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Re: The new scheduler and x86 CPUs


On Tue, 28 Aug 2001, Vladimir Makarov wrote:

>   Actually I don't like out-of-order/speculative processors.  It is
> solution for pure people which can not afford to write a good compiler
> requiring huge investments.  It is a dead end approach.  The more
> registers and issue rate, the more percent of logic is needed for
> control of out-of-order, speculative execution.  Intel understood
> this.  They have a decent compiler and gcc is far behind it.  We
> should worry about this.

Look at the published SPEC numbers - even when using Intel's compiler,
Itanium is far away from being a top performer for integer programs.  I
don't think that's an accident; you have a lot more information available
at run-time than at compile-time.  One of the reasons that optimizing for
ia64 is so difficult is that you don't know enough about e.g. memory
aliasing.

Why is OOO a dead-end approach?  If there's parallelism to extract
in a program, then if a compiler can find it, an OOO core can find it
just as well.


Bernd


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