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The default timer register pmccntr_el0 usually requires enabling access with e.g. a kernel module (while it is accessible by default on Windows). On Linux, the default for checkasm benchmarks is to use perf (if suitable headers are available) though. On macOS, using cntvct_el0 gives measurements with the same magnitude as mach_absolute_time (which is used currently), but possibly with a little less overhead/noise. Signed-off-by: Martin Storsjö <martin@martin.st>
54 lines
1.7 KiB
C
54 lines
1.7 KiB
C
/*
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* Copyright (c) 2015 Janne Grunau <janne-libav@jannau.net>
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg 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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* FFmpeg 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 FFmpeg; 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_AARCH64_TIMER_H
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#define AVUTIL_AARCH64_TIMER_H
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#include <stdint.h>
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#include "config.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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uint64_t cycle_counter;
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__asm__ volatile(
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"isb \t\n"
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#if defined(__ANDROID__) || defined(__APPLE__)
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// cntvct_el0 has lower resolution than pmccntr_el0, but is usually
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// accessible from user space by default.
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"mrs %0, cntvct_el0 "
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#else
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// pmccntr_el0 has higher resolution, but is usually not accessible
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// from user space by default (but access can be enabled with a custom
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// kernel module).
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"mrs %0, pmccntr_el0 "
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#endif
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: "=r"(cycle_counter) :: "memory" );
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return cycle_counter;
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}
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#endif /* HAVE_INLINE_ASM */
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#endif /* AVUTIL_AARCH64_TIMER_H */
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