As per the comment below; due to BIOS it is sometimes impossible to know if there actually are smp siblings until the machine is fully enumerated.
Signed-off-by: Peter Zijlstra (Intel) <[email protected]> --- arch/x86/kernel/smpboot.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -312,8 +312,21 @@ static void __init smp_init_package_map( /* * Today neither Intel nor AMD support heterogenous systems. That * might change in the future.... + * + * While ideally we'd want '* smp_num_siblings' in the below @ncpus + * computation, this won't actually work since some Intel BIOSes + * report inconsistent HT data when they disable HT. + * + * In particular, they reduce the APIC-IDs to only include the cores, + * but leave the CPUID topology to say there are (2) siblings. + * This means we don't know how many threads there will be until + * after the APIC enumeration. + * + * By not including this we'll sometimes over-estimate the number of + * logical packages by the amount of !present siblings, but this is + * still better than MAX_LOCAL_APIC. */ - ncpus = boot_cpu_data.x86_max_cores * smp_num_siblings; + ncpus = boot_cpu_data.x86_max_cores; __max_logical_packages = DIV_ROUND_UP(nr_cpu_ids, ncpus); /*
