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

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Date:	Mon, 28 Jan 2013 22:18:04 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Nicolas Pitre <nico@...xnic.net>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	Kyungsik Lee <kyungsik.lee@....com>,
	Russell King <linux@....linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.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

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@...xnic.net> wrote:

>On Mon, 28 Jan 2013, Andrew Morton wrote:
>
>> 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?
>
>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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