Opportunity for speedup

Bobby Powers bobbypowers at gmail.com
Thu Feb 19 13:41:20 EST 2009

On Thu, Feb 19, 2009 at 1:22 PM, C. Scott Ananian <cscott at laptop.org> wrote:
> I'd suggest just uncompressing the various image files and re-timing
> as a start.  The initial implementation was uncompressed, but people
> complained about space usage on the emulator images (which are
> uncompressed).  The current code supports both uncompressed and
> compressed image formats.  For uncompressed images, putting the bits
> on the screen is an mmap and memcpy, so I can't imagine any
> implementation being faster than that (it's possible, of course, that
> what's stealing CPU is the shell's invocation of the client program;
> recoding just that little part in C should be trivial, since it does
> nothing but write to a socket IIRC.)
> Anyway, further benchmarking of the current implementation is probably
> worthwhile before a complete reimplementation is called for.  But if
> you want to reimplement it from scratch, go nuts.
>  --scott

I already re-implemented it - it was a fun optimization project and
introduction to lower level systems programming.  Using Mitch's D565
format to keep track of only the parts of the image that change cut
down the implementation size significantly.  Its now only 2
uncompressed images (frame00.565 and ul-warning.565), and <300KB of
differences for the animation sequence.  I understand reads from video
memory (which I think is what the framebuffer is?) can be extremely
slow, so it could turn out faster to open a D565 file, mmap it and
mcpy the several tens of kilobytes of differences to the framebuffer
than it is to read those differences from one part of video memory to

This is where benchmarking should give some clearer answers.


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