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Re: The new scheduler and x86 CPUs
- To: Vladimir Makarov <vmakarov at toke dot toronto dot redhat dot com>
- Subject: Re: The new scheduler and x86 CPUs
- From: Bernd Schmidt <bernds at redhat dot com>
- Date: Tue, 28 Aug 2001 22:12:44 +0100 (BST)
- cc: <jh at suse dot cz>, <gcc at gcc dot gnu dot org>
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
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.