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SubjectRe: [PATCH V2 16/25] perf/x86: Register hybrid PMUs
On Thu, Mar 11, 2021 at 10:41:00AM -0500, Liang, Kan wrote:
>
>
> 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?

Sure. That's what it has a cpumask for after all.

ISTR that being the case with some dodgy RAPL thing on SPR as well.

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