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 "src/__support/common.h"
  12 #include "src/__support/macros/config.h"
  13 #include "src/__support/time/gpu/time_utils.h"
  14
  15 namespace LIBC_NAMESPACE_DECL {
  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_SEC;
  23   uint64_t tick_rate = TICKS_PER_SEC / GPU_CLOCKS_PER_SEC;
  24
  25   uint64_t start = gpu::fixed_frequency_clock();
  26 #if defined(LIBC_TARGET_ARCH_IS_NVPTX)
  27   uint64_t end = start + (nsecs + tick_rate - 1) / tick_rate;
  28   uint64_t cur = gpu::fixed_frequency_clock();
  29   // The NVPTX architecture supports sleeping and guaruntees the actual time
  30   // slept will be somewhere between zero and twice the requested amount. Here
  31   // we will sleep again if we undershot the time.
  32   while (cur < end) {
  33     if (__nvvm_reflect("__CUDA_ARCH") >= 700)
  34       LIBC_INLINE_ASM("nanosleep.u32 %0;" ::"r"(nsecs));
  35     cur = gpu::fixed_frequency_clock();
  36     nsecs -= nsecs > cur - start ? cur - start : 0;
  37   }
  38 #elif defined(LIBC_TARGET_ARCH_IS_AMDGPU)
  39   uint64_t end = start + (nsecs + tick_rate - 1) / tick_rate;
  40   uint64_t cur = gpu::fixed_frequency_clock();
  41   // The AMDGPU architecture does not provide a sleep implementation with a
  42   // known delay so we simply repeatedly sleep with a large value of ~960 clock
  43   // cycles and check until we've passed the time using the known frequency.
  44   __builtin_amdgcn_s_sleep(2);
  45   while (cur < end) {
  46     __builtin_amdgcn_s_sleep(15);
  47     cur = gpu::fixed_frequency_clock();
  48   }
  49 #else
  50   // Sleeping is not supported.
  51   if (rem) {
  52     rem->tv_sec = req->tv_sec;
  53     rem->tv_nsec = req->tv_nsec;
  54   }
  55   return -1;
  56 #endif
  57   uint64_t stop = gpu::fixed_frequency_clock();
  58
  59   // Check to make sure we slept for at least the desired duration and set the
  60   // remaining time if not.
  61   uint64_t elapsed = (stop - start) * tick_rate;
  62   if (elapsed < nsecs) {
  63     if (rem) {
  64       rem->tv_sec = (nsecs - elapsed) / TICKS_PER_SEC;
  65       rem->tv_nsec = (nsecs - elapsed) % TICKS_PER_SEC;
  66     }
  67     return -1;
  68   }
  69
  70   return 0;
  71 }
  72
  73 } // namespace LIBC_NAMESPACE_DECL