linux-kernel - Re: [RFC PATCH v2 0/4] Add support for LZ4-compressed kernel

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Date:	Tue, 26 Feb 2013 15:59:56 -0500 (EST)
From:	Nicolas Pitre <nico@...xnic.net>
To:	"Markus F.X.J. Oberhumer" <markus@...rhumer.com>
Cc:	Kyungsik Lee <kyungsik.lee@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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,
	celinux-dev@...ts.celinuxforum.org,
	Nitin Gupta <nitingupta910@...il.com>,
	Richard Purdie <rpurdie@...nedhand.com>,
	Josh Triplett <josh@...htriplett.org>,
	Joe Millenbach <jmillenbach@...il.com>,
	David Sterba <dsterba@...e.cz>,
	Richard Cochran <richardcochran@...il.com>,
	Albin Tonnerre <albin.tonnerre@...e-electrons.com>,
	Egon Alter <egon.alter@....net>, hyojun.im@....com,
	chan.jeong@....com, raphael.andy.lee@...il.com
Subject: Re: [RFC PATCH v2 0/4] Add support for LZ4-compressed kernel

On Tue, 26 Feb 2013, Markus F.X.J. Oberhumer wrote:

> On 2013-02-26 07:24, Kyungsik Lee wrote:
> > Hi,
> > 
> > [...]
> > 
> > Through the benchmark, it was found that -Os Compiler flag for
> > decompress.o brought better decompression performance in most of cases
> > (ex, different compiler and hardware spec.) in ARM architecture.
> > 
> > Lastly, CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS is not always the best
> > option even though it is supported. The decompression speed can be
> > slightly slower in some cases.
> > 
> > This patchset is based on 3.8.
> > 
> > Any comments are appreciated.
> 
> Did you actually *try* the new LZO version and the patch (which is attached
> once again) as explained in https://lkml.org/lkml/2013/2/3/367 ?
> 
> Because the new LZO version is faster than LZ4 in my testing, at least
> when comparing apples with apples and enabling unaligned access in
> BOTH versions:
> 
> armv7 (Cortex-A9), Linaro gcc-4.6 -O3, Silesia test corpus, 256 kB block-size:
> 
>                    compression speed   decompression speed
> 
>   LZO-2012    :          44 MB/sec          117 MB/sec     no unaligned access
>   LZO-2013-UA :          47 MB/sec          167 MB/sec     Unaligned Access
>   LZ4 r88  UA :          46 MB/sec          154 MB/sec     Unaligned Access

To be fair, you should also take into account the compressed size of a 
typical ARM kernel.  Sometimes a slightly slower decompressor may be 
faster overall if the compressed image to work on is smaller.


Nicolas
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