On Tue, Jun 14, 2005 at 04:27:55PM -0700, Christoph Lameter wrote:
> On Wed, 15 Jun 2005, Andi Kleen wrote:
>
> > > If these maps would start in the middle of a cacheline then additional
> > > cacheline fetches may become necessary to scan an array etc.
> >
> > But the CPUs do prefetching anyways for that. Do you have numbers
> > that this is actually worth it?
>
> Its not only for scanning an array. A struct may contains a lot of
> related information like for example boot_cpu_data. Aligning
> increases locality and the likelyhood that no additional cachelines have
> to be fetched.
On the other hand it will increase the overall working set so there might
be more cache misses again. It's a trade off and the outcome is not clear.
Do you have numbers?
When in doubt I would suggest the less wasteful in memory solution.
-Andi
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