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Date: Mon, 18 Jun 2012 11:06:03 +0800
From: "Yan, Zheng" <zheng.z.yan@intel.com>
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To: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: mingo@elte.hu, jolsa@redhat.com, eranian@google.com, andi@firstfloor.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH V6 07/13] perf: Generic pci uncore device support
References: <1339741902-8449-1-git-send-email-zheng.z.yan@intel.com>  <1339741902-8449-8-git-send-email-zheng.z.yan@intel.com> <1339776173.2559.77.camel@twins>
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On 06/16/2012 12:02 AM, Peter Zijlstra wrote:
> 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?
> 
We can. But I personally prefer not to mix pci uncore initialization
code with cpu hotplug notifier. Because pci hotplug and cpu hotplug
are separate process, I'm not completely sure which one happens first.

Regards
Yan, Zheng