linux-kernel - Re: [PATCH 22/37] move round

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Date:	Mon, 25 Jan 2010 16:58:10 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Yinghai Lu <yinghai@...nel.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH 22/37] move round_up/down to kernel.h

On 01/25/2010 04:40 PM, Andrew Morton wrote:
> 
> The problem is that arch/x86/include/asm/proto.h implements private
> rounding macros.  The right way to fix that is to convert each x86
> "call site" over to using the standard macros from kernel.h, then
> finally remove the private definitions from
> arch/x86/include/asm/proto.h.  Don't just copy them over to kernel.h
> and make things muddier than they already are!
> 
> If during that conversion it is found that the standard macros for some
> reason don't suit the x86 usage sites then please propose
> enhancements/fixes to the existing kernel.h facilities.
> 

They don't.

The kernel-global alignment macros assume that either the alignment
datum (divisor) is a constant, or that it is acceptable to take the hit
of a division.  Unfortunately, we have real use cases where the
alignment (guaranteed to be a power of two) is variable, but we don't
want to take the hit of a full-blown division.

I suspect the global kernel tree has those, too, but it would seem to be
a dramatic change to change to change the existing facilities to assume
power of two alignment...

	-hpa
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