linux-kernel - Re: [PATCH 01/14] x86, boot: align the .bss section in the decompressor

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Date:	Fri, 08 May 2009 09:54:41 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
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, mingo@...e.hu,
	tglx@...utronix.de, ebiederm@...ssion.com
Subject: Re: [PATCH 01/14] x86, boot: align the .bss section in the decompressor

Sam Ravnborg wrote:
>>  	}
>> +	. = ALIGN(32);
> 
> Where does this magic 32 comes from?
> I would assume the better choice would be:
> 	. = ALIGN(L1_CACHE_BYTES);
> 
> So we match the relevant CPU.
> 
> In general for alignmnet of output sections I see the need for:
> 1) Function call
> 2) L1_CACHE_BYTES
> 3) PAGE_SIZE
> 4) 2*PAGE_SIZE
> 
> But I see magic constant used here and there that does not match
> the above (when looking at all archs).
> So I act when I see a new 'magic' number..
> 

I picked 32 as being larger than the maximum known size that affects rep
performance, but L1_CACHE_BYTES really would make more sense, you're right.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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