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minimal_memory_lock package from ros2-realtime-examples repo

minimal_cpu_affinity minimal_memory_lock minimal_scheduling

ROS Distro
github

Package Summary

Tags	No category tags.
Version	0.0.1
License	Apache License 2.0
Build type	AMENT_CMAKE
Use	RECOMMENDED

Repository Summary

Description	Minimal ROS 2 real-time cookbook recipes
Checkout URI	https://github.com/ros-realtime/ros2-realtime-examples.git
VCS Type	git
VCS Version	rolling
Last Updated	2023-06-05
Dev Status	UNKNOWN
Released	UNRELEASED
Tags	real-time cpp realtime ros ros2 rclcpp
Contributing	Help Wanted (-) Good First Issues (-) Pull Requests to Review (-)

Package Description

Examples of minimal memory lock configuration

Additional Links

No additional links.

Maintainers

Carlos San Vicente

Authors

Carlos San Vicente

minimal_memory_lock/README.md

minimal_memory_lock

Description

Page faults is a non-deterministic event and should be avoided during real-time execution.

This example shows how to lock the process virtual memory into physical RAM in order to prevent page faults happening during the applications real-time runtime phase.

Requirements

Adjust permissions for memory locking. Add to /etc/security/limits.conf (as sudo):

<your username>    -   memlock   <limit in kB>

Adding some memory stress

While running the examples, you can use stress-ng to generate stress the memory and generate page faults. Run the following command in another terminal before running the example:

$ stress-ng --fault 0 --perf -t 1m
# for newer kernels
$ stress-ng --userfaultfd 0 --perf -t 1m

How to run

No memory lock

By default, the memory is not locked, and we can see some page faults while the node is spinning.

$ ros2 run minimal_memory_lock minimal_memory_lock
Process memory before node creation:  13 MB
Process memory is not being locked. Memory page faults may occur.
Process memory before spin:  13 MB
Total page faults before spin [Minor: 789, Major: 0]
[WARN] [1651228546.831772017] [minimal_publisher]: New page faults during spin: [minor: 3, major: 0]
[WARN] [1651228547.331783493] [minimal_publisher]: New page faults during spin: [minor: 3, major: 0]
[INFO] [1651228547.831905095] [minimal_publisher]: New page faults during spin: [minor: 0, major: 0]
[INFO] [1651228548.331781121] [minimal_publisher]: New page faults during spin: [minor: 0, major: 0]
[INFO] [1651228548.831736137] [minimal_publisher]: New page faults during spin: [minor: 0, major: 0]
[INFO] [1651228549.331774937] [minimal_publisher]: New page faults during spin: [minor: 0, major: 0]
[INFO] [1651228549.831664055] [minimal_publisher]: New page faults during spin: [minor: 0, major: 0]
[INFO] [1651228550.331663058] [minimal_publisher]: New page faults during spin: [minor: 0, major: 0]
[INFO] [1651228550.831664222] [minimal_publisher]: New page faults during spin: [minor: 0, major: 0]
[INFO] [1651228551.331658742] [minimal_publisher]: New page faults during spin: [minor: 0, major: 0]
[INFO] [1651228551.831660235] [minimal_publisher]: New page faults during spin: [minor: 0, major: 0]
[INFO] [1651228552.331768024] [minimal_publisher]: New page faults during spin: [minor: 0, major: 0]
[WARN] [1651228552.831653605] [minimal_publisher]: New page faults during spin: [minor: 1, major: 0]
[INFO] [1651228553.331652699] [minimal_publisher]: New page faults during spin: [minor: 0, major: 0]
[INFO] [1651228553.831650582] [minimal_publisher]: New page faults during spin: [minor: 0, major: 0]
[WARN] [1651228554.331644228] [minimal_publisher]: New page faults during spin: [minor: 1, major: 0]

Using the --allocate-in-node we can simulate the node allocating some memory on the heap when spinning.

If we allocate 50 MBytes each time we can see page faults generated more frequently:

$ ros2 run minimal_memory_lock minimal_memory_lock --allocate-in-node 50
Process memory before node creation:  13 MB
Process memory is not being locked. Memory page faults may occur.
Process memory before spin:  13 MB
Total page faults before spin [Minor: 790, Major: 0]
[WARN] [1651228794.768297975] [minimal_publisher]: New page faults during spin: [minor: 12800, major: 0]
[WARN] [1651228795.268509771] [minimal_publisher]: New page faults during spin: [minor: 12803, major: 0]
[WARN] [1651228795.767921477] [minimal_publisher]: New page faults during spin: [minor: 12800, major: 0]
[WARN] [1651228796.267221048] [minimal_publisher]: New page faults during spin: [minor: 12800, major: 0]
[WARN] [1651228796.769758758] [minimal_publisher]: New page faults during spin: [minor: 12800, major: 0]
[WARN] [1651228797.271399242] [minimal_publisher]: New page faults during spin: [minor: 12800, major: 0]
[WARN] [1651228797.773109372] [minimal_publisher]: New page faults during spin: [minor: 12800, major: 0]

Locking the memory

Using the --lock-memory option we enforce all the process virtual memory to be locked into the physical RAM memory. Now we expect to see no page faults in the spin phase.

```bash $ ros2 run minimal_memory_lock minimal_memory_lock –lock-memory Process memory before node creation: 13 MB Process memory before locking: 13 MB

File truncated at 100 lines see the full file

CHANGELOG

No CHANGELOG found.

Package Dependencies

Deps	Name
	rclcpp
	std_msgs
	ament_cmake
	ament_lint_auto
	ament_lint_common

System Dependencies

No direct system dependencies.

Dependant Packages

No known dependants.

Launch files

No launch files found

Messages

No message files found.

Services

No service files found

Plugins

No plugins found.

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