taskset

taskset [options] mask command [arg]...
taskset [options] -p [mask] pid

taskset is used to set or retrieve the CPU affinity of a running process given its PID or to launch a new COMMAND with a given CPU affinity. CPU affinity is a scheduler property that "bonds" a process to a given set of CPUs on the system. The Linux scheduler will honor the given CPU affinity and the process will not run on any other CPUs. Note that the Linux scheduler also supports natural CPU affinity: the scheduler attempts to keep processes on the same CPU as long as practical for performance reasons. Therefore, forcing a specific CPU affinity is useful only in certain applications.

The CPU affinity is represented as a bitmask, with the lowest order bit corresponding to the first logical CPU and the highest order bit corresponding to the last logical CPU. Not all CPUs may exist on a given system but a mask may specify more CPUs than are present. A retrieved mask will reflect only the bits that correspond to CPUs physically on the system. If an invalid mask is given (i.e., one that corresponds to no valid CPUs on the current system) an error is returned. The masks are typically given in hexadecimal. For example,

0x00000001

is processor #0

0x00000003

is processors #0 and #1

0xFFFFFFFF

is all processors (#0 through #31).

When taskset returns, it is guaranteed that the given program has been scheduled to a legal CPU.

-a, --all-tasks

Set or retrieve the CPU affinity of all the tasks (threads) for a given PID.

-p, --pid

Operate on an existing PID and do not launch a new task.

-c, --cpu-list

Specify a numerical list of processors instead of a bitmask. The numbers are separated by commas and may include ranges. For example: 0,5,7,9-11.

-h, --help

Display usage information and exit.

-V, --version

Display version information and exit.

The default behavior is to run a new command with a given affinity mask:

taskset mask command [arguments]

You can also retrieve the CPU affinity of an existing task:

taskset -p pid

Or set it:

taskset -p mask pid

A user must possess CAP_SYS_NICE to change the CPU affinity of a process. Any user can retrieve the affinity mask.

Written by Robert M. Love.

Copyright © 2004 Robert M. Love
This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

chrt(1), nice(1), renice(1), sched_setaffinity(2), sched_getaffinity(2)

See sched_setscheduler(2) for a description of the Linux scheduling scheme.

The taskset command is part of the util-linux package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.