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

[H. Peter Anvin]

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@xxxxxxxxxxx> wrote:

>On Mon, 28 Jan 2013, Andrew Morton wrote:
>
>> On Sat, 26 Jan 2013 14:50:43 +0900
>> Kyungsik Lee <kyungsik.lee@xxxxxxx> 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

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