Re: kernel optimization

[Alan Cox]

On Sad, 2005-07-23 at 02:30 -0400, cutaway@xxxxxxxxxxxxx wrote:
> Larger does not always mean slower.  If it did, nobody would implement a
> loop unrolling optimization.

Generally speaking nowdays it does. Almost all loop unrolls are a loss
on PIV.

> ex. Look at how GCC generates jump tables for switch() when there's about
> 10-12 (or more) case's sparsely scattered in the rage from 0 through 255.

You are comparing with very expensive jump operations its an unusual
case. For the majority of situations the TLB/cache overhead of misses
vastly outweighs the odd clock cycle gained by verbose output.


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