linux-kernel - Re: [PATCH V6 07/13] perf: Generic pci uncore device support

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Date:	Fri, 15 Jun 2012 18:02:53 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	"Yan, Zheng" <zheng.z.yan@...el.com>
Cc:	mingo@...e.hu, jolsa@...hat.com, eranian@...gle.com,
	andi@...stfloor.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V6 07/13] perf: Generic pci uncore device support

On Fri, 2012-06-15 at 14:31 +0800, Yan, Zheng wrote:
> @@ -305,6 +310,22 @@ struct intel_uncore_box *uncore_alloc_box(int cpu)
>  static struct intel_uncore_box *
>  uncore_pmu_to_box(struct intel_uncore_pmu *pmu, int cpu)
>  {
> +       static struct intel_uncore_box *box;
> +
> +       box =  *per_cpu_ptr(pmu->box, cpu);
> +       if (box)
> +               return box;
> +
> +       raw_spin_lock(&uncore_box_lock);
> +       list_for_each_entry(box, &pmu->box_list, list) {
> +               if (box->phys_id == topology_physical_package_id(cpu)) {
> +                       atomic_inc(&box->refcnt);
> +                       *per_cpu_ptr(pmu->box, cpu) = box;
> +                       break;
> +               }
> +       }
> +       raw_spin_unlock(&uncore_box_lock);
> +
>         return *per_cpu_ptr(pmu->box, cpu);
>  } 

So why can't we do that lookup from a hotplug notifier?
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