Impact of Hyper Threading on x264 encoding

[Stereodude]

Following some observations that were made in another thread I decided to test the impact of hyperthreading on x264 encoding.

I used a i7-2600k @ 4.3gHz under Windows 7 x64. Decoding was done using DGdecNV. x264 8bit 64-bit version r2008 was used. I did a 2 pass encode of the first 5 minutes (7193 frames) of Star Trek (2009) at a target bitrate of 20868kbit/sec. The first pass was run using placebo and was reused for all the subsequent encodes.

First pass:

x264.exe --bitrate 20868 --frames 7193 --preset placebo --tune film --weightp 1 --bframes 3 --ref 4 --bluray-compat --b-adapt 2 --vbv-maxrate 40000 --vbv-bufsize 30000 --level 4.1 --keyint 24 --open-gop --slices 4 --colorprim "bt709" --transfer "bt709" --colormatrix "bt709" --sar 1:1 --pass 1 --qpfile ST11.chp -o NUL ST11.AVS

Second passes:

"C:\HDTV Tools\x264\x264.exe" --bitrate 20868 --frames 7193 --preset xxxxx --tune film --weightp 1 --bframes 3 --ref 4 --bluray-compat --vbv-maxrate 40000 --vbv-bufsize 30000 --level 4.1 --keyint 24 --open-gop --slices 4 --colorprim "bt709" --transfer "bt709" --colormatrix "bt709" --sar 1:1 --pass 2 --qpfile ST11.chp -o ST11_xxxxx.264 ST11.AVS

Results:

Setting		HT on	HT off	Improvement
placebo		39:29	51:28	23.28%
veryslow	22:56	28:22	19.15%
slower		15:53	19:43	19.44%
slow		06:37	08:17	20.12%
medium		05:01	06:18	20.37%
fast		04:15	05:17	19.56%
faster		03:10	03:57	19.83%
veryfast	02:05	02:23	12.59%
superfast	02:04	02:04	0.00%
ultrafast	02:04	02:04	0.00%