[Libdlo] Compression support in udlfb?

Bernie Thompson bernie at plugable.com
Sat May 29 08:45:13 PDT 2010

Hi Florian,

On my side, what time I've had over the last months in udlfb has been
focused on improving the pipeline in the context of RLE-style
compression. RLE is less of a burden on the system -- keeping a big
lookup table in the CPU cache for the huffman-style approach is a
significant impact. This is especially a consideration for scenerios
like the terminal case where we've got 10+ displaylink devices sharing
one system, or for embedded/ARM CPUs (SheevaPlug, etc.)

With RLE, and because of a mix of other factors (keeping code
small/simple, staying 16bpp), Linux is already outperforming Windows
7, Vista, Mac, and in many cases Windows XP, in many of the common
scenarios (e.g. normal application use and web browsing).  Among other
things, that's been a deterrent from spending time going a different

But the tradeoff is on video playback, compiz (if it worked), etc.,
where huffman-like encoding is a clear win.

So any patches would be definitely be welcome and valuable -- because
of the tradeoffs, it would be good to have at least simple
configurability of it as an option (udlfb has generally been using
sysfs attributes to turn on/off options -- that would be a good way).
And there is a reasonably good system of metrics in place right now in
udlfb, to easily measure the impact of any improvement.

Best wishes,

On Sat, May 29, 2010 at 12:23 AM, Florian Echtler <floe at butterbrot.org> wrote:
> Hello everybody,
> I've been quite busy over the last year, so I haven't really followed
> the state of udlfb closely. I was wondering if anybody is currently
> working on adding compression support? If not, I'd be curious about the
> reasons why and might give it a try myself if time permits.
> Florian
> --
> 0666 - Filemode of the Beast
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