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

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Date:	Wed, 30 Jan 2013 11:23:53 +0100
From:	Johannes Stezenbach <js@...21.net>
To:	Nicolas Pitre <nico@...xnic.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Kyungsik Lee <kyungsik.lee@....com>,
	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>,
	"Markus F.X.J. Oberhumer" <markus@...rhumer.com>
Subject: Re: [RFC PATCH 0/4] Add support for LZ4-compressed kernels

On Mon, Jan 28, 2013 at 11:29:14PM -0500, Nicolas Pitre 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)
> > 
> > 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.

This reminded me to check the status of the lzo update and it
seems it got lost?
http://lkml.org/lkml/2012/10/3/144

(Cc: added, I hope Markus still cares and someone could
eventually take his patch once he resends it.)

Johannes
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