Linus Torvalds (torvalds@linux-foundation.org) on 9/28/09 wrote:
---------------------------
>no thanks (no@thanks.com) on 9/27/09 wrote:
>>
>>Does this line of thinking extend so that you now think
>>doing Transmeta style translation machines are the wrong
>>thing to do?
>
>One of the things that my experiences at Transmeta convinced
>me of is that doing in-order translation machines is
>the wrong thing to do.
>
>>That is, should OOO be only done in hardware rather than
>>runtime software on an in-order uarch?
>
>I think Transmeta did many things really well, and was
>fairly good at capturing some "big pattern" dynamic behavior
>and optimizing that at runtime with software. We did some
>clever things, and I suspect JIT's with more degrees of
>freedom (eg Java) can do even more.
>
>But there is absolutely nothing you can do in software for
>dynamic behavior that is on the scale of tens (or even
>thousands) of cycles. Cache access patterns need OoO (or
>at least some weaker form of it - maybe somebody makes a
>good run-ahead engine).
>
>Instruction scheduling likewise is about dynamic behavior
>at a low level where software can't do the last details.
>The compiler (static or dynamic) may do fine for linear
>basic blocks without lots of cache behavior, and you can
>extend those basic blocks with various tricks (predication,
>unrolling, inlining), but most of those tricks have fairly
>serious limitations and downsides to them. And none of them
>make the problem go away in the end.
>
>So I think JIT compiling is great. But in the end, you
>still need dynamic hardware in addition to all the
>things you can do in software.
>
>Linus

Well, I could write what I think about the matters you mentioned - but since Potatoswatter in an other forum thread clearly indicated that I am just pointlessly making stuff up or, even better, stealing ideas - I am not going to bother writing what I think.