[nzlug] Kernel squared

[Michal Ludvig]

Daniel Pittman wrote:
> "Phillip Hutchings" <sitharus at sitharus.com> writes:
>> How about running an VIA EPIA CPU. They have a small cache and don't
>> implement all of the i686 instruction set.
> 
> They don't implement an *optional* portion of the i686 instruction set
> as documented.  Intel did choose to implement them[1] leading to the
> mistaken belief that VIA had an incomplete system.

It was certainly a bad decision from VIA. However recent VIA CPUs
already have full i686 instruction set. Definitely true for core
Nehemiah and newer, perhaps for some older as well. And Nehemiah was out
some ... two years ago? Maybe three?

>> You do notice performance increases if you target this CPU rather than
>> sticking with 386 packages.
> 
> I wasn't aware of that.  Where do the VIA EPIA systems benefit?
> 
> Is it instruction scheduling, cache awareness, alignment, or something
> else?

Cryptography. OpenSSL optimized for these CPUs is NNN-times faster ;-)

> What sort of performance gain are we talking about; have you some
> performance numbers to show the gains you see there?

http://www.logix.cz/michal/devel/padlock/bench.xp (not yet updated with
VIA Esther results for SHA1/SHA256).

Indeed, that's a somewhat specific usecase and it's disputable to call
it "optimization" afterall ;-)

Michal