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SubjectRe: [PATCH V2 16/25] perf/x86: Register hybrid PMUs
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On 3/11/2021 7:34 AM, Peter Zijlstra wrote:
> On Wed, Mar 10, 2021 at 08:37:52AM -0800, kan.liang@linux.intel.com wrote:
>> @@ -2092,9 +2105,37 @@ static int __init init_hw_perf_events(void)
>> if (err)
>> goto out1;
>>
>> - err = perf_pmu_register(&pmu, "cpu", PERF_TYPE_RAW);
>> - if (err)
>> - goto out2;
>> + if (!is_hybrid()) {
>> + err = perf_pmu_register(&pmu, "cpu", PERF_TYPE_RAW);
>> + if (err)
>> + goto out2;
>> + } else {
>> + u8 cpu_type = get_hybrid_cpu_type(smp_processor_id());
>> + struct x86_hybrid_pmu *hybrid_pmu;
>> + int i;
>> +
>> + for (i = 0; i < x86_pmu.num_hybrid_pmus; i++) {
>> + hybrid_pmu = &x86_pmu.hybrid_pmu[i];
>> +
>> + hybrid_pmu->pmu = pmu;
>> + hybrid_pmu->pmu.type = -1;
>> + hybrid_pmu->pmu.attr_update = x86_pmu.attr_update;
>> + hybrid_pmu->pmu.capabilities |= PERF_PMU_CAP_HETEROGENEOUS_CPUS;
>> +
>> + /* Only register the PMU for the boot CPU */
>
> Why ?!
> > AFAICT we could register them all here. That instantly fixes that
> CPU_STARTING / CPU_DEAD fail elsewhere in this patch.

It's possible that all CPUs of a certain type all offline, but I cannot
know the information here, because the boot CPU is the only online CPU.
I don't know the status of the other CPUs.

If we unconditionally register all PMUs, users may see a PMU in
/sys/devices, but they cannot use it, because there is no available CPU.
Is it acceptable that registering an empty PMU?


Thanks,
Kan

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