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. > > 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 .
