linux-kernel - Re: [PATCH 00/36] AArch64 Linux kernel port

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Date:	Thu, 12 Jul 2012 11:38:08 +0930
From:	Rusty Russell <rusty@...abs.org>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Arnd Bergmann <arnd@...db.de>, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ingo Molnar <mingo@...nel.org>,
	Olof Johansson <olof@...om.net>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Russell King <linux@....linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 00/36] AArch64 Linux kernel port

On Wed, 11 Jul 2012 11:53:35 +0100, Catalin Marinas <catalin.marinas@....com> wrote:
> Hi Rusty,

Hi Catalin,

        This is fun!

> On Wed, Jul 11, 2012 at 06:26:49AM +0100, Rusty Russell wrote:
> > I know it's a crazy idea, but why don't we try some actual analysis?
> 
> This kind of analysis is not relevant. It's not like you can use a tool
> to just mix the lines from one file with another and get a merged port.

Whether a tool or human would do it, using some methodology to measure
similarity of two ports seems more informative than relying on the gut
feel of developers.

> The tool claims unicore32 shares 57% with arch/arm. It gets confused in
> the same way because unicore32 started with the ARM port as the code
> base. Do we want it merged with arch/arm based on hashmatch?

It doesn't "get confused"; it means exactly what it says.  Sure, it's
rough, but it's unbiased.

And it indicates that arch/aarch64 is as related to arch/arm as
arch/unicore32 is, ie. no more than expected from an arm-derived port.
(I actually get 56% for unicore32, 52% for aarch64).

Thus I consider my previous position proven incorrect: aarch64 should be
its own tree.

> This tool also shows that pretty much most of the atomic.h file in
> AArch64 is the same with AArch32. That's completely wrong as the
> assembly syntax is different for the two architectures (even the asm
> comment has changed from @ to //). That's a file that can never be
> shared.

That's why I subtracted a randomly-chosen other arch (sparc) to try to
eliminate such boilerplate similarities.

Cheers,
Rusty.
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