linux-kernel - Re: [PATCH 03/14] x86, config: change defaults PHYSICAL_START and PHYSICAL

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Message-ID: <20090508094726.GE3559@elte.hu>
Date:	Fri, 8 May 2009 11:47:26 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	linux-kernel@...r.kernel.org, vgoyal@...hat.com, hbabu@...ibm.com,
	kexec@...ts.infradead.org, ying.huang@...el.com,
	tglx@...utronix.de, ebiederm@...ssion.com,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 03/14] x86, config: change defaults PHYSICAL_START and
	PHYSICAL_ALIGN


* Sam Ravnborg <sam@...nborg.org> wrote:

> On Thu, May 07, 2009 at 03:26:51PM -0700, H. Peter Anvin wrote:
> > From: H. Peter Anvin <hpa@...or.com>
> > 
> > Change the default for CONFIG_PHYSICAL_START to 16 MB; 4 MB if
> > EMBEDDED.  Change the default for CONFIG_PHYSICAL_ALIGN to match up
> > with a large page alignment datum (4 MB for non-PAE, 2 MB for PAE.)
> > 
> > The default of 16 MB is designed to avoid occupying ZONE_DMA, as well
> > as avoiding a 15-16 MB memory hole, which some vendors inexplicably
> > still have in their systems.
> > 
> > [ Impact: minor performance improvement, leave ZONE_DMA free ]
> > 
> > Signed-off-by: H. Peter Anvin <hpa@...or.com>
> > ---
> >  arch/x86/Kconfig |   19 +++++++++++--------
> >  1 files changed, 11 insertions(+), 8 deletions(-)
> > 
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index 039c3f0..13b3a5a 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -1455,17 +1455,20 @@ config KEXEC_JUMP
> >  
> >  config PHYSICAL_START
> >  	hex "Physical address where the kernel is loaded" if (EMBEDDED || CRASH_DUMP)
> > -	default "0x1000000" if X86_NUMAQ
> > -	default "0x200000" if X86_64
> > -	default "0x100000"
> > +	default "0x400000" if EMBEDDED
> > +	default "0x1000000"
> >  	---help---
> >  	  This gives the physical address where the kernel is loaded.
> >  
> >  	  If kernel is a not relocatable (CONFIG_RELOCATABLE=n) then
> >  	  bzImage will decompress itself to above physical address and
> > -	  run from there. Otherwise, bzImage will run from the address where
> > -	  it has been loaded by the boot loader and will ignore above physical
> > -	  address.
> > +	  run from there. Otherwise, bzImage will run from the either
> > +	  the above physical address or where it has been loaded by
> > +	  the boot loader, whichever is higher.
> > +
> > +	  For embedded machines with very small memory (less than
> > +	  about 24 MB) this may need to be adjusted downward from the
> > +	  default value of 0x1000000 (16 MB).
> 
> But in the above you say that default is "0x400000" if EMBEDDED
> That is in contradiction with the help - no?

Yes, the help text is wrong.

	Ingo
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