libc/benchmarks/gpu/timing/amdgpu/timing.h

//===------------- AMDGPU implementation of timing utils --------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_LIBC_UTILS_GPU_TIMING_AMDGPU
#define LLVM_LIBC_UTILS_GPU_TIMING_AMDGPU

#include "src/__support/CPP/array.h"
#include "src/__support/CPP/type_traits.h"
#include "src/__support/GPU/utils.h"
#include "src/__support/common.h"
#include "src/__support/macros/attributes.h"
#include "src/__support/macros/config.h"

#include <stdint.h>

namespace LIBC_NAMESPACE_DECL {

// Returns the overhead associated with calling the profiling region. This
// allows us to substract the constant-time overhead from the latency to
// obtain a true result. This can vary with system load.
[[gnu::noinline]] static LIBC_INLINE uint64_t overhead() {
  gpu::memory_fence();
  uint64_t start = gpu::processor_clock();
  uint32_t result = 0.0;
  asm("v_or_b32 %[v_reg], 0, %[v_reg]\n" ::[v_reg] "v"(result));
  asm("" ::"s"(start));
  uint64_t stop = gpu::processor_clock();
  return stop - start;
}

// Profile a simple function and obtain its latency in clock cycles on the
// system. This function cannot be inlined or else it will disturb the very
// delicate balance of hard-coded dependencies.
template <typename F, typename T>
[[gnu::noinline]] static LIBC_INLINE uint64_t latency(F f, T t) {
  // We need to store the input somewhere to guarantee that the compiler
  // will not constant propagate it and remove the profiling region.
  volatile T storage = t;
  T arg = storage;

  // The AMDGPU architecture needs to wait on pending results.
  gpu::memory_fence();
  // Get the current timestamp from the clock.
  uint64_t start = gpu::processor_clock();

  // This forces the compiler to load the input argument and run the clock
  // cycle counter before the profiling region.
  asm("" ::"s"(start));

  // Run the function under test and return its value.
  auto result = f(arg);

  // This inline assembly performs a no-op which forces the result to both
  // be used and prevents us from exiting this region before it's complete.
  if constexpr (cpp::is_same_v<decltype(result), char> ||
                cpp::is_same_v<decltype(result), bool>)
    // AMDGPU does not support input register constraints for i1 and i8, so we
    // cast it to a 32-bit integer. This does not add an additional assembly
    // instruction (https://godbolt.org/z/zxGqv8G91).
    asm("v_or_b32 %[v_reg], 0, %[v_reg]\n" ::[v_reg] "v"(
        static_cast<uint32_t>(result)));
  else
    asm("v_or_b32 %[v_reg], 0, %[v_reg]\n" ::[v_reg] "v"(result));

  // Obtain the current timestamp after running the calculation and force
  // ordering.
  uint64_t stop = gpu::processor_clock();
  asm("" ::"s"(stop));
  gpu::memory_fence();

  // Return the time elapsed.
  return stop - start;
}

template <typename F, typename T1, typename T2>
[[gnu::noinline]] static LIBC_INLINE uint64_t latency(F f, T1 t1, T2 t2) {
  volatile T1 storage1 = t1;
  volatile T2 storage2 = t2;
  T1 arg1 = storage1;
  T2 arg2 = storage2;

  gpu::memory_fence();
  uint64_t start = gpu::processor_clock();

  asm("" ::"s"(start));

  auto result = f(arg1, arg2);

  if constexpr (cpp::is_same_v<decltype(result), char> ||
                cpp::is_same_v<decltype(result), bool>)
    asm("v_or_b32 %[v_reg], 0, %[v_reg]\n" ::[v_reg] "v"(
        static_cast<uint32_t>(result)));
  else
    asm("v_or_b32 %[v_reg], 0, %[v_reg]\n" ::[v_reg] "v"(result));

  uint64_t stop = gpu::processor_clock();
  asm("" ::"s"(stop));
  gpu::memory_fence();

  return stop - start;
}

// Provides throughput benchmarking.
template <typename F, typename T, size_t N>
[[gnu::noinline]] static LIBC_INLINE uint64_t
throughput(F f, const cpp::array<T, N> &inputs) {
  asm("" ::"v"(&inputs));

  gpu::memory_fence();
  uint64_t start = gpu::processor_clock();

  asm("" ::"s"(start));

  for (auto input : inputs) {
    auto result = f(input);

    asm("" ::"v"(result));
  }

  uint64_t stop = gpu::processor_clock();
  asm("" ::"s"(stop));
  gpu::memory_fence();

  // Return the time elapsed.
  return stop - start;
}

// Provides throughput benchmarking for 2 arguments (e.g. atan2())
template <typename F, typename T, size_t N>
[[gnu::noinline]] static LIBC_INLINE uint64_t throughput(
    F f, const cpp::array<T, N> &inputs1, const cpp::array<T, N> &inputs2) {
  asm("" ::"v"(&inputs1), "v"(&inputs2));

  gpu::memory_fence();
  uint64_t start = gpu::processor_clock();

  asm("" ::"s"(start));

  for (size_t i = 0; i < inputs1.size(); i++) {
    auto result = f(inputs1[i], inputs2[i]);

    asm("" ::"v"(result));
  }

  uint64_t stop = gpu::processor_clock();
  asm("" ::"s"(stop));
  gpu::memory_fence();

  // Return the time elapsed.
  return stop - start;
}

} // namespace LIBC_NAMESPACE_DECL

#endif // LLVM_LIBC_UTILS_GPU_TIMING_AMDGPU