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/*! \file
    \brief Benchmark helpers for Distributed GEMM

    A delay kernel to gate all GEMMs across devices, controlled by a flag that
    the host will set off once it launches DistGEMM across all devices.

    DistGpuTimer extends cutlass's existing cudaEvent-based timer to multiple devices.
*/

#pragma once

#include <iostream>
#include <cuda/atomic>
#include <cuda/std/atomic>


namespace cutlass {

/////////////////////////////////////////////////////////////////////////////////////////////////
/// Delay kernel
/////////////////////////////////////////////////////////////////////////////////////////////////

using AtomicBoolean = cuda::atomic<bool>;

__global__ void delay_kernel(const AtomicBoolean* atomic_flag_ptr) {
  while (not atomic_flag_ptr->load()) {
    __nanosleep(40);
  }
}


/////////////////////////////////////////////////////////////////////////////////////////////////
/// Distributed GPU Timer
/// Sets up cuda events for multiple processors.
/////////////////////////////////////////////////////////////////////////////////////////////////
template <int NP>
struct DistGpuTimer {
  int _primary_device;
  cudaEvent_t _start[NP];
  cudaEvent_t _stop[NP];

  /// Constructor
  DistGpuTimer()
  {
    CUDA_CHECK(cudaGetDevice(&_primary_device));
    for (int device = 0; device < NP; ++device) {
      CUDA_CHECK(cudaSetDevice(device));
      CUDA_CHECK(cudaEventCreate(&_start[device]));
      CUDA_CHECK(cudaEventCreate(&_stop[device]));
    }
    CUDA_CHECK(cudaSetDevice(_primary_device));
  }

  /// Destructor
  ~DistGpuTimer()
  {
    for (int device = 0; device < NP; ++device) {
      CUDA_CHECK(cudaSetDevice(device));
      CUDA_CHECK(cudaEventDestroy(_start[device]));
      CUDA_CHECK(cudaEventDestroy(_stop[device]));
    }
    CUDA_CHECK(cudaSetDevice(_primary_device));
  }

  /// Start the timer for a given stream (defaults to the default stream)
  void start(int device, cudaStream_t stream) {
    assert(device >= 0 && device < NP);
    CUDA_CHECK(cudaEventRecord(_start[device], stream));
  }

  /// Stop the timer
  void stop(int device, cudaStream_t stream) {
    assert(device >= 0 && device < NP);
    CUDA_CHECK(cudaEventRecord(_stop[device], stream));
  }

  /// Return the elapsed time (in milliseconds)
  float elapsed_millis(int device) {
    assert(device >= 0 && device < NP);
    float elapsed = 0.0;
    CUDA_CHECK(cudaEventSynchronize(_stop[device]));
    CUDA_CHECK(cudaEventElapsedTime(&elapsed, _start[device], _stop[device]));
    return elapsed;
  }
};

} //namespace cutlass