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

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Date:	Tue, 29 Jan 2013 10:15:49 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Kyungsik Lee <kyungsik.lee@....com>,
	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 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)

And if we have a replacement one for one of these, then it should do
exactly that: replace it.  I realise that various architectures will
behave differently, so we should really be looking at numbers across
several arches.

Otherwise, where do we stop adding new ones?  After we have 6 of these
(which is after this one).  After 12?  After the 20th?
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