IBM AIX 7.3 – Common Problem 239 – Diagnosis and Fix

📖 ~1 min read

Table of contents

1. Symptom & Impact
2. Environment & Reproduction
3. Root Cause Analysis
4. Quick Triage
5. Step-by-Step Diagnosis
6. Solution – Primary Fix
7. Solution – Alternative Approaches
8. Verification & Acceptance Criteria
9. Rollback Plan
10. Prevention & Hardening
11. Related Errors & Cross-Refs
12. References & Further Reading

Symptom & Impact

lparstat shows low %busy but applications report CPU contention and high response times.

Environment & Reproduction

Common on shared-processor LPARs with smt and processor folding enabled under low load.

Root Cause Analysis

AIX folds idle virtual processors; bursty workloads pay a wake-up penalty.

Quick Triage

Run lparstat 2 5, mpstat -s, and topas to view folded LCPUs and run queue.

Step-by-Step Diagnosis

Inspect schedo -L vpm_xvcpus and vpm_fold_policy attributes.

Solution – Primary Fix

Tune folding with schedo -p -o vpm_xvcpus=N or disable for latency-sensitive workloads.

Solution – Alternative Approaches

Increase entitled capacity or set the LPAR to dedicated mode if folding cannot be tuned away.

Verification & Acceptance Criteria

lparstat shows app%busy steady and response times return to SLA.

Rollback Plan

Revert schedo changes with schedo -d vpm_xvcpus and re-evaluate workload profile.

Prevention & Hardening

Baseline vpm settings per workload class and track via nmon collectors.

Related Errors & Cross-Refs

Often paired with high runq in topas and ksh latency complaints.

Related tutorial: View the step-by-step tutorial for aix-7.3.

View all aix-7.3 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

IBM AIX 7.3 lparstat and schedo reference – processor folding section.