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


H. Peter Anvin <hpa@...>
 

Uhm... you're saying we have to be at one extreme or the other?

We probably could drop the legacy lzma format, but someone might rely on it.

Nicolas Pitre <nico@...> wrote:

On Mon, 28 Jan 2013, Andrew Morton 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 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?
I'm guessing this is referring to commit 5010192d5a.

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?
Well, we used to have only one compressed format. Now we have nearly
half a dozen, with the same worthiness issue between themselves.
Either we keep it very simple, or we make it very flexible. The former

would argue in favor of removing some of the existing formats, the
later
would let this new format in.


Nicolas
--
Sent from my mobile phone. Please excuse brevity and lack of formatting.

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