Bug 177561

Summary:	Largesmp kernel does not see all logical CPUs on IBM x460
Product:	Red Hat Enterprise Linux 4	Reporter:	Jim Paradis <jparadis>
Component:	kernel	Assignee:	Jim Paradis <jparadis>
Status:	CLOSED ERRATA	QA Contact:	Brian Brock <bbrock>
Severity:	medium	Docs Contact:
Priority:	medium
Version:	4.0	CC:	gbiswell, peterm
Target Milestone:	---
Target Release:	---
Hardware:	x86_64
OS:	Linux
Whiteboard:
Fixed In Version:	RHSA-2006-0132	Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2006-03-07 21:12:58 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:
Bug Blocks:	168430

Description Jim Paradis 2006-01-11 20:17:05 UTC

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.

Comment 3 Jim Paradis 2006-01-24 20:05:37 UTC

*** Bug 178839 has been marked as a duplicate of this bug. ***

Comment 5 Red Hat Bugzilla 2006-03-07 21:12:59 UTC

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