On Tue Jan 6, 2026 at 3:04 AM UTC, Mike Larkin wrote: > According to a quick google search, these CPUs expose their topology (right or > wrong) as SMT based on AMD's "CMT" (See cut-paste below). > > We use the CPU's own reported topology as reported by CPUID when making the > decision if something is SMT or not. > > HTH. > > -ml > > > ------ > > The appearance of SMT (Simultaneous Multithreading) in the CPUID topology for > an AMD Opteron 4256 EE is a result of the Bulldozer architecture (Valencia) > design and how operating systems interpret its CMT (Clustered Multi-Thread) > structure. > > Why SMT is Reported: > > Module-Based Architecture: The Opteron 4256 EE is built on 4 Bulldozer > modules, > each containing two integer cores that share certain components, such as the > L2 cache and FPU. > > CPUID Interpretation: To ensure compatibility with Windows and Linux > schedulers, > AMD processors of this era often export a topology that mimics SMT. The OS > sees > two "logical cores" per module; because they share resources, the system > reports > this relationship as a thread-level (SMT) grouping rather than independent > physical cores.
Hi Mike, That's interesting. Thank you for sharing! I didn't realize there were security concerns there. I guess it's not an issue with Lisbon? (4100 series) Would anyone happen to know if Piledriver (3300+4300+6300 series) is designed in the same manner as Bulldozer? Sounds like this isn't a bug at all. Just didn't match all of the documentation I found on the processor. -Henrich
