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86 lines
3.5 KiB
C
86 lines
3.5 KiB
C
/* Copyright (C) 2001 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 <time.h>
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#include "cpuclock-init.h"
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#include "libc-internal.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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/* 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 unsigned long long int freq;
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/* We need the starting time for the process. */
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CPUCLOCK_VARDECL (_dl_cpuclock_offset);
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/* This function is defined in the thread library. */
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extern void __pthread_clock_settime (unsigned long long int offset)
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__attribute__ ((__weak__));
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/* We add an limitation here: we assume that the process is not
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running as long as it takes to wrap-around the 64-bit timestamp
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counter. On a 4GHz machine it would take 136 years of uptime to
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wrap around so this "limitation" is not severe. */
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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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unsigned long long int tsc; \
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unsigned long long int usertime; \
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\
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/* First thing is to get the current time. */ \
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asm volatile ("rdtsc" : "=A" (tsc)); \
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\
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if (__builtin_expect (freq == 0, 0)) \
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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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\
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/* Convert the user-provided time into CPU ticks. */ \
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usertime = tp->tv_sec * freq + (tp->tv_nsec * freq) / 1000000000ull; \
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\
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/* Determine the offset and use it as the new base value. */ \
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if (clock_id != CLOCK_THREAD_CPUTIME_ID \
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|| __pthread_clock_settime == NULL) \
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_dl_cpuclock_offset = tsc - usertime; \
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else \
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__pthread_clock_settime (tsc - usertime); \
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} \
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break;
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#include <sysdeps/unix/clock_settime.c>
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