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

kyungsik.lee <kyungsik.lee@...>

On 2013-01-30 오전 6:09, Rajesh Pawar wrote:
Andrew Morton <akpm@...> wrote:

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 [[,]] 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
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
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?
BTW, what happened to the proposed LZO update - woudn't it better to merge this first?

Also, under the hood LZ4 seems to be quite similar to LZO, so probably
LZO speed would also greatly benefit from unaligned access and some other
ARM optimisations
I didn't test with the proposed LZO update you mentioned. Sorry, which one do you mean?
I did some tests with the latest LZO in the mainline.

As a result, LZO is not faster in an unaligned access enabled on ARM. Actually Slower.

Decompression time: 336ms(383ms, with unaligned access enabled)

You may refer to to know more about it.



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