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

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Date:	Mon, 28 Jan 2013 14:25:10 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Kyungsik Lee <kyungsik.lee@....com>
Cc:	Russell King <linux@....linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Michal Marek <mmarek@...e.cz>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-kbuild@...r.kernel.org, x86@...nel.org,
	Nitin Gupta <nitingupta910@...il.com>,
	Richard Purdie <rpurdie@...nedhand.com>,
	Josh Triplett <josh@...htriplett.org>,
	Joe Millenbach <jmillenbach@...il.com>,
	Albin Tonnerre <albin.tonnerre@...e-electrons.com>,
	hyojun.im@....com, chan.jeong@....com, gunho.lee@....com,
	minchan.kim@....com, namhyung.kim@....com,
	raphael.andy.lee@...il.com,
	CE Linux Developers List <celinux-dev@...ts.celinuxforum.org>
Subject: Re: [RFC PATCH 0/4] Add support for LZ4-compressed kernels

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

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