Re: [PATCH] flex_array: avoid divisions when accessing elements

[Dave Hansen]

On Mon, 2011-05-02 at 13:26 -0400, Eric Paris wrote:
> On most architectures division is an expensive operation and accessing an
> element currently requires four of them.  This performance penalty
> effectively precludes flex arrays from being used on any kind of fast
> path.  However, two of these divisions can be handled at creation time and
> the others can be replaced by a reciprocal divide, completely avoiding
> real divisions on access.
> 
> Signed-off-by: Jesse Gross <jesse@xxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Eric Paris <eparis@xxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> [rebase on top of changes to support 0 len elements: eparis]
> [initialize part_nr when array fits entirely in base: eparis]
> Signed-off-by: Eric Paris <eparis@xxxxxxxxxx> 

This seems sane to me, especially in the element access case.

Acked-by: Dave Hansen <dave@xxxxxxxxxxxxxxxxxx>

-- Dave

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