On Sat, Jun 08, 2024 at 03:58:30PM +0200, Andreas Kähäri wrote:
> On Sat, Jun 08, 2024 at 11:39:28AM +0100, Kirill A. Korinsky wrote:
> > On Sat, 08 Jun 2024 11:09:29 +0100,
> > Omar Polo <o...@omarpolo.com> wrote:
> > >
> > > On 2024/06/08 10:09:07 +0100, Kirill A. Korinsky <kir...@korins.ky> wrote:
> > > > On Sat, 08 Jun 2024 04:57:49 +0100,
> > > > Gustavo Rios <rios.gust...@gmail.com> wrote:
> > > > >
> > > > > i have installed obsd on my dell notebook 8 cores processor. When i
> > > > > execute
> > > > > the top utility, it is showed the cores, from 0 (cpu0) to 7 (cpu7),
> > > > > but
> > > > > cpu1 and cpu3 is not listed. What is the problem ?
> > > > >
> > > >
> > > > A blind guess: sysctl hw.smt=1 may return your hypertreading cores.
> > >
> > > which is a very bad advice to give. There's a reason sysctl hw.smt=1
> > > defaults to that value. One should rather give a "blind guess" of "your
> > > hyperthread cores are disabled by default" rather than give a bad advice
> > > without explanation.
> >
> > I'll make my advice cleaner, I defently mean that missed cores probably is
> > disabled becuae it is hyperthreading ones which can be seen as offline in
> > htop, or enable via sysctl.
>
>
> Not knowing too much about these things, I think it looks a bit strange
> that *two* out of eight CPUs are disabled due to hypethreading. I would
> have expected every second one be disabled, i.e., four out of eight.
This simple rule does not apply to more modern CPUs, which can have
different types of cores, some with hyperthreading and some without.
-Otto
>
>
>
> >
> > Also, I'd like to add that from security point of view SMT in general and
> > hyperthreading as an example is very bad idea.
> >
> > Thus, here old but interesting results that enabling hyperthreading has
> > negative effect on performance of have CPU used applications:
> > https://web.archive.org/web/20220325090914/http://users.telenet.be/nicvroom/performanceP4.htm
> >
> > --
> > wbr, Kirill
>
> --
> Andreas (Kusalananda) Kähäri
> SciLifeLab, NBIS, ICM
> Uppsala University, Sweden
>
> .
>
