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

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Date:	Fri, 01 Feb 2013 17:15:00 +0900
From:	"kyungsik.lee" <kyungsik.lee@....com>
To:	Egon Alter <egon.alter@....net>
CC:	linux-arm-kernel@...ts.infradead.org,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Marek <mmarek@...e.cz>, hyojun.im@....com,
	raphael.andy.lee@...il.com, linux-kbuild@...r.kernel.org,
	gunho.lee@....com, namhyung.kim@....com, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Josh Triplett <josh@...htriplett.org>,
	Nitin Gupta <nitingupta910@...il.com>,
	Richard Purdie <rpurdie@...nedhand.com>,
	Ingo Molnar <mingo@...hat.com>,
	Joe Millenbach <jmillenbach@...il.com>, chan.jeong@....com,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Albin Tonnerre <albin.tonnerre@...e-electrons.com>,
	CE Linux Developers List <celinux-dev@...ts.celinuxforum.org>,
	minchan.kim@....com
Subject: Re: [RFC PATCH 0/4] Add support for LZ4-compressed kernels

On 2013-01-29 오후 8:43, Egon Alter wrote:
> Am Dienstag, 29. Januar 2013, 10:15:49 schrieb Russell King - ARM Linux:
>> On Mon, Jan 28, 2013 at 02:25:10PM -0800, Andrew Morton wrote:
>>> 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?
>> Well... when I saw this my immediate reaction was "oh no, yet another
>> decompressor for the kernel".  We have five of these things already.
>> Do we really need a sixth?
>>
>> My feeling is that we should have:
>> - one decompressor which is the fastest
>> - one decompressor for the highest compression ratio
>> - one popular decompressor (eg conventional gzip)
> the problem gets more complicated as the "fastest" decompressor usually
> creates larger images which need more time to load from the storage, e.g. a
> one MB larger image on a 10 MB/s storage (note: bootloaders often configure
> the  storage controllers in slow modes) gives 100 ms more boot time, thus
> eating the gain of a "fast decompressor".
Yes, the larger image could matter. Definitely it takes longer.

Here are some updated test cases: Including "loading time"

                                 lzo           lz4
loading time:             480ms       510ms
decompression time: 336ms       180ms(with efficient unaligned memory 
access enabled and ARM optimization)
total time:                 816ms        690ms

lz4 is still 15% faster in total time. This one is similar to the 
simulated result by Russell King.

Thanks,
Kyungsik
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