Some records during the development of ros2/ros1

Actually , It's going on ROS2/ROS1 When programming , You usually need to start many nodes , Sometimes greater than 60+ Nodes are also very common .

that , You need to schedule these nodes . Different nodes work at different frequencies , Some are 10Hz Can , Some need 1000Hz.

Basic concepts ：

• taskset
• isolcpus

taskset Used in a given pid Set or retrieve the of the running process CPU Affinity , Or start with a given CPU The new command of affinity . CPU Affinity is a scheduler property , It will make the process “ binding ” To a set of given on the system CPU. Linux The scheduler will follow the given CPU Affinity , And the process will not be in any other CPU Up operation . Please note that ,Linux The scheduler also supports natural CPU Affinity ： For performance reasons , The scheduler will try to keep the process in the same CPU On , As long as it works . therefore , Force specific CPU Affinity is only useful in some applications .

CPU Affinity is expressed as a bit mask , The lowest bit corresponds to the first logic CPU, The highest bit corresponds to the last logic CPU. Not all CPU Can exist on a given system , But the mask may specify more than existing CPU. The retrieved mask will only reflect the physical CPU The corresponding bit . If an invalid mask is given （ namely , It corresponds to that there is no valid CPU The mask of ）, It will return an error . Masks are usually given in hexadecimal . for example ,

•            0x00000001 It's the processor #0
•            0x00000003 It's the processor #0 and #1
•            0xFFFFFFFF Yes, all processors （#0 To #31）

When the task set returns , It can ensure that the given program has been dispatched to a legal CPU On .

isolcpus We need to pay attention to amd and intel The difference , If it is arm or nVidia……

In extreme cases, the performance is unstable , perhaps CPU completely fill .

use  "events executor", This is in ROS 2 Humble You can use it directly , Other previous versions need to compile the corresponding source code .

Callback function or time

FastDDS It needs to be configured before using , This is better .

otherwise , Sometimes FastDDS Cannot list nodes after restarting nodes while other nodes are running / The theme .

Specific to see discovery_server; Or switch to CycloneDDS 

If you choose CycloneDDS, Configuration is also required , Instead of using default parameters directly .

ROS_DOMAIN_ID The same configuration will make the network overburdened in the case of a large number of network needs or multiple robots ……

colcon build It's best to add some parameters, otherwise it's not easy to use .

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