On Fri, 7 Jun 2024, Martin Storsjö wrote:
The default timer register pmccntr_el0 usually requires enabling access with e.g. a kernel module. --- cntvct_el0 has significantly better resolution than av_gettime_relative (while the unscaled nanosecond output of clock_gettime is much higher resolution).In one tested case, the cntvct_el0 timer has a frequency of 25 MHz (readable via the register cntfrq_el0). --- libavutil/aarch64/timer.h | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/libavutil/aarch64/timer.h b/libavutil/aarch64/timer.h index fadc9568f8..966f17081a 100644 --- a/libavutil/aarch64/timer.h +++ b/libavutil/aarch64/timer.h @@ -33,7 +33,16 @@ static inline uint64_t read_time(void) uint64_t cycle_counter; __asm__ volatile( "isb \t\n" +#if defined(__ANDROID__) + // cntvct_el0 has lower resolution than pmccntr_el0, but is usually + // accessible from user space by default. + "mrs %0, cntvct_el0 " +#else + // pmccntr_el0 has higher resolution, but is usually not accessible + // from user space by default (but access can be enabled with a custom + // kernel module). "mrs %0, pmccntr_el0 " +#endif : "=r"(cycle_counter) :: "memory" );
Zhao, does this implementation seem useful to you? Does it give you better (more accurate, less noisy?) benchmarking numbers on Android, than the fallback based on clock_gettime?
// Martin _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
