Chapter 35. Viewing preemption states

Processes using a CPU can give up the CPU they are using, either voluntarily or involuntarily.

35.1. Preemption

A process can voluntarily yield the CPU either because it has completed, or because it is waiting for an event, such as data from a disk, a key press, or for a network packet.

A process can also involuntarily yield the CPU. This is called preemption and occurs when a higher priority process wants to use the CPU.

Preemption can have a particularly negative impact on system performance, and constant preemption can lead to a state known as thrashing. This problem occurs when processes are constantly preempted, and no process ever runs to completion.

Changing the priority of a task can help reduce involuntary preemption.

35.2. Checking the preemption state of a process

You can check the voluntary and involuntary preemption status for a specified process. The statuses are stored in /proc/PID/status.


  • You have administrator privileges.


  • Display the contents of /proc/PID/status, where PID is the ID of the process. The following displays the preemption statuses for the process with PID 1000.

    # grep voluntary /proc/1000/status
    voluntary_ctxt_switches: 194529
    nonvoluntary_ctxt_switches: 195338