snoop_filter.hh

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#ifndef __MEM_SNOOP_FILTER_HH__
#define __MEM_SNOOP_FILTER_HH__
 
#include <bitset>
#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"
 
namespace gem5
{
 
class SnoopFilter : public SimObject
{
  public:
 
    // Change for systems with more than 256 ports tracked by this object
    static const int SNOOP_MASK_SIZE = 256;
 
    typedef std::vector<QueuedResponsePort*> SnoopList;
 
    SnoopFilter (const SnoopFilterParams &p) :
        SimObject(p), reqLookupResult(cachedLocations.end()),
        linesize(p.system->cacheLineSize()), lookupLatency(p.lookup_latency),
        maxEntryCount(p.max_capacity / p.system->cacheLineSize()),
        stats(this)
    {
    }
 
    void setCPUSidePorts(const SnoopList& _cpu_side_ports) {
        localResponsePortIds.resize(_cpu_side_ports.size(), InvalidPortID);
 
        PortID id = 0;
        for (const auto& p : _cpu_side_ports) {
            // no need to track this port if it is not snooping
            if (p->isSnooping()) {
                cpuSidePorts.push_back(p);
                localResponsePortIds[p->getId()] = id++;
            }
        }
 
        // make sure we can deal with this many ports
        fatal_if(id > SNOOP_MASK_SIZE,
                 "Snoop filter only supports %d snooping ports, got %d\n",
                 SNOOP_MASK_SIZE, id);
    }
 
    std::pair<SnoopList, Cycles> lookupRequest(const Packet* cpkt,
                                        const ResponsePort& cpu_side_port);
 
    void finishRequest(bool will_retry, Addr addr, bool is_secure);
 
    std::pair<SnoopList, Cycles> lookupSnoop(const Packet* cpkt);
 
    void updateSnoopResponse(const Packet *cpkt, const ResponsePort& rsp_port,
                             const ResponsePort& req_port);
 
    void updateSnoopForward(const Packet *cpkt, const ResponsePort& rsp_port,
                            const RequestPort& req_port);
 
    void updateResponse(const Packet *cpkt, const ResponsePort& cpu_side_port);
 
    virtual void regStats();
 
  protected:
 
    typedef std::bitset<SNOOP_MASK_SIZE> SnoopMask;
 
    struct SnoopItem
    {
        SnoopMask requested;
        SnoopMask holder;
    };
    typedef std::unordered_map<Addr, SnoopItem> SnoopFilterCache;
 
    std::pair<SnoopList, Cycles> snoopAll(Cycles latency) const
    {
        return std::make_pair(cpuSidePorts, latency);
    }
    std::pair<SnoopList, Cycles> snoopSelected(const SnoopList&
                                _cpu_side_ports, Cycles latency) const
    {
        return std::make_pair(_cpu_side_ports, latency);
    }
    std::pair<SnoopList, Cycles> snoopDown(Cycles latency) const
    {
        SnoopList empty;
        return std::make_pair(empty , latency);
    }
 
    SnoopMask portToMask(const ResponsePort& port) const;
    SnoopList maskToPortList(SnoopMask ports) const;
 
  private:
 
    void eraseIfNullEntry(SnoopFilterCache::iterator& sf_it);
 
    SnoopFilterCache cachedLocations;
 
    struct ReqLookupResult
    {
        SnoopFilterCache::iterator it;
 
        SnoopItem retryItem;
 
        ReqLookupResult(SnoopFilterCache::iterator end_it)
            : it(end_it), retryItem{0, 0}
        {
        }
        ReqLookupResult() = delete;
    } reqLookupResult;
 
    SnoopList cpuSidePorts;
    std::vector<PortID> localResponsePortIds;
    const unsigned linesize;
    const Cycles lookupLatency;
    const unsigned maxEntryCount;
 
    enum LineStatus
    {
        LineSecure = 0x01,
    };
 
    struct SnoopFilterStats : public statistics::Group
    {
        SnoopFilterStats(statistics::Group *parent);
 
        statistics::Scalar totRequests;
        statistics::Scalar hitSingleRequests;
        statistics::Scalar hitMultiRequests;
 
        statistics::Scalar totSnoops;
        statistics::Scalar hitSingleSnoops;
        statistics::Scalar hitMultiSnoops;
    } stats;
};
 
inline SnoopFilter::SnoopMask
SnoopFilter::portToMask(const ResponsePort& port) const
{
    assert(port.getId() != InvalidPortID);
    // if this is not a snooping port, return a zero mask
    return !port.isSnooping() ? 0 :
        ((SnoopMask)1) << localResponsePortIds[port.getId()];
}
 
inline SnoopFilter::SnoopList
SnoopFilter::maskToPortList(SnoopMask port_mask) const
{
    SnoopList res;
    for (const auto& p : cpuSidePorts)
        if ((port_mask & portToMask(*p)).any())
            res.push_back(p);
    return res;
}
 
} // namespace gem5
 
#endif // __MEM_SNOOP_FILTER_HH__