Re: Linux-asm (was A patch for linux 2.1.127)

Rik van Riel (H.H.vanRiel@phys.uu.nl)
Mon, 16 Nov 1998 22:05:53 +0100 (CET)


On Mon, 16 Nov 1998, Jamie Lokier wrote:
> On Sun, Nov 15, 1998 at 10:25:37AM -0500, Richard B. Johnson wrote:
> > The demonstration code was an example of how to pipeline
> > something that is, buy it's nature, capable of being
> > pipelined. It is not a fix for something that is not
> > broken.
>
> If you want pipelining, why not help the GCC folks implement better
> instruction scheduling? One guy is claiming speedups of 30% or more
> just from better experimental scheduling for an AMD K6.

Things like writing 'unrolled loop' code and making sure
there are multiple things to be done at once (making good
multi-pipelining possible) are also nice things to do.

But I agree that we really should be working on gcc/egcs
to:
- add machine descriptions for AMD/Rise/Cyrix/Centaur/etc.
so the compiler can choose the proper instructions on the
proper chip (different cost for operands on different chips)
- have the compiler do more efficient multipipelining, this
will be especially useful for the Rise chip
- replace one expensive opcode by multiple (parallelizible)
cheap ones when useful (-frisc for pgcc???)
- make egcs do better instruction scheduling by avoiding
unneeded branches and/or doing predicative branching
(a'la Merced) in software (if it's worth it at all:-)

Rik -- slowly getting used to dvorak kbd layout...
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