77 lines
3.1 KiB
C
77 lines
3.1 KiB
C
/* Copyright (C) 1999, 2000 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Library General Public License as
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published by the Free Software Foundation; either version 2 of the
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License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public
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License along with the GNU C Library; see the file COPYING.LIB. If not,
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write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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Boston, MA 02111-1307, USA. */
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#include <sys/param.h>
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#include <sys/time.h>
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/* This implementation uses the TSC register in modern (i586 and up) IA-32
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processors (most modern clones also provide it). Since we need the
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resolution of the clock and since determining this is not cheap, we
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cache the value. But this means that systems with processors running
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at different speeds or process migration to machines with slower or
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faster processors will not work without changes. */
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/* Function to determine processor frequency. */
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extern unsigned long long int __get_clockfreq (void);
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/* Clock frequency of the processor. We make it a 64-bit variable
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because some jokers are already playing with processors with more
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than 4GHz. */
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static long int nsec;
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/* We add an limitation here: we assume that the machine is not up as
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long as it takes to wrap-around the 64-bit timestamp counter. On a
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4GHz machine it would take 136 years of uptime to wrap around so
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this "limitation" is not severe.
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We use this clock also as the monotonic clock since we don't allow
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setting the CPU-time clock. If this should ever change we will have
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to separate the two. */
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#define EXTRA_CLOCK_CASES \
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case CLOCK_PROCESS_CPUTIME_ID: \
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case CLOCK_THREAD_CPUTIME_ID: \
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{ \
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if (__builtin_expect (nsec == 0, 0)) \
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{ \
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unsigned long long int freq; \
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\
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/* This can only happen if we haven't initialized the `freq' \
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variable yet. Do this now. We don't have to protect this \
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code against multiple execution since all of them should \
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lead to the same result. */ \
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freq = __get_clockfreq (); \
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if (__builtin_expect (freq == 0, 0)) \
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/* Something went wrong. */ \
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break; \
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\
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nsec = MAX (1000000000ULL / freq, 1); \
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} \
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\
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/* File in the values. The seconds are always zero (unless we \
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have a 1Hz machine). */ \
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res->tv_sec = 0; \
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res->tv_nsec = nsec; \
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\
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retval = 0; \
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} \
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break;
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#include <sysdeps/posix/clock_getres.c>
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