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

[Andrew Morton <akpm@linux-foundation.org>]

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