pressure stall information
also: PSI
Pressure Stall Information (PSI) is a kernel mechanism that measures how long processes are delayed waiting for system resources like CPU, memory, or I/O, providing visibility into resource contention.
Pressure Stall Information (PSI) quantifies the percentage of time that tasks on a system are blocked or delayed due to insufficient resources. Rather than just measuring resource utilization, PSI tracks actual stalls experienced by applications—how long they wait for CPU time, memory allocation, or disk I/O.
PSI data is exposed through /proc/pressure/ with three files: cpu, memory, and io. Each shows metrics like some (some tasks stalled) and full (all tasks stalled) over 10-second, 60-second, and 300-second windows.
For example, high CPU PSI indicates processes are frequently waiting for CPU scheduling, while high memory PSI suggests the system is under memory pressure. This helps identify true bottlenecks: a system might show 50% CPU utilization but have 0% CPU PSI (no stalls), meaning workloads are genuinely getting resources.