PSI
also: Pressure Stall Information
PSI (Pressure Stall Information) is a Linux kernel metric that measures resource contention by tracking time processes spend waiting for CPU, memory, or I/O resources to become available.
PSI exposes kernel-level visibility into when applications are stalled due to resource scarcity, rather than actively running. It answers the question: "How much time is my workload blocked waiting for resources?"
PSI provides three main metrics: cpu.pressure (CPU scheduling delays), memory.pressure (memory reclaim stalls), and io.pressure (I/O wait time). Each metric shows the percentage of time processes spent stalled over 10-second, 60-second, and 300-second windows.
Example: A system under heavy memory pressure might show memory.pressure some avg10=25.5, indicating that on average, 25.5% of CPU cycles were spent with at least one process blocked waiting for memory. This helps distinguish between a genuinely slow system and one that's resource-constrained.
PSI is exposed through /proc/pressure/ and cgroup.pressure interfaces, making it invaluable for identifying performance bottlenecks and making scheduling decisions in container environments.