On Tue, Jan 16, 2024 at 10:20:38AM +0100, Paul de Weerd wrote: > What Stuart said is very true - here's what I saw on my 16-core > machine with SMT enabled while encoding a Blu-Ray movie:
Out of interest, what exactly do you mean by "encoding a Blu-Ray movie"? Are you encoding source files for recording to a blu-ray video disc, or transcoding an existing blu-ray video disc to another format? A few years ago, I was working on a project which involved assembling about 400 source clips into a ~4 hour long documentary, using ffmpeg in a script to create the final output which was a single massive '.nut' file encoded with motion jpeg and pcm audio, (about 90 Gb of output video data). The workstation had 32 Gb of physical RAM and eight physical CPU cores. I had to disable two cores in the BIOS because the large number of ffmpeg threads was demanding more than 32 Gb of physical RAM, and adding swap did not help. Only by disabling some cores did the memory requirements reduce enough to complete the encoding. I later hacked the ffmpeg source to make it use fewer cores than hw.ncpufound and re-enabled them in the BIOS. (And shortly after we upgraded the machine to 64 GB of RAM.) So this is another issue to consider with lots of cores - memory requirements typically increase for the same workload.
