[OLPC-devel] good news

Fri Jul 28 23:47:02 EDT 2006

Ron,

that's really Great News(tm)!

3 things come to mind which I would like to change to be able to support lzma compression:
- uncompressed kernel image (no idea right now)
- uncompressed initrd (easy)
- compress the elfImage in one go

Even if we only compress the initrd with lzma (instead of gzip -9) and leave the rest untouched, we have drastic savings:
-rw-r--r-- 1 compiler users 239741 2006-07-29 03:18 initrd.gz
-rw-r--r-- 1 compiler users 191753 2006-07-29 04:59 initrd.lzma

Considering the additional potential for the kernel:
-rw-r--r-- 1 compiler users 514266 2006-07-29 02:34 vmlinux.bin.gz
-rw-r--r-- 1 compiler users 445959 2006-07-29 05:14 vmlinux.bin.lzma

That makes a total saving of over 116 kb! However, the decompression code is not zero cost. It weighs in at ~9 kb, so the net savings would be 107 kb which is still impressive.

Compressing the ELF image in one go instead of compressing kernel and initrd individually can save an additional 1-5 kb and we wouldn't have to patch the kernel for it.

Further savings (1-8 kb) can be achieved by varying compression options, but the more things you want to try, the longer the build will take, so that would only make sense directly before shipping.

If we also compress the VSA with lzma, it gets just under 32 kb, so we save an additional 32 kb.

A total saving of 139 kb is quite a lot and gives us enough room to include a few additional features.

What do you think?

Regards,
Carl-Daniel
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