/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│ │ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi │ ╞══════════════════════════════════════════════════════════════════════════════╡ │ Copyright 2022 Justine Alexandra Roberts Tunney │ │ │ │ Permission to use, copy, modify, and/or distribute this software for │ │ any purpose with or without fee is hereby granted, provided that the │ │ above copyright notice and this permission notice appear in all copies. │ │ │ │ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │ │ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │ │ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │ │ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │ │ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │ │ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │ │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │ │ PERFORMANCE OF THIS SOFTWARE. │ ╚─────────────────────────────────────────────────────────────────────────────*/ #include "libc/atomic.h" #include "libc/calls/struct/timespec.h" #include "libc/cosmo.h" #include "libc/errno.h" #include "libc/nexgen32e/rdtsc.h" #include "libc/nexgen32e/x86feature.h" /** * @fileoverview Fast Monotonic Clock Polyfill for XNU/NT. */ static struct { atomic_uint once; struct timespec base_wall; uint64_t base_tick; } g_mono; static void sys_clock_gettime_mono_init(void) { g_mono.base_wall = timespec_real(); g_mono.base_tick = rdtsc(); } int sys_clock_gettime_mono(struct timespec *time) { uint64_t nanos; uint64_t cycles; #ifdef __x86_64__ // intel architecture guarantees that a mapping exists between rdtsc & // nanoseconds only if the cpu advertises invariant timestamps support if (!X86_HAVE(INVTSC)) return -EINVAL; #endif cosmo_once(&g_mono.once, sys_clock_gettime_mono_init); cycles = rdtsc() - g_mono.base_tick; // this is a crude approximation, that's worked reasonably well so far // only the kernel knows the actual mapping between rdtsc and nanosecs // which we could attempt to measure ourselves using clock_gettime but // we'd need to impose 100 ms of startup latency for a guess this good nanos = cycles / 3; *time = timespec_add(g_mono.base_wall, timespec_fromnanos(nanos)); return 0; }