your summary of hyperthreading is basically right. In 2011, the K8/K10 we were using did not have hyperthreading.
Most HPC sites, including LANL, where I worked, tended to turn hyperthreading off, as it was at best a mixed blessing. I note that many cloud providers have turned it off, for security reasons. There are HPC researchers out there planning to use hyperthreading, BUT: intel has announced that hyperthreading has no future in its chips: https://www.pcworld.com/article/2480487/hyperthreading-is-dead-in-intels-new-core-ultra-pc-chips.html#:~:text=Yes%2C%20hyperthreading%20has%20been%20banned,the%20feature%20from%20Lunar%20Lake . I was never a fan, and we did not make allowance for hyperthreading in NIX. On Tue, Feb 18, 2025 at 4:15 AM <tlaro...@kergis.com> wrote: > My knowledge being limited in this area, I guess that when x86 > announces, say, 8 cores / 16 threads, the two threads by core are > handled using superscalar (possibly pipelining): instead of executing > in parallel multiple instructions of one program, they allow to execute > in parallel multiple instructions of two distinct programs? > > But there are differences between physical cores and logical ones > (hardware threads): the local APIC table is uniq to the physical core. > > This does mean that the NIX approach will handle physical cores, and > that a kernel allocated to some physical core will be perhaps able to > use (in this case) two logical cores (hardware threads)? > > -- > Thierry Laronde <tlaronde +AT+ kergis +dot+ com> > http://www.kergis.com/ > http://kertex.kergis.com/ > Key fingerprint = 0FF7 E906 FBAF FE95 FD89 250D 52B1 AE95 6006 F40C ------------------------------------------ 9fans: 9fans Permalink: https://9fans.topicbox.com/groups/9fans/Tc2b75db61025b254-M1c21bf5026029ef8085278cc Delivery options: https://9fans.topicbox.com/groups/9fans/subscription
