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d1a6cb195f
Improves the accuracy of measurements, especially in short sections. To quote the Intel 64 and IA-32 Architectures Software Developer's Manual: "The RDTSC instruction is not a serializing instruction. It does not necessarily wait until all previous instructions have been executed before reading the counter. Similarly, subsequent instructions may begin execution before the read operation is performed. If software requires RDTSC to be executed only after all previous instructions have completed locally, it can either use RDTSCP (if the processor supports that instruction) or execute the sequence LFENCE;RDTSC." SSE2 is a requirement for lfence so only use it on SSE2-capable systems. Prefer lfence;rdtsc over rdtscp since rdtscp is supported on fewer systems. Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
50 lines
1.3 KiB
C
50 lines
1.3 KiB
C
/*
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* copyright (c) 2006 Michael Niedermayer <michaelni@gmx.at>
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*
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* This file is part of Libav.
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*
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* Libav is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* Libav 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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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with Libav; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#ifndef AVUTIL_X86_TIMER_H
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#define AVUTIL_X86_TIMER_H
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#include <stdint.h>
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#if HAVE_INLINE_ASM
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#define AV_READ_TIME read_time
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static inline uint64_t read_time(void)
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{
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uint32_t a, d;
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__asm__ volatile(
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#if ARCH_X86_64 || defined(__SSE2__)
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"lfence \n\t"
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#endif
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"rdtsc \n\t"
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: "=a" (a), "=d" (d));
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return ((uint64_t)d << 32) + a;
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}
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#elif HAVE_RDTSC
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#include <intrin.h>
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#define AV_READ_TIME __rdtsc
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#endif /* HAVE_INLINE_ASM */
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#endif /* AVUTIL_X86_TIMER_H */
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