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>>>> + int cpu; >>>> + >>>> + cpumask_copy(&cpus, cpu_online_mask); >>>> + for_each_cpu(cpu, &cpus) { >>>> + cpumask_set_cpu(cpu, cpulist); >>>> + cpumask_andnot(&cpus, &cpus, cpu_smt_mask(cpu)); >>>> + } >>>> +} >>> >>> Don't we have a primary thread mask already? I thought we did. >> >> If you are referring to cpu_primary_thread_mask(), the CPUs are set on it >> based on the LSB of APICID, specifically: >> >> !(apicid & (__max_threads_per_core - 1)) >> >> It can so happen, the primary thread ((apicid & 1) == 0) of the core is >> offline while the secondary thread ((apicid & 1) == 1) is online but the >> traversal of (cpu_primary_thread_mask() & cpu_online_mask()) will simply >> skip these cores. >> >> Is there an equivalent mask that sets the first online CPU of each core? > > No I don't think we have that sitting around. > > But, stepping back, why is this even necessary? Is it just saving a few > IPIs in the super rare case that someone has offlined the primary thread > but not a secondary one? > > Why bother? Because, setting RMPOPT_BASE MSR (which is a per-core MSR) and RMPOPT instruction need to be issued on only one thread per core. If the primary thread is offlined and secondary thread is not considered, we will miss/skip setting either the RMPOPT_BASE MSR or not issuing the RMPOPT instruction for that physical CPU, which means no RMP optimizations enabled for that physical CPU. Thanks, Ashish