libc/src/time/gpu/nanosleep.cpp

   1 //===-- GPU implementation of the nanosleep function ----------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "src/time/nanosleep.h"
  10
  11 #include "time_utils.h"
  12
  13 namespace LIBC_NAMESPACE {
  14
  15 constexpr uint64_t TICKS_PER_NS = 1000000000UL;
  16
  17 LLVM_LIBC_FUNCTION(int, nanosleep,
  18                    (const struct timespec *req, struct timespec *rem)) {
  19   if (!GPU_CLOCKS_PER_SEC || !req)
  20     return -1;
  21
  22   uint64_t nsecs = req->tv_nsec + req->tv_sec * TICKS_PER_NS;
  23
  24   uint64_t start = gpu::fixed_frequency_clock();
  25 #if defined(LIBC_TARGET_ARCH_IS_NVPTX) && __CUDA_ARCH__ >= 700
  26   uint64_t end = start + nsecs / (TICKS_PER_NS / GPU_CLOCKS_PER_SEC);
  27   uint64_t cur = gpu::fixed_frequency_clock();
  28   // The NVPTX architecture supports sleeping and guaruntees the actual time
  29   // slept will be somewhere between zero and twice the requested amount. Here
  30   // we will sleep again if we undershot the time.
  31   while (cur < end) {
  32     LIBC_INLINE_ASM("nanosleep.u32 %0;" ::"r"(nsecs));
  33     cur = gpu::fixed_frequency_clock();
  34     nsecs -= nsecs > cur - start ? cur - start : 0;
  35   }
  36 #elif defined(LIBC_TARGET_ARCH_IS_AMDGPU)
  37   uint64_t end = start + nsecs / (TICKS_PER_NS / GPU_CLOCKS_PER_SEC);
  38   uint64_t cur = gpu::fixed_frequency_clock();
  39   // The AMDGPU architecture does not provide a sleep implementation with a
  40   // known delay so we simply repeatedly sleep with a large value of ~960 clock
  41   // cycles and check until we've passed the time using the known frequency.
  42   __builtin_amdgcn_s_sleep(2);
  43   while (cur < end) {
  44     __builtin_amdgcn_s_sleep(15);
  45     cur = gpu::fixed_frequency_clock();
  46   }
  47 #else
  48   // Sleeping is not supported.
  49   if (rem) {
  50     rem->tv_sec = req->tv_sec;
  51     rem->tv_nsec = req->tv_nsec;
  52   }
  53   return -1;
  54 #endif
  55   uint64_t stop = gpu::fixed_frequency_clock();
  56
  57   // Check to make sure we slept for at least the desired duration and set the
  58   // remaining time if not.
  59   uint64_t elapsed = (stop - start) * (TICKS_PER_NS / GPU_CLOCKS_PER_SEC);
  60   if (elapsed < nsecs) {
  61     if (rem) {
  62       rem->tv_sec = (nsecs - elapsed) / TICKS_PER_NS;
  63       rem->tv_nsec = (nsecs - elapsed) % TICKS_PER_NS;
  64     }
  65     return -1;
  66   }
  67
  68   return 0;
  69 }
  70
  71 } // namespace LIBC_NAMESPACE