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Re: Floating point performance

To: Matej Kupljen <matej.kupljen@ultra.si>
Subject: Re: Floating point performance
From: David Daney <ddaney@avtrex.com>
Date: Thu, 29 Sep 2005 08:39:18 -0700
Cc: Ulrich Eckhardt <Eckhardt@satorlaser.com>, linux-mips@linux-mips.org
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Matej Kupljen wrote:
Hi


I've built soft float toolchain (with crosstool) and then build
MPlayer with it. The performance is very low. I cannot even play the
mp3 file with MPlayer on DBAU1200 with 400MHz CPU!

[...]

Any other suggestions?

I'm not sure what you are doing, but if you only want to play music, I'd use Ogg Vorbis instead, which has a decoder that only uses integer arithmetic for exactly the case of FPU-less machines and the Au1200. I could also imagine an MP3 decoder written for integer only being written somewhere, but I don't know anything about it.


Yes, I can use madplay (libmad) for music only, which uses int
arithmetics (also special version for MIPS).

But I also want to play video and currently I am testing this with
MPlayer (maybe I'll add support for MAE, sometime in the future).
Then I found out, that MPlayer can use libmad for MP3 and it
works great know.


We are using libmad and can play 128kbps MP3s on a mips 300MHz 4kc code with about 10-15% CPU utilization.

However I think anything but very low resolution low frame rate video is out of the question. You need several orders of magnitude more processing power to make it work. All of the MIPS based video systems that I am aware of (TiVo, Sony and Samsung HDTVs etc.) have dedicated hardware video decoders. There are people talking about doing the decoding purely in software, but they would be using something with the processing power of a 2GHz Pentium4 with special DSP extensions. As far as I know these are just paper designs and are not yet in production.

I guess what I am trying to say is that even if you could make the soft float library four times faster, you would still be no where close to being able to decode video.

I declare it impossible, but encourage you to prove me wrong.

David Daney.

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