tlb_coalescer.hh

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#ifndef __ARCH_AMDGPU_VEGA_TLB_COALESCER_HH__
#define __ARCH_AMDGPU_VEGA_TLB_COALESCER_HH__
 
#include <list>
#include <queue>
#include <string>
#include <vector>
 
#include "arch/amdgpu/vega/tlb.hh"
#include "base/statistics.hh"
#include "mem/port.hh"
#include "mem/request.hh"
#include "params/VegaTLBCoalescer.hh"
#include "sim/clocked_object.hh"
 
namespace gem5
{
 
class Packet;
class ThreadContext;
 
class VegaTLBCoalescer : public ClockedObject
{
  public:
    VegaTLBCoalescer(const VegaTLBCoalescerParams &p);
    ~VegaTLBCoalescer() { }
 
    // Number of TLB probes per cycle. Parameterizable - default 2.
    int TLBProbesPerCycle;
 
    // Consider coalescing across that many ticks.
    // Paraemterizable - default 1.
    int coalescingWindow;
 
    // Each coalesced request consists of multiple packets
    // that all fall within the same virtual page
    typedef std::vector<PacketPtr> coalescedReq;
 
    // disables coalescing when true
    bool disableCoalescing;
 
    /*
     * This is a hash map with <tick_index> as a key.
     * It contains a vector of coalescedReqs per <tick_index>.
     * Requests are buffered here until they can be issued to
     * the TLB, at which point they are copied to the
     * issuedTranslationsTable hash map.
     *
     * In terms of coalescing, we coalesce requests in a given
     * window of x cycles by using tick_index = issueTime/x as a
     * key, where x = coalescingWindow. issueTime is the issueTime
     * of the pkt from the ComputeUnit's perspective, but another
     * option is to change it to curTick(), so we coalesce based
     * on the receive time.
     */
    typedef std::map<Tick, std::vector<coalescedReq>> CoalescingFIFO;
 
    CoalescingFIFO coalescerFIFO;
 
    /*
     * issuedTranslationsTable: a hash_map indexed by virtual page
     * address. Each hash_map entry has a vector of PacketPtr associated
     * with it denoting the different packets that share an outstanding
     * coalesced translation request for the same virtual page.
     *
     * The rules that determine which requests we can coalesce are
     * specified in the canCoalesce() method.
     */
    typedef std::unordered_map<Addr, coalescedReq> CoalescingTable;
 
    CoalescingTable issuedTranslationsTable;
 
    // number of packets the coalescer receives
    statistics::Scalar uncoalescedAccesses;
    // number packets the coalescer send to the TLB
    statistics::Scalar coalescedAccesses;
 
    // Number of cycles the coalesced requests spend waiting in
    // coalescerFIFO. For each packet the coalescer receives we take into
    // account the number of all uncoalesced requests this pkt "represents"
    statistics::Scalar queuingCycles;
 
    // On average how much time a request from the
    // uncoalescedAccesses that reaches the TLB
    // spends waiting?
    statistics::Scalar localqueuingCycles;
    statistics::Scalar localCycles;
  // localqueuingCycles/uncoalescedAccesses
    statistics::Formula localLatency;
   // latency of a request to be completed
    statistics::Formula latency;
 
    bool canCoalesce(PacketPtr pkt1, PacketPtr pkt2);
    void updatePhysAddresses(PacketPtr pkt);
    void regStats() override;
 
    class CpuSidePort : public ResponsePort
    {
      public:
        CpuSidePort(const std::string &_name, VegaTLBCoalescer *tlb_coalescer,
                    PortID _index)
            : ResponsePort(_name, tlb_coalescer), coalescer(tlb_coalescer),
              index(_index) { }
 
      protected:
        VegaTLBCoalescer *coalescer;
        int index;
 
        virtual bool recvTimingReq(PacketPtr pkt);
        virtual Tick recvAtomic(PacketPtr pkt) { return 0; }
        virtual void recvFunctional(PacketPtr pkt);
        virtual void recvRangeChange() { }
        virtual void recvReqRetry();
 
        virtual void
        recvRespRetry()
        {
            fatal("recvRespRetry() is not implemented in the TLB "
                "coalescer.\n");
        }
 
        virtual AddrRangeList getAddrRanges() const;
    };
 
    class MemSidePort : public RequestPort
    {
      public:
        MemSidePort(const std::string &_name, VegaTLBCoalescer *tlb_coalescer,
                    PortID _index)
            : RequestPort(_name, tlb_coalescer), coalescer(tlb_coalescer),
              index(_index) { }
 
        std::deque<PacketPtr> retries;
 
      protected:
        VegaTLBCoalescer *coalescer;
        int index;
 
        virtual bool recvTimingResp(PacketPtr pkt);
        virtual Tick recvAtomic(PacketPtr pkt) { return 0; }
        virtual void recvFunctional(PacketPtr pkt);
        virtual void recvRangeChange() { }
        virtual void recvReqRetry();
 
        virtual void
        recvRespRetry()
        {
            fatal("recvRespRetry() not implemented in TLB coalescer");
        }
    };
 
    // Coalescer response ports on the cpu Side
    std::vector<CpuSidePort*> cpuSidePort;
    // Coalescer request ports on the memory side
    std::vector<MemSidePort*> memSidePort;
 
    Port &getPort(const std::string &if_name,
                  PortID idx=InvalidPortID) override;
 
    void processProbeTLBEvent();
    EventFunctionWrapper probeTLBEvent;
 
    void processCleanupEvent();
    EventFunctionWrapper cleanupEvent;
 
    int tlb_level;
    int maxDownstream;
    unsigned int numDownstream;
    CpuSidePort *stalledPort;
    std::queue<CpuSidePort *> stalledPortsQueue;
    // enforce uniqueness in queue
    std::map<CpuSidePort *, CpuSidePort *> stalledPortsMap;
 
    unsigned int availDownstreamSlots() {
        assert(tlb_level == 1);
        return maxDownstream - numDownstream;
    }
 
    void insertStalledPortIfNotMapped(CpuSidePort *);
    bool mustStallCUPort(CpuSidePort *);
 
    bool stalledPorts() {
        assert(tlb_level == 1);
      return stalledPortsQueue.size() > 0;
    }
 
    void decrementNumDownstream() {
        assert(tlb_level == 1);
        assert(numDownstream > 0);
        numDownstream--;
    }
 
    void incrementNumDownstream() {
        assert(tlb_level == 1);
        assert(maxDownstream >= numDownstream);
        numDownstream++;
    }
 
    void unstallPorts();
 
 
    // this FIFO queue keeps track of the virt. page
    // addresses that are pending cleanup
    std::queue<Addr> cleanupQueue;
};
 
} // namespace gem5
 
#endif // __ARCH_AMDGPU_VEGA_TLB_COALESCER_HH__