Re: [RFC PATCH 2/3 v3] perf: Implement Nehalem uncore pmu

[Andi Kleen]

> If think there you want something like:
> 
> if (cpu == cpumask_first(topology_core_siblings(cpu)) {
>       rdmsrl(MSR_IA32_DEBUGCTLMSR, val);
>      wrmsrl(MSR_IA32_DEBUGCTLMSR, val | DEBUGCTLMSR_ENABLE_UNCORE_PMI);
> }

You have to be careful with hotplug. The code would need to be rerun
on hotplug. Otherwise the interrupt may end up on a downed CPU.
-Andi
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