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How ffmpeg scales with additional cores/threads

 
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choekstr



Joined: 06 Dec 2008
Posts: 152

PostPosted: Sat Nov 21, 2009 7:39 pm    Post subject: How ffmpeg scales with additional cores/threads Reply with quote

I just ran across this interesting set of metrics that shows some definitive numbers for how ffmpeg scales with the number of threads it receives. As we all know, this is controlled by '-threads X' in our pytivo.conf file and is limited by how many processors, cores, and whether one has Hyperthreading support or not.

Here is a benchmark (chromium media_bench) of number of threads on an 8 core / 16 thread Nehalem.
It shows performance continues to improve beyond [the previous limited] 8 threads.

Threads vs Time/Frame (ms)
1 13.14
2 7.31
3 5.73
4 4.07
5 4.50
6 3.82
7 3.21
8 2.93
9 2.62
10 2.40
11 2.19
12 2.03
13 1.92
14 1.83
15 1.76
16 1.70

Obviously there are other limitations that control how fast content downloads such as bandwidth, the Tivo data accept rate, etc. Interesting nevertheless to know if upgrading cores or getting a nice new Core i5 or i7 will make a performance difference.

BTW, using a Q6600 Core2Quad I am able to realize > realtime with 1080p content so a 16 thread processor really isn't necessary...Just cool. Wink

--
Chris
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choekstr



Joined: 06 Dec 2008
Posts: 152

PostPosted: Wed Sep 01, 2010 1:45 pm    Post subject: Reply with quote

FWIW, I was able to get > realtime transferring 1080p because I had set my bitrate to 12M a while back and forgot about it. We have seen the max transfer rates of the Tivo around 14-15Mbps so the general use of 16M doesn't afford realtime transfer despite the transcoding cpu muscle you throw at it.
Now with the Tivo Premier, that baby flies!
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ToeCutter



Joined: 03 Sep 2010
Posts: 4

PostPosted: Sat Sep 18, 2010 8:46 pm    Post subject: Reply with quote

Good deal, thanks for investigating this.

Looks like 4 threads is the sweet spot before the rule of diminishing returns sets in?

I've been tweaking and testing the results, but you've saved us alot of work by posting this.

Thanks!
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