On Wed, Feb 19, 2025 at 12:17:48PM -0800, ron minnich wrote: > 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. >
Thanks for the explanations! We are back to what you wrote about the network and distributed computing (in your paper about the Linux implementation of the 9P protocol), but on the micro-level this time: this hyperthreading seems also like a patchwork applied afterwards, mimicking in hardware what was done (with notorious unfelicities) in software. (And the huge x86 ISA is a memorial to all the dead-ends that have been attempted; one more grave in the cemetery). > > 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 -- 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-M1bf647f44917f3434e19895b Delivery options: https://9fans.topicbox.com/groups/9fans/subscription
