[FFmpeg-user] libx264 very bad scaling with 4 real CPU cores (no HT)

[D]

Another test: this time I built ffmpeg myself according to 
https://trac.ffmpeg.org/wiki/CompilationGuide/Ubuntu
And here's the benchmark -- Very bad scaling:

$ time ffmpeg -i a.mp4 -c:v libx264 -crf 23 -threads 1 -c:a libvorbis 
b.mp4 -y
real    9m51.886s

$ time ffmpeg -i a.mp4 -c:v libx264 -crf 23 -threads 2 -c:a libvorbis 
b.mp4 -y
real    5m14.630s

$ time ffmpeg -i a.mp4 -c:v libx264 -crf 23 -threads 3 -c:a libvorbis 
b.mp4 -y
real    4m11.611s
(should be: 9m51.886s / 3 = 3,28m)

$ time ffmpeg -i a.mp4 -c:v libx264 -crf 23 -threads 4 -c:a libvorbis 
b.mp4 -y
real    3m27.341s
(should be: 9m51.886s / 4 = 2,46m -- as slow as 3 threads)


Another test -- Even worse scaling:
$ time ffmpeg -i a.mp4 -c:v libx264 -crf 23 -preset ultrafast -threads 1 
-c:a libvorbis b.mp4 -y
real    0m59.384s

$ time ffmpeg -i a.mp4 -c:v libx264 -crf 23 -preset ultrafast -threads 2 
-c:a libvorbis b.mp4 -y
real    0m37.741s

$ time ffmpeg -i a.mp4 -c:v libx264 -crf 23 -preset ultrafast -threads 3 
-c:a libvorbis b.mp4 -y
real    0m34.870s

$ time ffmpeg -i a.mp4 -c:v libx264 -crf 23 -preset ultrafast -threads 4 
-c:a libvorbis b.mp4 -y
real    0m34.400s

If I'm not the only one having this issue, then the devs should fix this.

On 27.11.2015 17:04, D wrote:
> Here's the normal: http://pastebin.com/wyt56q4B
> And here's with debug: http://pastebin.com/WxfRDKPP
> (Upgraded to Ubuntu 15.10 that's why you see "gcc 5.2.1")
>
> It was a bit slower this time after OS Upgrade -- same command and 
> everything otherwise:
> Ubuntu 15.04: 3m22
> Ubuntu 15.10: 3m45
> Anyway, this is not the priority right now.
>
> On 27.11.2015 16:15, James Darnley wrote:
>> On 2015-11-27 13:29, D wrote:
>>> Nevermind, libx264 isn't doing much better:
>> Have you posted the full output of ffmpeg somewhere in this thread?
>>
>>
>>
>>
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