[Info-vax] Dvorak on Itanic

[Christopher]

> [3]http://web.archive.org/web/20010602154126/www.alphapowered.com/presen...

Many of the arguments in this article are hooey.

"Commercial programs have very low instruction-level parallelism, but
they are typically explicitly
multithreaded. Each thread is very sequential and includes long delays
waiting for
memory. The IA64 strategy of searching for instruction-level
parallelism cannot find the
orders of magnitude improvements available to Alpha through
simultaneous
multithreading."

IA-64 processors are completely capable of explicit multi-threading.
In addition, "automatic" threading is extremely hit and miss.  The
processor should not be involved in decisions about what to
multithread because it HAS NO CONTEXT.

They also mention out-of-order execution and dynamic instruction
parallelism.  Both of these techniques have their own costs.  During
speculative execution requests are made that *hopefully* will prove
out.  When they don't they are extremely expensive.

Consider too, all that dynamic speculation hardware takes both power
and space.  For architectures which have no, or have little,
instruction set support for static speculation hinting it has some
value.  However, if you can dedicate all of your silicon to actually
DOING THE WORK, that is much better.