snoop_filter.hh

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 * Authors: Stephan Diestelhorst
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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"

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<QueuedSlavePort*> 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())
    {
    }

    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 > 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 SlavePort& slave_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 SlavePort& rsp_port,
                             const SlavePort& req_port);

    void updateSnoopForward(const Packet *cpkt, const SlavePort& rsp_port,
                            const MasterPort& req_port);

    void updateResponse(const Packet *cpkt, const SlavePort& slave_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(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);
    }

    SnoopMask portToMask(const SlavePort& 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 slavePorts;
    std::vector<PortID> localSlavePortIds;
    const unsigned linesize;
    const Cycles lookupLatency;
    const unsigned maxEntryCount;

    enum LineStatus {
        LineSecure = 0x01,
    };

    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)).any())
            res.push_back(p);
    return res;
}

#endif // __MEM_SNOOP_FILTER_HH__