Re: Dragonfly and Hyperthreading....

[Tom Hummel <tom@xxxxxxxxxxxxx>]

>     is that performance is extremely assymetric.  You could waste hundreds
>     of man hours writing an HT aware scheduler and still not have it work
>     well for all situations.

Microsoft implemented in a way that made many people happy, and HT had 
it's impact on the minds of many. There should be some reward, but i 
don't know what impact such implementation could have on the rest of the 
code. Could you give us some details?

>     Even more to the point, HT technology was most useful in past years
>     when instruction pipelines were not able to make full use of the cpu's
>     resources.  That has changed as well.  Today's cpu's instruction 
>     pipelines are able to utility a far higher percentage of the cpu's
>     available resources, making HT a lot less useful.  HT has only been
AFAIR Intel intentionally slowed down pipeline operations to the 
execution units, so they could push up the clock frequency, to show 
customers some really high numbers, and later (2004) they discovered 
netburst isn't going to go to 10Ghz, as they predicted in 2003.
I think this is an Intel specific mistake, but nonetheless makes SMT 
useless on cpus with well designed pipelines.

>     viable up till now because Intel's cpu architecture sucks rocks compared
>     with AMD's, but Intel can no longer compete by boosting clock rate so
>     now they are stuck... they have to slow their cpus down and make them
>     more efficient, and that will kill HT's effectiveness even if you 
>     ignore the heat issue.
Maybe HT will be the only way to gain more effectiveness with lower 
clock frequency on netburst (P4).
My point of interested is what's AMD making better?

. ..tom