Re: Hyper-Threading Vulnerability

[Arjan van de Ven <arjan@infradead.org>]

On Sat, 2005-05-14 at 19:40 -0400, Lee Revell wrote:
> > it's a matter of time (my estimate is a year or two) before processors
> > get variable frequencies based on temperature targets etc...
> > and then rdtsc is really useless for this kind of thing..
> 
> I was under the impression that P4 and later processors do not vary the
> TSC rate when doing frequency scaling.  This is mentioned in the
> documentation for the high res timers patch.

seems not the case, and worse, during idle time the clock is allowed to
stop entirely.... (and that is also happening more and more and linux is
getting more agressive idle support (eg no timer tick and such patches)
which will trigger bios thresholds for this even more too.



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