[libc] Add Timing Utils for AMDGPU

libc/benchmarks/gpu/timing/amdgpu/CMakeLists.txt

@@ -0,0 +1,7 @@
+add_header_library(
+  amdgpu_timing
+  HDRS
+    timing.h
+  DEPENDS
+    libc.src.__support.common
+)

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

@@ -0,0 +1,73 @@
+//===------------- 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/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 {
+
+// 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 uint32_t storage = t;
+  float arg = storage;
+  asm("" ::"s"(arg));
+
+  // 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"(arg), "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.
+  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;
+}
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_UTILS_GPU_TIMING_AMDGPU

libc/benchmarks/gpu/timing/timing.h

@@ -12,7 +12,7 @@
 #include "src/__support/macros/properties/architectures.h"
 
 #if defined(LIBC_TARGET_ARCH_IS_AMDGPU)
-#error "amdgpu not yet supported"
+#include "amdgpu/timing.h"
 #elif defined(LIBC_TARGET_ARCH_IS_NVPTX)
 #include "nvptx/timing.h"
 #else