linux-kernel - Re: [Fastboot] [RFC] ELF Relocatable x86 and x86

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Message-ID: <44D1815C.1040508@zytor.com>
Date:	Wed, 02 Aug 2006 21:53:48 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Don Zickus <dzickus@...hat.com>, fastboot@...l.org,
	Horms <horms@...ge.net.au>,
	Jan Kratochvil <lace@...kratochvil.net>,
	Magnus Damm <magnus.damm@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [Fastboot] [RFC] ELF Relocatable x86 and x86_64 bzImages

Eric W. Biederman wrote:
> Don Zickus <dzickus@...hat.com> writes:
> 
>>> There is one outstanding issue where I am probably requiring too much
>> alignment
>>> on the arch/i386 kernel.  
>> There was posts awhile ago about optimizing the kernel performance by
>> loading it at a 4MB offset.  
>>
>> http://www.lkml.org/lkml/2006/2/23/189
>>
>> Your changes breaks that on i386 (not aligned on a 4MB boundary).  But a
>> 5MB offset works.  Is that the correct update or does that break the
>> original idea?
> 
> That patch should still apply and work as described.
> 
> Actually when this stuipd cold I have stops slowing me down,
> and I fix the alignment to what it really needs to be ~= 8KB.
> 
> Then bootloaders should be able to make the decision.
> 
> HPA Does that sound at all interesting?
> 

I'm sorry, it's not clear to me what you're asking here.

The bootloaders will load bzImage at the 1 MB point, and it's up to the 
decompressor to locate it appropriately.  It has (correctly) been 
pointed out that it would be faster if the decompressed kernel is 
located to the 4 MB point -- large pages don't work below 2/4 MB due to 
interference with the fixed MTRRs -- but that's doesn't affect the boot 
protocol in any way.

I was under the impression that your relocatable patches allows the boot 
loader to load the bzImage at a different address than the usual 
0x100000; but again, that shouldn't affect the kernel's final resting place.

	-hpa

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