On Fri, 19 Jul 2002, Richard B. Johnson wrote:
> On Fri, 19 Jul 2002 venom@sns.it wrote:
>
> >
> > yes, as bios option.
> >
> > On my point of view it would be interesting to verify is hyperthreading is
> > really usefull or not.
> >
>
> It would be interesting to determine if "hyperthreading" in the CPU
> actually exists. It may just be an artifact of dual instruction units,
> actually a defect (perhaps harmless), that is hyped as a feature.
Clearly not, it requires another set of registers including instruction
counter.
> For instance, it has long been known that if a CPU were to have as
> many instruction units as possible instruction branches, program
> jumps upon logical conditions would not slow the machine down. The
> hardware just continues using the instruction unit that contains the
> correct program-flow while the others are re-loaded.
That is not correct, it certainly can slow the machine down. Speculative
execution is used, but it's not free, since it requires fetching
instructions not used through a limited bandwidth to memory. Much on this
in comp.arch, there is a tradeoff between avoiding stalls and causing
them, separate branch target cache, etc. Details probably a lot better to
be discussed there.
-- bill davidsen <davidsen@tmr.com> CTO, TMR Associates, Inc Doing interesting things with little computers since 1979.- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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