Re: It's 1997. Do you know where your scheduler is?

> which release of gcc,


It really doesn't matter. Here are some Pentium cycle counts for the
same hand-scheduled 256-point complex FFT code:


      23085 (best) gcc 2.7.2.1 -O1 -fo-f-p
      41913 gcc 2.7.2.1 -O6 -fo-f-p
      47258 egcs 1.00 -O6 -fo-f-p -mpentiumpro
      56383 egcs 1.00 -O6 -fo-f-p -mpentium
      56860 (worst) egcs 1.00 -O6 -fo-f-p


I wonder what percentage of today's typical Pentium is wasted by bad
instruction scheduling, given that so many programmers rely on the C
compiler for optimization. Intel's compiler is allegedly not too
incompetent, but how many programs are actually compiled with it?


> which release of Pentium.


``Pentium'' refers to a specific chip design. All Pentium releases
use the same number of cycles for in-cache operations.


The Pentium Pro, as you noted, is a very different chip. Scheduling
code badly for the Pentium Pro would take quite a bit of effort.


Apparently the Pentium MMX is similar to a Pentium for optimization
purposes, and the Pentium II is just like a Pentium Pro; except, of
course, for the extra instructions and larger L1 caches.


---Dan
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