Re: [RFC PATCH 0/4] Add support for LZ4-compressed kernels


Andrew Morton
 

On Sat, 26 Jan 2013 14:50:43 +0900
Kyungsik Lee <kyungsik.lee@...> wrote:

This patchset is for supporting LZ4 compressed kernel and initial ramdisk on
the x86 and ARM architectures.

According to http://code.google.com/p/lz4/, LZ4 is a very fast lossless
compression algorithm and also features an extremely fast decoder.

Kernel Decompression APIs are based on implementation by Yann Collet
(http://code.google.com/p/lz4/source/checkout).
De/compression Tools are also provided from the site above.

The initial test result on ARM(v7) based board shows that the size of kernel
with LZ4 compressed is 8% bigger than LZO compressed but the decompressing
speed is faster(especially under the enabled unaligned memory access).

Test: 3.4 based kernel built with many modules
Uncompressed kernel size: 13MB
lzo: 6.3MB, 301ms
lz4: 6.8MB, 251ms(167ms, with enabled unaligned memory access)

It seems that it___s worth trying LZ4 compressed kernel image or ramdisk
for making the kernel boot more faster.

...

20 files changed, 663 insertions(+), 3 deletions(-)

...
What's this "with enabled unaligned memory access" thing? You mean "if
the arch supports CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS"? If so,
that's only x86, which isn't really in the target market for this
patch, yes?

It's a lot of code for a 50ms boot-time improvement. Does anyone have
any opinions on whether or not the benefits are worth the cost?

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