Question about the efficiency with different num_threads set

[huhanwj]

I am trying to push for higher frame extraction speed for a UHD video with 30M bitrate as the 12 frames are extracted by

frame_batch = vr.get_batch(frame_indices).asnumpy()

I am using a Xeon Platinum 8360Y, which has 36 cores, and using cProfile to track the execution time of each function call, and I surprisingly find that when I set

• num_thread=0 (which is auto), the line of code takes 22.733s
• num_thread=1, 12.784s
• num_thread=2, 14.255s
• num_thread=4, 15.855s
• num_thread=6, 17.310s
• num_thread=8, 18.587s
• num_thread=10, 19.813s
• num_thread=12, 20.735s
• num_thread=16, 22.702s
• num_thread=24, 25.357s
• num_thread=36, 25.763s
• num_thread=48, 25.817s
• num_thread=64, 26.388s
• num_thread=72, 26.486s

Does this mean that the less threads, the better running speed?

[huhanwj]

Same behavior on AMD Ryzen 9 7900X and Intel Core i9-12900K, and only happens when dealing with UHD or higher resolution videos (4K, 8K) , anyone has any clue on it?