Re: [PATCH 22/37] move round_up/down to kernel.h

From: H. Peter Anvin
Date: Mon Jan 25 2010 - 19:59:27 EST

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...

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