Re: [patch] Disable old loop optimizer

[Daniel Jacobowitz <drow at false dot org>]

On Wed, Apr 13, 2005 at 01:17:35PM -0400, Paul Schlie wrote:
> - if you're referring to the count also being used as an array index into
>   memory; I agree that since it affects the memory access sequence it may
>   affect cache efficiency, but only if the array is only partially cached,
>   as if it's either already fully cached, or not cashed at all, it shouldn't
>   have any effect (as you'll either always get a cache hit, or a cache miss
>   upon entry to each newly addressed cache line; but understand that upon a
>   miss, if the cache controller isn't sensitive to the location of the miss
>   within the cache line/block, it may not optimally fill from the most
>   optimal end first, thereby increasing the latency to access the requested
>   datum; but that would seem to be an inadequacy of the cache controller as
>   opposed to anything else, and very target/cache controller specific so not
>   sure how or even if it should effect this type of optimization in
>   general? Maybe there should be a target switch to enable an incrementing
>   or decrementing sequential memory access bias which can influence such
>   optimization choices?)

It sounds like you need to do some research on how modern
non-microcontroller architectures manage their caches.  Automatic
prefetching is more sophisticated than this.  I'm confident there are
at least several architectures that handle sequential-forward memory
access better than sequential-backward.

-- 
Daniel Jacobowitz
CodeSourcery, LLC