On Fri, Mar 18, 2016 at 05:11:54AM +0100, Mike Galbraith wrote: > On Thu, 2016-03-17 at 10:52 +0100, Peter Zijlstra wrote: > > > Andreas; Borislav said to Cc you since you wrote all this. > > The issue is that Linux assumes: > > > > > nr_logical_cpus = nr_cores * nr_siblings > > It also seems to now assume that if SMT is possible, it's enabled.
Urgh.. What I think, with my pre wakeup brain, happens is that the CPUID topology muck still reports 2 siblings (it tends to do that). But the BIOS only reports APIC-IDs for all your cores, so our nr_cpu_ids is reduced, while the nr_siblings count it not. And them *boom*. This is the same old problem that is nearly impossible to tell if HT is enabled or not -- complete and utter trainwreck :/ I need to go make wake-up-juice and ponder wth to do about this.
