abef15cd81
of the timehands, from the kern_tc.c implementation to vdso. Add comments giving hints where to look for the algorithm explanation. To compensate the removal of rmb() in userspace binuptime(), add explicit lfence instruction before rdtsc. On i386, add usual complications to detect SSE2 presence; assume that old CPUs which do not implement SSE2 also execute rdtsc almost in order. Reviewed by: alc, bde (previous version) Sponsored by: The FreeBSD Foundation MFC after: 2 weeks
148 lines
3.9 KiB
C
148 lines
3.9 KiB
C
/*-
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* Copyright (c) 2012 Konstantin Belousov <kib@FreeBSD.org>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/elf.h>
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#include <sys/time.h>
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#include <sys/vdso.h>
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#include <errno.h>
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#include <time.h>
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#include <machine/atomic.h>
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#include "libc_private.h"
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static u_int
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tc_delta(const struct vdso_timehands *th)
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{
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return ((__vdso_gettc(th) - th->th_offset_count) &
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th->th_counter_mask);
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}
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/*
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* Calculate the absolute or boot-relative time from the
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* machine-specific fast timecounter and the published timehands
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* structure read from the shared page.
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*
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* The lockless reading scheme is similar to the one used to read the
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* in-kernel timehands, see sys/kern/kern_tc.c:binuptime(). This code
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* is based on the kernel implementation.
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*/
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static int
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binuptime(struct bintime *bt, struct vdso_timekeep *tk, int abs)
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{
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struct vdso_timehands *th;
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uint32_t curr, gen;
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do {
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if (!tk->tk_enabled)
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return (ENOSYS);
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curr = atomic_load_acq_32(&tk->tk_current);
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th = &tk->tk_th[curr];
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if (th->th_algo != VDSO_TH_ALGO_1)
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return (ENOSYS);
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gen = atomic_load_acq_32(&th->th_gen);
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*bt = th->th_offset;
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bintime_addx(bt, th->th_scale * tc_delta(th));
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if (abs)
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bintime_add(bt, &th->th_boottime);
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/*
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* Ensure that the load of th_offset is completed
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* before the load of th_gen.
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*/
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atomic_thread_fence_acq();
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} while (curr != tk->tk_current || gen == 0 || gen != th->th_gen);
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return (0);
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}
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static struct vdso_timekeep *tk;
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#pragma weak __vdso_gettimeofday
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int
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__vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
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{
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struct bintime bt;
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int error;
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if (tz != NULL)
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return (ENOSYS);
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if (tk == NULL) {
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error = __vdso_gettimekeep(&tk);
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if (error != 0 || tk == NULL)
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return (ENOSYS);
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}
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if (tk->tk_ver != VDSO_TK_VER_CURR)
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return (ENOSYS);
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error = binuptime(&bt, tk, 1);
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if (error != 0)
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return (error);
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bintime2timeval(&bt, tv);
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return (0);
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}
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#pragma weak __vdso_clock_gettime
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int
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__vdso_clock_gettime(clockid_t clock_id, struct timespec *ts)
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{
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struct bintime bt;
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int abs, error;
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if (tk == NULL) {
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error = _elf_aux_info(AT_TIMEKEEP, &tk, sizeof(tk));
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if (error != 0 || tk == NULL)
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return (ENOSYS);
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}
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if (tk->tk_ver != VDSO_TK_VER_CURR)
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return (ENOSYS);
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switch (clock_id) {
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case CLOCK_REALTIME:
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case CLOCK_REALTIME_PRECISE:
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case CLOCK_REALTIME_FAST:
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case CLOCK_SECOND:
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abs = 1;
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break;
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case CLOCK_MONOTONIC:
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case CLOCK_MONOTONIC_PRECISE:
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case CLOCK_MONOTONIC_FAST:
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case CLOCK_UPTIME:
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case CLOCK_UPTIME_PRECISE:
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case CLOCK_UPTIME_FAST:
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abs = 0;
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break;
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default:
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return (ENOSYS);
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}
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error = binuptime(&bt, tk, abs);
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if (error != 0)
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return (error);
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bintime2timespec(&bt, ts);
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if (clock_id == CLOCK_SECOND)
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ts->tv_nsec = 0;
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return (0);
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}
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