global_memory_pipeline.hh

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/*
 * Copyright (c) 2014-2015 Advanced Micro Devices, Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 * this list of conditions and the following disclaimer.
 *
 * 2. 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.
 *
 * 3. Neither the name of the copyright holder 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
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#ifndef __GLOBAL_MEMORY_PIPELINE_HH__
#define __GLOBAL_MEMORY_PIPELINE_HH__
 
#include <queue>
#include <string>
 
#include "base/statistics.hh"
#include "base/stats/group.hh"
#include "gpu-compute/misc.hh"
#include "params/ComputeUnit.hh"
#include "sim/stats.hh"
 
/*
 * @file global_memory_pipeline.hh
 *
 * The global memory pipeline issues newly created global memory packets
 * from the pipeline to DTLB. The exec() method of the memory packet issues
 * the packet to the DTLB if there is space available in the return fifo.
 * This stage also retires previously issued loads and stores that have
 * returned from the memory sub-system.
 */
 
namespace gem5
{
 
class ComputeUnit;
 
class GlobalMemPipeline
{
  public:
    GlobalMemPipeline(const ComputeUnitParams &p, ComputeUnit &cu);
    void init();
    void exec();
 
    GPUDynInstPtr getNextReadyResp();
 
    void completeRequest(GPUDynInstPtr gpuDynInst);
 
    void issueRequest(GPUDynInstPtr gpuDynInst);
 
    void handleResponse(GPUDynInstPtr gpuDynInst);
 
    bool
    isGMReqFIFOWrRdy(uint32_t pendReqs=0) const
    {
        return (gmIssuedRequests.size() + pendReqs) < gmQueueSize;
    }
 
    const std::string &name() const { return _name; }
    void
    incLoadVRFBankConflictCycles(int num_cycles)
    {
        stats.loadVrfBankConflictCycles += num_cycles;
    }
 
    bool coalescerReady(GPUDynInstPtr mp) const;
    bool outstandingReqsCheck(GPUDynInstPtr mp) const;
 
    void acqCoalescerToken(GPUDynInstPtr mp);
 
  private:
    ComputeUnit &computeUnit;
    const std::string _name;
    int gmQueueSize;
    int maxWaveRequests;
 
    // Counters to track the inflight loads and stores
    // so that we can provide the proper backpressure
    // on the number of inflight memory operations.
    int inflightStores;
    int inflightLoads;
 
    // The size of global memory.
    int globalMemSize;
 
    /*
     * This buffer holds the memory responses in order data - the responses
     * are ordered by their unique sequence number, which is monotonically
     * increasing. When a memory request returns its "done" flag is set to
     * true. During each tick the the GM pipeline will check if the oldest
     * request is finished, and if so it will be removed from the queue.
     *
     * key:   memory instruction's sequence ID
     *
     * value: pair holding the instruction pointer and a bool that
     *        is used to indicate whether or not the request has
     *        completed
     */
    std::map<uint64_t, std::pair<GPUDynInstPtr, bool>> gmOrderedRespBuffer;
 
    // Global Memory Request FIFO: all global memory requests
    // are issued to this FIFO from the memory pipelines
    std::queue<GPUDynInstPtr> gmIssuedRequests;
 
  protected:
    struct GlobalMemPipelineStats : public statistics::Group
    {
        GlobalMemPipelineStats(statistics::Group *parent);
 
        // number of cycles of delaying the update of a VGPR that is the
        // target of a load instruction (or the load component of an atomic)
        // The delay is due to VRF bank conflicts
        statistics::Scalar loadVrfBankConflictCycles;
    } stats;
};
 
} // namespace gem5
 
#endif // __GLOBAL_MEMORY_PIPELINE_HH__