ITT - Integrated Task Time

Enhanced Definition

`Integrated Task Time (ITT)` is a cumulative measure of the total processor time consumed by a task or address space in the z/OS environment. It includes both `Task Control Block (TCB)` time and `Service Request Block (SRB)` time, providing a comprehensive view of the CPU resources directly attributable to a specific workload. ITT is a fundamental metric for performance analysis, accounting, and chargeback in mainframe systems.

Key Characteristics

- Comprehensive CPU Metric: ITT aggregates TCB time (CPU time spent executing user code and system services on behalf of the task) and SRB time (CPU time spent by system routines performing services for the task, often asynchronously).
- Accounting and Billing Basis: It is a primary metric used by z/OS for workload accounting, chargeback, and billing purposes, as it represents the direct CPU consumption of a job or started task.
- Granularity: ITT is typically measured in microseconds or milliseconds and is recorded by the system for each task, step within a job, or for an entire address space.
- Excludes I/O Wait Time: ITT specifically measures CPU execution time and does not include time spent waiting for I/O operations to complete, making it a pure measure of processor utilization.
- Recorded in SMF: ITT values are meticulously recorded in System Management Facilities (SMF) records (e.g., Type 30 records for jobs/steps, Type 72 for WLM reporting), making it available for post-processing and analysis.
- Reflects Workload Demand: High ITT values indicate significant CPU demand from a particular workload, which is crucial for performance tuning and capacity planning.

Use Cases

- Workload Performance Analysis: Analyzing ITT for specific jobs, started tasks, or applications helps identify CPU-intensive workloads that might be candidates for optimization or require additional processing capacity.
- Chargeback and Billing: Many mainframe installations use ITT as a primary metric to charge internal departments or external clients for their CPU resource consumption.
- Capacity Planning: Tracking ITT trends over time for critical applications assists in forecasting future CPU requirements and planning for hardware upgrades or workload rebalancing.
- Problem Determination: A sudden or unexpected increase in ITT for a stable application can signal a performance regression, an inefficient code change, or an unexpected workload spike, prompting investigation.
- Workload Manager (WLM) Goal Setting: While WLM primarily manages based on service units, understanding the ITT consumption of a workload helps in defining appropriate WLM service classes and performance goals.

Related Concepts

ITT is a critical component of overall CPU utilization on z/OS, directly combining TCB time and SRB time, which are the two primary categories of CPU consumption for a task. It is distinct from elapsed time, as ITT only measures active CPU work, excluding I/O wait time. ITT values are captured in SMF records, which are then processed by tools like RMF (Resource Measurement Facility) or third-party performance monitors to provide insights into system and workload performance. WLM uses ITT (converted to service units) as part of its resource management decisions, aiming to