John McKown wrote:
>But, are there any z990 enhancements in the gcc compiler? If not, then
>recompiling will do not good.
Recent GCC versions support the -mtune and -march options to select
which machine to generate code for. See the GCC info page for full
documentation; the most important variants are probably:
-march=z990 Generate code that makes use of all new architecture
features provided with z990
-mtune=z990 Generate code optimized for z990 that will still run
on older processors
The effect of these flags will be:
- Make use of new instructions (the 'long displacement facility').
These instructions allow using immediate displacements > 4k,
which is particularly helpful with code that frequently accesses
objects (or stack frames) larger than 4kb.
(This is enabled with -march=z990 only.)
- Schedule instruction sequences so as to allow the processor to
make optimal use of the z990 superscalar instruction pipeline
that can execute up to three instructions in parallel (*if* they
are in the proper sequence).
(This is enabled with -mtune=z990 and -march=z990.)
These features are supported by GCC version 3.4 and above; SUSE
also has these features backported to their variant of GCC 3.3
(provided as system compiler with SLES9 and as optional extra
compiler with SLES8 SP3).
Note that the benefit you will see from optimizing code for z990
depends heavily on the particular code in question: there may be
no speed-up visible at all, but you may in some cases see performance
improvements of 5% or more.
Mit freundlichen Gruessen / Best Regards
Ulrich Weigand
--
Dr. Ulrich Weigand
Linux for S/390 Design & Development
IBM Deutschland Entwicklung GmbH, Schoenaicher Str. 220, 71032 Boeblingen
Phone: +49-7031/16-3727 --- Email: [EMAIL PROTECTED]
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