Re: latest linus-2.5 BK broken

Martin Dalecki
2002-06-20T21:59:25Z

Użytkownik Linus Torvalds napisał:
>
> On Thu, 20 Jun 2002, Martin Dalecki wrote:
>
>>Linus you forget one simple fact - a HT CPU is *not* two CPUs.
>>It is one CPU with a slightly better utilization of the
>>super scalar pipelines.
>
>
> Doesn't matter. It's SMP to software, _and_ it is a perfect example of how
> integration, in the form of almost free transistors, changes the
> economics.

Well but this simply still doesn't make SMP magically scale
better. HT gives you about 12% increase in throughput on average.
This will hardly increase your MP3 ripping expierence :-).

> Integration is _not_ "just another way".
>
> Integration fundamentally changes the whole equation.
>
> When you integrate the SMP capabilities on the CPU, suddenly the world
> changes, because suddenly SMP is cheap and easy to do for motherboard
> manufacturers that would never have done it before. Suddenly SMP is
> available at mass-market prices.

And suddenly the Chip-Set manufacturers start to buy CPU
designs like creazy, becouse they can see what will be next... of course.

> When you integrate multiple CPU's on one standard die (either HT or real
> CPU's), the same thing happens.

Again HT is still only one CPU. You are too software centric :-).

> When you start integrating crossbars etc "numa-like" stuff, like Hammer
> apparently is doing, you get the same old technology, but it _behaves_
> differently.

Yes HT gives 12%. naive SMP gives 50% and good SMP (aka corssbar bus)
gives 70% for two CPU. All those numbers are well below the level
where more then 2-4 makes hardly any sense... Amdahl bites you still if you
read it like:

88% waste (well actuall this time not)
50% waste
20% waste

on scale.

However corssbar switches are indeed allowing for maximally
64 CPUs and more importantly it's the first step since a long time
to provide better overall system throughput. However they will still
not be near any commodity - too much heat for the foreseeable future.

> You see this outside CPU's too.
>
> When people started integrating high-performance 3D onto a single die, the
> _market_ changed. The way people used it changed. It's largely the same
> technology that has been around for a long time in visual workstations,
> but it's DIFFERENT thanks to low prices and easy integration into
> bog-standard PC's.
>
> A 3D tech person might say that the technology is still the same.
>
> But a real human will notice that it's radically different.

Yes but you can drive the technology only up to the perceptual limits
of a human. For example since about 6 years all those advancements
in the graphics area are largely uninterresting to me. I don't
play computer games. Never - they are too boring. Jet another
fan in my computer - no thank's.

> Did you mention that there are a lot more resistors in computers than
> CPU's? No. It is irrelevant. It doesn't drive technology in fundamental
> ways - even though the amount of fundamental technolgy inherent on a
> modern motherboard in _just_ the passive components like the resistor
> network is way beyond what people built just a few years ago.

Well the last real technological jump comparable to the invention
of television was actually due to this kind of CPUs which you
compare to microbes - mobiles :-). And well I'm awaiting the
day where there will be some WinWLAN card as shoddy as those Win
modems are... Fortunately they made 802.11b complicated enough :-)
But with a corssbar switch in place they could well make up for
the latency on the main CPU... oh fear... oh scare...