linux-kernel - Re: [PATCH -queue v0 1/6] [loongson] add basic loongson-2f support

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Message-ID: <20091105084537.GA12582@linux-mips.org>
Date:	Thu, 5 Nov 2009 09:45:37 +0100
From:	Ralf Baechle <ralf@...ux-mips.org>
To:	Wu Zhangjin <wuzhangjin@...il.com>
Cc:	Arnaud Patard <apatard@...driva.com>, linux-mips@...ux-mips.org,
	LKML <linux-kernel@...r.kernel.org>, huhb@...ote.com,
	yanh@...ote.com, Zhang Le <r0bertz@...too.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nicholas Mc Guire <der.herr@...r.at>, zhangfx@...ote.com,
	liujl@...ote.com
Subject: Re: [PATCH -queue v0 1/6] [loongson] add basic loongson-2f support

On Thu, Nov 05, 2009 at 09:39:36AM +0800, Wu Zhangjin wrote:

> > > > We have other systems where 32-bit kernel support is just remarkably ugly.
> > > > We've dropped 32-bit support for the SGI IP32 aka O2 - nobody seems to even
> > > > have really noticed that.  The Sibyte systems would be good candidates to do
> > > > the same as accesses to outside the 32-bit address space are needed very
> > > > frequently.
> > > > 
> > > 
> > > So, we really remove the 32bit support?
> > > 
> > > 1312 config CPU_LOONGSON2
> > > 1313         bool
> > > 1314         select CPU_SUPPORTS_32BIT_KERNEL  --> remove it?
> > > 1315         select CPU_SUPPORTS_64BIT_KERNEL
> > > 1316         select CPU_SUPPORTS_HIGHMEM
> > > 
> > > If you all agree, I will send a new patch to remove the above line and
> > > resend the corresponding patches without 32bit support, and removed the
> > > relative CONFIG_64BIT lines in the patches too.
> > 
> > If you need highmem with 32-bit (and with Loongson systems I assume that
> > virtually all systems will have enough RAM to require that) then you're
> > almost certainly better off going 64-bit.  Highmem takes a performance toll
> > which for some workloads can be very significant.  And while highmem won't
> > go away any time soon it's nothing kernel performance is being tuned for,
> > so it's only going to get worse into the future so I'd not waste time on
> > highmem unless I have to.
> > 
> 
> What I have mentioned: "perhaps some guys need the 32bit version" here
> means, perhaps some embedded systems without enough memory and enough
> storage space may need the 32bit version, they not need highmem and
> also, the 32bit version will save some storage space for them. and I
> have used the 32bit version on my box and notebook(of course, only for
> experiments), no obvious problems.
> 
> Reserve the 32bit version as an choice and select 64bit by default in
> the default config file?

No problem - I was just expressing my expressing my experiences on the
usefulness of supporting both settings.  One usually tends up favored, the
other little used.

  Ralf
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