When booting largesmp kernel on a 4-node IBM x460, only 32 logical CPUs are reported. Since the 4-node configuration has 16 dual-core hyperthreaded CPUs, there should be 64 logical CPUs present. The system console log shows entries like this: ACPI: LAPIC (acpi_id[0x20] lapic_id[0x80] enabled) Processor #128 invalid (max 128) ACPI: LAPIC (acpi_id[0x21] lapic_id[0x81] enabled) Processor #129 invalid (max 128) ACPI: LAPIC (acpi_id[0x22] lapic_id[0x82] enabled) Processor #130 invalid (max 128) ACPI: LAPIC (acpi_id[0x23] lapic_id[0x83] enabled) Processor #131 invalid (max 128) ACPI: LAPIC (acpi_id[0x24] lapic_id[0xa6] enabled) Processor #166 invalid (max 128) ACPI: LAPIC (acpi_id[0x25] lapic_id[0xa7] enabled) Processor #167 invalid (max 128) ACPI: LAPIC (acpi_id[0x26] lapic_id[0xa4] enabled) Processor #164 invalid (max 128) ACPI: LAPIC (acpi_id[0x27] lapic_id[0xa5] enabled) Processor #165 invalid (max 128) The reason for this is that the local-APIC assignment for CPUs on this box is sparse; there are gaps in the APIC sequence from one node to the next. This means that although there are "only" 64 logical CPUs, the APIC IDs could be anything in the theoretical range 0-254. On stock RHEL4, for whatever reason, MAX_APICS is set to 128. Bumping MAX_APICS to 255 fixes this problem, and this patch has been submitted for review to include in a RHEL4 update.
*** Bug 178839 has been marked as a duplicate of this bug. ***
An advisory has been issued which should help the problem described in this bug report. This report is therefore being closed with a resolution of ERRATA. For more information on the solution and/or where to find the updated files, please follow the link below. You may reopen this bug report if the solution does not work for you. http://rhn.redhat.com/errata/RHSA-2006-0132.html