dual xeons and linux kernel 2.6.16.13 - sees 4 processors instead of 2. Why?

Paul ptuohy at digibug.com
Fri May 5 00:21:17 CDT 2006


I have a Poweredge 1800 with dual Xeon processors. I just compiled the linux
2.6.16.13 kernel. In the kernel config, I set the Maximum number of CPUs
(NR_CPUS) to 2 because I have 2 processors. However, I notice that the boot
message reports the following:

ACPI: LAPIC (acpi_id[0x01] lapic_id[0x00] enabled)
Processor #0 15:4 APIC version 20
ACPI: LAPIC (acpi_id[0x02] lapic_id[0x06] enabled)
Processor #6 15:4 APIC version 20
ACPI: LAPIC (acpi_id[0x03] lapic_id[0x01] enabled)
Processor #1 15:4 APIC version 20
WARNING: NR_CPUS limit of 2 reached.  Processor ignored.
ACPI: LAPIC (acpi_id[0x04] lapic_id[0x07] enabled)
Processor #7 15:4 APIC version 20
WARNING: NR_CPUS limit of 2 reached.  Processor ignored.

If I switch my kernel config to 4 CPUs then all seems fine:

ACPI: LAPIC (acpi_id[0x01] lapic_id[0x00] enabled)
Processor #0 15:4 APIC version 20
ACPI: LAPIC (acpi_id[0x02] lapic_id[0x06] enabled)
Processor #6 15:4 APIC version 20
ACPI: LAPIC (acpi_id[0x03] lapic_id[0x01] enabled)
Processor #1 15:4 APIC version 20
ACPI: LAPIC (acpi_id[0x04] lapic_id[0x07] enabled)
Processor #7 15:4 APIC version 20


Is this because the Xeon processors are 64bit? Does the kernel see each
processor as 2 CPUs. Is there something wrong? Can anyone explain this to
me?

Thanks
PT






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