On Fri, Jan 1, 2016 at 8:07 AM, Ganesh Ajjanagadde <gajja...@mit.edu> wrote: > Hi all, > > Motivated by a remark by Ronald: > https://ffmpeg.org/pipermail/ffmpeg-devel/2016-January/186200.html, > this is a request for comment on disabling compile time tablegen for > cbrt if the total cycle count < 200000. Note that cbrt tables are only > used in aacdec.
To start some effort towards a more principled understanding of the costs of runtime table initialization, I did some benchmarks. Note: I am not familiar with avcodec, so I don't know if this reflects correctly the static vs dynamic cost. file: ~/samples/aac/al04_44.mp4 stream_loop: 100 number of calls of avcodec_decode_audio4: 35956 cost per call (avcodec_decode_audio4): 834030 decicycles in decode_audio4, 1 runs, 0 skips 556200 decicycles in decode_audio4, 2 runs, 0 skips [...] 177365 decicycles in decode_audio4, 16384 runs, 0 skips 177059 decicycles in decode_audio4, 32768 runs, 0 skips decoding cost: 17706*35956 = 636,636,936 cycles duration: 832.55 seconds cost per second of audio: 764,683 cycles cost of table init: 200,000 cycles fraction: 0.26 So in a clip of n seconds duration, the relative overhead of dynamic initialization of these cbrt tables is 0.26/n. For a more concrete number, say a clip is of 180 seconds duration, then the overhead is 0.26/180 = 0.15%. _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
