Messages in this thread | | | Subject | Re: Question about prefill_possible_map | From | Cao jin <> | Date | Wed, 8 Apr 2020 20:07:16 +0800 |
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Hi Thomas,
Seems you helped improve 2a51fe083eba7f, could you help with this question?
-- Sincerely, Cao jin
On 3/27/20 2:38 PM, Cao jin wrote: > Hi, > > At the beginning of this function, there is: > > /* No boot processor was found in mptable or ACPI MADT */ > if (!num_processors) { > if (boot_cpu_has(X86_FEATURE_APIC)) { > int apicid = boot_cpu_physical_apicid; > int cpu = hard_smp_processor_id(); > > pr_warn("Boot CPU (id %d) not listed by BIOS\n", cpu); > > /* Make sure boot cpu is enumerated */ > if (apic->cpu_present_to_apicid(0) == BAD_APICID && > apic->apic_id_valid(apicid)) > generic_processor_info(apicid, boot_cpu_apic_version); > } > > if (!num_processors) > num_processors = 1; > } > > I see 3 cases will go through this code chunk, > > 1. UP, has no APCI MADT & MP table, but has APIC > 2. 2a51fe083eba7f: kdump kernel running on the hot-plugged CPU > 3. normal UP(No table, no APIC) > > And "if (boot_cpu_has(X86_FEATURE_APIC))" covers case 1 & 2 to my > understanding. > > But both cases 1 & 2 already have boot_cpu_physical_apicid initialized > from APIC ID register: > 1. init_apic_mappings --> register_lapic_address > 2. early_acpi_boot_init --> early_acpi_process_madt -->...--> > register_lapic_address > > So my question is: is variable "cpu" redundant? Could it be: > > diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c > index 69881b2d446c..99fc03511568 100644 > --- a/arch/x86/kernel/smpboot.c > +++ b/arch/x86/kernel/smpboot.c > @@ -1456,9 +1456,9 @@ __init void prefill_possible_map(void) > if (!num_processors) { > if (boot_cpu_has(X86_FEATURE_APIC)) { > int apicid = boot_cpu_physical_apicid; > - int cpu = hard_smp_processor_id(); > > - pr_warn("Boot CPU (id %d) not listed by BIOS\n", cpu); > + pr_warn("Boot CPU (id %d) not listed by BIOS\n", \ > + boot_cpu_physical_apicid); > > /* Make sure boot cpu is enumerated */ > if (apic->cpu_present_to_apicid(0) == BAD_APICID && >
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