Packet* cpkt, const SlavePort& slave_port)
+{
+    DPRINTF(SnoopFilter, "%s: packet src %s addr 0x%x cmd %s\n",
+            __func__, slave_port.name(), cpkt->getAddr(), cpkt->cmdString());
+
+    Addr line_addr = cpkt->getAddr() & ~(linesize - 1);
+    SnoopMask req_port = portToMask(slave_port);
+    SnoopItem& sf_item  = cachedLocations[line_addr];
+
+    DPRINTF(SnoopFilter, "%s:   SF value %x.%x\n",
+            __func__, sf_item.requested, sf_item.holder);
+
+    if (cpkt->needsResponse()) {
+        if (!cpkt->memInhibitAsserted()) {
+            // Max one request per address per port
+            panic_if(sf_item.requested & req_port, "double request :( "\
+                     "SF value %x.%x\n", sf_item.requested, sf_item.holder);
+
+            // Mark in-flight requests to distinguish later on
+            sf_item.requested |= req_port;
+        } else {
+            // NOTE: The memInhibit might have been asserted by a cache closer
+            // to the CPU, already -> the response will not be seen by this
+            // filter -> we do not need to keep the in-flight request, but make
+            // sure that we know that that cluster has a copy
+            panic_if(!(sf_item.holder & req_port), "Need to hold the value!");
+            DPRINTF(SnoopFilter, "%s:   not marking request. SF value %x.%x\n",
+                    __func__,  sf_item.requested, sf_item.holder);
+        }
+        DPRINTF(SnoopFilter, "%s:   new SF value %x.%x\n",
+                __func__,  sf_item.requested, sf_item.holder);
+    }
+    SnoopMask interested = (sf_item.holder | sf_item.requested) & ~req_port;
+    return snoopSelected(maskToPortList(interested), lookupLatency);
+}
+
+void
+SnoopFilter::updateRequest(const Packet* cpkt, const SlavePort& slave_port,
+                           bool will_retry)
+{
+    DPRINTF(SnoopFilter, "%s: packet src %s addr 0x%x cmd %s\n",
+            __func__, slave_port.name(), cpkt->getAddr(), cpkt->cmdString());
+
+    Addr line_addr = cpkt->getAddr() & ~(linesize - 1);
+    SnoopMask req_port = portToMask(slave_port);
+    SnoopItem& sf_item  = cachedLocations[line_addr];
+
+    DPRINTF(SnoopFilter, "%s:   old SF value %x.%x retry: %i\n",
+            __func__, sf_item.requested, sf_item.holder, will_retry);
+
+    if (will_retry) {
+        // Unmark a request that will come again.
+        sf_item.requested &= ~req_port;
+        return;
+    }
+
+    // will_retry == false
+    if (!cpkt->needsResponse()) {
+        // Packets that will not evoke a response but still need updates of the
+        // snoop filter; WRITEBACKs for now only
+        if (cpkt->cmd == MemCmd::Writeback) {
+            // make sure that the sender actually had the line
+            panic_if(sf_item.requested & req_port, "double request :( "\
+                     "SF value %x.%x\n", sf_item.requested, sf_item.holder);
+            panic_if(!(sf_item.holder & req_port), "requester %x is not a "\
+                     "holder :( SF value %x.%x\n", req_port,
+                     sf_item.requested, sf_item.holder);
+            // Writebacks -> the sender does not have the line anymore
+            sf_item.holder &= ~req_port;
+        } else {
+            assert(0 == "Handle non-writeback, here");
+        }
+        DPRINTF(SnoopFilter, "%s:   new SF value %x.%x\n",
+                __func__,  sf_item.requested, sf_item.holder);
+    }
+}
+
+std::pair<SnoopFilter::SnoopList, Cycles>
+SnoopFilter::lookupSnoop(const Packet* cpkt)
+{
+    DPRINTF(SnoopFilter, "%s: packet addr 0x%x cmd %s\n",
+            __func__, cpkt->getAddr(), cpkt->cmdString());
+
+    assert(cpkt->isRequest());
+
+    // Broadcast / filter upward snoops
+    const bool filter_upward = true;  // @todo: Make configurable
+
+    if (!filter_upward)
+        return snoopAll(lookupLatency);
+
+    Addr line_addr = cpkt->getAddr() & ~(linesize - 1);
+    SnoopItem& sf_item = cachedLocations[line_addr];
+
+    DPRINTF(SnoopFilter, "%s:   old SF value %x.%x\n",
+            __func__, sf_item.requested, sf_item.holder);
+
+    SnoopMask interested = (sf_item.holder | sf_item.requested);
+    assert(cpkt->isInvalidate() == cpkt->needsExclusive());
+    if (cpkt->isInvalidate() && !sf_item.requested) {
+        // Early clear of the holder, if no other request is currently going on
+        // @todo: This should possibly be updated even though we do not filter
+        // upward snoops
+        sf_item.holder = 0;
+    }
+
+    DPRINTF(SnoopFilter, "%s:   new SF value %x.%x interest: %x \n",
+            __func__, sf_item.requested, sf_item.holder, interested);
+
+    return snoopSelected(maskToPortList(interested), lookupLatency);
+}
+
+void
+SnoopFilter::updateSnoopResponse(const Packet* cpkt,
+                                 const SlavePort& rsp_port,
+                                 const SlavePort& req_port)
+{
+    DPRINTF(SnoopFilter, "%s: packet rsp %s req %s addr 0x%x cmd %s\n",
+            __func__, rsp_port.name(), req_port.name(), cpkt->getAddr(),
+            cpkt->cmdString());
+
+    Addr line_addr = cpkt->getAddr() & ~(linesize - 1);
+    SnoopMask rsp_mask = portToMask(rsp_port);
+    SnoopMask req_mask = portToMask(req_port);
+    SnoopItem& sf_item = cachedLocations[line_addr];
+
+    assert(cpkt->isResponse());
+    assert(cpkt->memInhibitAsserted());
+
+    DPRINTF(SnoopFilter, "%s:   old SF value %x.%x\n",
+            __func__,  sf_item.requested, sf_item.holder);
+
+    // The source should have the line
+    panic_if(!(sf_item.holder & rsp_mask), "SF value %x.%x does not have "\
+             "the line\n", sf_item.requested, sf_item.holder);
+
+    // The destination should have had a request in
+    panic_if(!(sf_item.requested & req_mask), "SF value %x.%x missing "\
+             "the original request\n",  sf_item.requested, sf_item.holder);
+
+    // Update the residency of the cache line.
+    if (cpkt->needsExclusive() || !cpkt->sharedAsserted()) {
+        DPRINTF(SnoopFilter, "%s:  dropping %x because needs: %i shared: %i "\
+                "SF val: %x.%x\n", __func__,  rsp_mask,
+                cpkt->needsExclusive(), cpkt->sharedAsserted(),
+                sf_item.requested, sf_item.holder);
+
+        sf_item.holder &= ~rsp_mask;
+        // The snoop filter does not see any ACKs from non-responding sharers
+        // that have been invalidated :(  So below assert would be nice, but..
+        //assert(sf_item.holder == 0);
+        sf_item.holder = 0;
+    }
+    assert(cpkt->cmd != MemCmd::Writeback);
+    sf_item.holder |=  req_mask;
+    sf_item.requested &= ~req_mask;
+    DPRINTF(SnoopFilter, "%s:   new SF value %x.%x\n",
+            __func__, sf_item.requested, sf_item.holder);
+}
+
+void
+SnoopFilter::updateSnoopForward(const Packet* cpkt,
+        const SlavePort& rsp_port, const MasterPort& req_port)
+{
+    DPRINTF(SnoopFilter, "%s: packet rsp %s req %s addr 0x%x cmd %s\n",
+            __func__, rsp_port.name(), req_port.name(), cpkt->getAddr(),
+            cpkt->cmdString());
+
+    Addr line_addr = cpkt->getAddr() & ~(linesize - 1);
+    SnoopItem& sf_item = cachedLocations[line_addr];
+    SnoopMask rsp_mask M5_VAR_USED = portToMask(rsp_port);
+
+    assert(cpkt->isResponse());
+    assert(cpkt->memInhibitAsserted());
+
+    DPRINTF(SnoopFilter, "%s:   old SF value %x.%x\n",
+            __func__,  sf_item.requested, sf_item.holder);
+
+    // Remote (to this snoop filter) snoops update the filter already when they
+    // arrive from below, because we may not see any response.
+    if (cpkt->needsExclusive()) {
+        // If the request to this snoop response hit an in-flight transaction,
+        // the holder was not reset -> no assertion & do that here, now!
+        //assert(sf_item.holder == 0);
+        sf_item.holder = 0;
+    }
+    DPRINTF(SnoopFilter, "%s:   new SF value %x.%x\n",
+            __func__, sf_item.requested, sf_item.holder);
+}
+
+void
+SnoopFilter::updateResponse(const Packet* cpkt, const SlavePort& slave_port)
+{
+    DPRINTF(SnoopFilter, "%s: packet src %s addr 0x%x cmd %s\n",
+            __func__, slave_port.name(), cpkt->getAddr(), cpkt->cmdString());
+
+    Addr line_addr = cpkt->getAddr() & ~(linesize - 1);
+    SnoopMask slave_mask = portToMask(slave_port);
+    SnoopItem& sf_item = cachedLocations[line_addr];
+
+    assert(cpkt->isResponse());
+
+    DPRINTF(SnoopFilter, "%s:   old SF value %x.%x\n",
+            __func__,  sf_item.requested, sf_item.holder);
+
+    // Make sure we have seen the actual request, too
+    panic_if(!(sf_item.requested & slave_mask), "SF value %x.%x missing "\
+             "request bit\n", sf_item.requested, sf_item.holder);
+
+    // Update the residency of the cache line.
+    if (cpkt->needsExclusive() || !cpkt->sharedAsserted())
+        sf_item.holder = 0;
+    sf_item.holder |=  slave_mask;
+    sf_item.requested &= ~slave_mask;
+    DPRINTF(SnoopFilter, "%s:   new SF value %x.%x\n",
+            __func__, sf_item.requested, sf_item.holder);
+}
+
+SnoopFilter *
+SnoopFilterParams::create()
+{
+    return new SnoopFilter(this);
+}
diff --git a/src/mem/snoop_filter.hh b/src/mem/snoop_filter.hh
new file mode 100755
index 000000000..c1bb65dfc
--- /dev/null
+++ b/src/mem/snoop_filter.hh
@@ -0,0 +1,260 @@
+/*
+ * Copyright (c) 2013 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 <stephan.diestelhorst@arm.com>
+ */
+
+/**
+ * @file
+ * Definition of a snoop filter.
+ */
+
+#ifndef __MEM_SNOOP_FILTER_HH__
+#define __MEM_SNOOP_FILTER_HH__
+
+#include <utility>
+
+#include "base/hashmap.hh"
+#include "mem/packet.hh"
+#include "mem/port.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<SlavePort*> SnoopList;
+
+    SnoopFilter (const SnoopFilterParams *p) : SimObject(p),
+        linesize(p->system->cacheLineSize()), lookupLatency(p->lookup_latency)
+    {
+    }
+
+    /**
+     * Init a new snoop filter and tell it about all the slave ports of the
+     * enclosing bus.
+     *
+     * @param bus_slave_ports Vector of slave ports that the bus is attached to.
+     */
+    void setSlavePorts(const std::vector<SlavePort*>& bus_slave_ports) {
+        slavePorts = bus_slave_ports;
+    }
+
+    /**
+     * 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.
+     *
+     * @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 a successful request, update all data structures in the snoop filter
+     * reflecting the changes caused by that request
+     *
+     * @param cpkt          Pointer to the request packet.  Not changed.
+     * @param slave_port    Slave port where the request came from.
+     * @param will_retry    This request will retry on this bus / snoop filter
+     */
+    void updateRequest(const Packet* cpkt, const SlavePort& slave_port,
+                       bool will_retry);
+
+    /**
+     * 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 leaves this cluster.
+     */
+    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);
+
+    /**
+     * Simple factory methods for standard return values for lookupRequest
+     */
+    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);
+    }
+
+  protected:
+    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;
+    };
+    /**
+     * 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;
+    /**
+     * Convert multiple ports to a corresponding bitmask
+     * @param ports SnoopList that should be converted.
+     * @return Bitmask corresponding to the ports in the list.
+     */
+    SnoopMask portListToMask(const SnoopList& ports) 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:
+    /** Simple hash set of cached addresses. */
+    m5::hash_map<Addr, SnoopItem> cachedLocations;
+    /** List of all attached slave ports. */
+    SnoopList slavePorts;
+    /** Cache line size. */
+    const unsigned linesize;
+    /** Latency for doing a lookup in the filter */
+    const Cycles lookupLatency;
+};
+
+inline SnoopFilter::SnoopMask
+SnoopFilter::portToMask(const SlavePort& port) const
+{
+    unsigned id = (unsigned)port.getId();
+    assert(id != (unsigned)InvalidPortID);
+    assert((int)id < 8 * sizeof(SnoopMask));
+
+    return ((SnoopMask)1) << id;
+}
+
+inline SnoopFilter::SnoopMask
+SnoopFilter::portListToMask(const SnoopList& ports) const
+{
+    SnoopMask m = 0;
+    for (auto port = ports.begin(); port != ports.end(); ++port)
+        m |= portToMask(**port);
+    return m;
+}
+
+inline SnoopFilter::SnoopList
+SnoopFilter::maskToPortList(SnoopMask port_mask) const
+{
+    SnoopList res;
+    for (auto port = slavePorts.begin(); port != slavePorts.end(); ++port)
+        if (port_mask & portToMask(**port))
+            res.push_back(*port);
+    return res;
+}
+#endif // __MEM_SNOOP_FILTER_HH__