[OpenBIOS] [PATCH 0/8] RFC: OFMEM cleanup/memory reduction patch

Mark Cave-Ayland mark.cave-ayland at ilande.co.uk
Fri Apr 13 17:56:52 CEST 2012

On 10/04/12 18:41, Blue Swirl wrote:

> Yes, but again, image size savings are not very interesting. Savings
> in image loading time is easily lost during decompression.

Well, the use case I'm considering at the moment is that if you build 
OpenBIOS SPARC32 with -O0 -g and then try to load it into QEMU, QEMU 
reports that the image is too large. So I'm guessing this is a 
limitation of the memory layout of the machine, rather than the space 
occupied by the binary.

>> Secondly, if we're copying the data to an OFMEM-allocated area then why
>> don't we just compress it at build time and then decompress it during the
>> copy using DEFLATE (see my previous email)? Then we can further reduce the
>> dictionary payload size from ~180K to around ~37K, although as you rightly
>> point out there could be a small delay on startup - given the small size
>> involved (and the fact we can lock the TLB entry like we do with the Forth
>> machine), I don't think the penalty will be too bad.
> But only the decompressed result is what matters wrt memory usage,
> isn't it? After Forth has started, there shouldn't be any difference
> in RAM use, except that the decompressor code takes more space.

Again for the use case above, this would not be a problem if we were to 
decompress and relocate the dictionary into RAM.

>> I'm fairly confident I can come up with an experimental patch for this -
>> would people mind if we added zlib as a build-time dependency, and puff.c to
>> the OpenBIOS codebase? At the very least, if the decompression appears too
>> expensive the first stage on its own would still be a good idea.
> For maximum compression, bzImage (still remember those?) style
> approach could be used for whole image.

I can't say I've ever looked at that. But if you're happy to at least 
consider a patch, then I'd like to invest some time looking at this.



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