Messages in this thread | | | Date | Tue, 23 Jul 2002 18:25:19 -0400 (EDT) | From | Bill Davidsen <> | Subject | RE: Wrong CPU count |
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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.
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