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    SubjectRe: latest linus-2.5 BK broken
    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...

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