FreeBSD Security Advisory FreeBSD-SA-05:09.htt [REVISED]

[Garrett Wollman]

<<On Sat, 14 May 2005 04:20:19 +0200, "Poul-Henning Kamp" <phk at phk.freebsd.dk> said:

> The political problem is that if all operating systems do that,
> Intel has a pretty dud feature on their hands, and they are not
> particularly eager to accept that fact.

Intel already had a pretty dud feature on their hands; just ask anyone
in the architecture community (probably including those who work for
Intel).  Pentium 4 CPUs simply don't have enough I/O bandwidth to
maintain two simultaneous, independent instruction streams.  The value
to the feature can't be realized until you have enough cache (in both
size and bandwidth) to be able to partition it among logical CPUs in
exactly the manner that Colin has suggested.  (The fundamental problem
in computer architecture for the past several years has been how to
deal with the fact that gates are cheap and easy to make, but wires --
particularly external I/O wires -- are expensive and hard.)

The only way to get full performance out of an HTT processor today is
for both threads to be running out of L1 cache.  Multimedia and
numerical benchmarks are often parallelizable in this way (assuming
the OS provides gang scheduling); general-purpose applications rarely
are.

-GAWollman