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Reduce real-time priority to 98 #3

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Oct 31, 2022
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Reduce real-time priority to 98 #3

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6f2819f
reduce prior group by one
simutisernestas Oct 31, 2022
d9b6eeb
revert rtprio to 99 & leave comment in README
simutisernestas Oct 31, 2022
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reduce prior group by one
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@simutisernestas
simutisernestas committed Oct 31, 2022
commit 6f2819fda7ef51e63a847475725a13a0e4b09e81
6 changes: 2 additions & 4 deletions ReadMe.md
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Expand Up @@ -86,15 +86,13 @@ After having patched your system and restarted it, booting into the freshly inst
cap_add:
- SYS_NICE
ulimits:
rtprio: 99
rtprio: 98
rttime: -1 # corresponds to 'unlimited'
memlock: 8428281856
network_mode: host
```

Then **any process from inside the Docker can set real-time priorities `rtprio`** (e.g. by calling [`::pthread_setschedparam`](https://man7.org/linux/man-pages/man3/pthread_getschedparam.3.html) from inside the C/C++ code or by using [`chrt`](https://askubuntu.com/a/51285) from the command line).


Then **any process from inside the Docker can set real-time priorities `rtprio`** (e.g. by calling [`::pthread_setschedparam`](https://man7.org/linux/man-pages/man3/pthread_getschedparam.3.html) from inside the C/C++ code or by using [`chrt`](https://askubuntu.com/a/51285) from the command line). Note: [do NOT](https://github.com/ros2-realtime-demo/pendulum/blob/rolling/docs/real_time_linux.md#setting-permissions-for-the-scheduler) set rtprio to 99.

## 2. Example

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2 changes: 1 addition & 1 deletion doc/docker_realtime/ControlGroups.md
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Expand Up @@ -39,7 +39,7 @@ Similarly in a Docker-Compose file this can be achieved with (see the official D
privileged: true
cpu_rt_runtime: 950000
ulimits:
rtprio: 99
rtprio: 98
```

The real-time runtime `cpu.rt_runtime_us` allocated for each group can be inspected in `/sys/fs/cgroup/cpu,cpuacct`. In case you have already allocated a large portion of real-time runtime to another cgroup this might result in the error message `failed to write 95000 to cpu.rt_runtime_us: write /sys/fs/cgroup/cpu,cpuacct/system.slice/.../cpu.rt_runtime_us: invalid argument` or similar (as discussed [here](https://stackoverflow.com/questions/28493333/error-writing-to-cgroup-parameter-cpu-rt-runtime-us) and [here](https://github.com/moby/moby/issues/31411)). For more details on control groups in Linux see [here](https://www.kernel.org/doc/html/latest/scheduler/sched-rt-group.html) and [here](https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v1/cgroups.html). Now any process that is launched should be assigned to the corresponding real-time control group.
2 changes: 1 addition & 1 deletion docker/docker-compose.yml
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Expand Up @@ -9,7 +9,7 @@ services:
cap_add:
- SYS_NICE
ulimits:
rtprio: 99
rtprio: 98
rttime: -1
memlock: 8428281856
network_mode: host
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