UCLAMPSET(1) User Commands UCLAMPSET(1)
NAME
uclampset - manipulate the utilization clamping attributes of the
system or a process
SYNOPSIS
uclampset [options] [-m uclamp_min] [-M uclamp_max] _command argument
uclampset [options] [-m uclamp_min] [-M uclamp_max] -p PID
DESCRIPTION
uclampset sets or retrieves the utilization clamping attributes of an
existing PID, or runs command with the given attributes.
Utilization clamping is a new feature added in v5.3. It gives a hint to
the scheduler about the allowed range of utilization the task should be
operating at.
The utilization of the task affects frequency selection and task
placement. Only schedutil cpufreq governor understands handling util
clamp hints at the time of writing. Consult your kernel docs for
further info about other cpufreq governors support.
If you’re running on asymmetric heterogeneous system like Arm’s
big.LITTLE. Utilization clamping can help bias task placement. If the
task is boosted such that util_min value is higher than the little
cores' capacity, then the scheduler will do its best to place it on a
big core.
Similarly, if util_max is smaller than or equal the capacity of the
little cores, then the scheduler can still choose to place it there
even if the actual utilization of the task is at max.
Setting a task’s uclamp_min to a none zero value will effectively boost
the task as when it runs it’ll always start from this utilization
value.
By setting a task’s uclamp_max below 1024, this will effectively cap
the task as when it runs it’ll never be able to go above this
utilization value.
The full utilization range is: [0:1024]. The special value -1 is used
to reset to system’s default.
OPTIONS
-m
Set util_min value.
-M
Set util_max value.
-a, --all-tasks
Set or retrieve the utilization clamping attributes of all the
tasks (threads) for a given PID.
-p, --pid
Operate on an existing PID and do not launch a new task.
-s, --system
Set or retrieve the system-wide utilization clamping attributes.
-R, --reset-on-fork
Set SCHED_FLAG_RESET_ON_FORK flag.
-v, --verbose
Show status information.
-h, --help
Display help text and exit.
-V, --version
Print version and exit.
USAGE
The default behavior is to run a new command:
uclampset [-m uclamp_min] [-M uclamp_max] command [arguments]
You can also retrieve the utilization clamping attributes of an
existing task:
uclampset -p PID
Or set them:
uclampset -p PID [-m uclamp_min] [-M uclamp_max]
Or control the system-wide attributes:
uclampset -s [-m uclamp_min] [-M uclamp_max]
PERMISSIONS
A user must possess CAP_SYS_NICE to change the scheduling attributes of
a process. Any user can retrieve the scheduling information.
NOTES
The system wide utilization clamp attributes are there to control the
allowed range the tasks can use. By default both uclamp_min and
uclamp_max are set to 1024. This means users can set the utilization
clamp values for their task across the full range [0:1024].
For example:
uclampset -s -m 512 -M 700
will prevent any task from being boosted higher than 512. And all tasks
in the systems are capped to a utilization of 700. Effectively
rendering the maximum performance of the system to 700.
Consult your kernel docs for the exact expected behavior on that
kernel.
AUTHORS
Qais Yousef <qais.yousef@arm.com>
SEE ALSO
nice(1), renice(1), taskset(1), sched(7)
See sched_setscheduler(2) and sched_setattr(2) for a description of the
Linux scheduling scheme.
REPORTING BUGS
For bug reports, use the issue tracker at
https://github.com/util-linux/util-linux/issues.
AVAILABILITY
The uclampset command is part of the util-linux package which can be
downloaded from Linux Kernel Archive
<https://www.kernel.org/pub/linux/utils/util-linux/>.
util-linux 2.38.1 2022-05-11 UCLAMPSET(1)
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