Louwrentius

The system i'm running is a Core i7 920 @ 3.6 Ghz.

I am transcoding a DVD (Grave Of The Fire Flies) to iPod format (640x480 x264).

Thread support is enabled, to FFmpeg uses about 250% CPU. That's 2.5 of the 4 cores available. If possible, I would have liked to see it use all four to the max.

Any way. I use these settings:

FFmpeg version SVN-r18628

ffmpeg -i $1 -pass 1 -acodec libfaac -ab 128k -ac 2 -vcodec libx264 -vpre normal -vpre ipod640 -s 640x480 -b 512k -bt 512k -threads 0 -f mp4 $2

With these settings, I get an encoding speed of fps=193.

I don't know how that stacks up against other systems. It seems fast to me though. In effect, the system is playing the DVD at 7.6 times the speed of the movie (25 fps?). So encoding is 88 minutes / 7.6 = 11.45 minutes for encoding a DVD to iPod x264.

Even today, Core 2 Duo processors clocked at 2 ghz are no slugs. However, the Core i7 920 is of a different kind. First, it is not only clocked at a higher speed (default 2,8 Ghz), it is also a quad-core processor. Thanks to the re- introduction of hyperthreading, this processor can handle 8 parallel proceses simultaneously.

Just how fast a Core i7 can be, especially if overclocked to 3,6 Ghz shows this diagram:

Using my still in development version of PPSS, four systems processed 400 GB of WAV files and converted them to MP3. This simple pie-chart shows that the Core i7 on it's own, using 8 parallel processes, managed to process 2/3 of the files. The Core i7 was way faster than the other 3 systems combined! This is marvelous, I think. And it seems all due to Hyperthreading. If an additional duo core system would have been added, the other systems combined would have also 8 parallel threads available and would have processed roughly 50% of the items. However, please note that the Core i7 is a quad core processor and has 'only' four physical cores...

I had some wave files that I wanted to encode to mp3. I wrote a small parallel processing framework for this job. It executes parallel jobs so I can benefit from the 4 cores + 4 virtual cores of my new Core 7i 920 processor. 

The framework is based on some shell scripts running on Linux (or probably any other unix) and Lame.

I wanted to test how much impact hyperthreading has on parallel performance. Hyperthreading has a bit of a bad reputation, dating back from the P4 erra. Lots of 'hype' but no significant performance gain. 

I ran some test with hyperthreading enabled and disabled (within the bios). 

In this test I used 16 wav files and encoded them to mp3 with Lame under Linux. The data in the table are raw measurements.

As you can see, the benefit of HT is there and can improve processing speed with up to 24 percent. 

As more threads are run simultaneously, processing speed is significantly improved comparted to non-HT.