Preempt-rt - Revision history

JulienB at 12:18, 27 May 2026

2026-05-27T12:18:02Z

← Older revision		Revision as of 13:18, 27 May 2026
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	preempt-rt are a series of patches to improve Linux kernel realtime performances. This page explain how to use it.		preempt-rt are a series of patches to improve Linux kernel realtime performances. This page explain how to use it.

			Since 6.12 version of Linux kernel, preempt-rt patches have been merged mainline and now just require a configuration option in Linux menuconfig to be activated (be sure to be in EXPERT mode first).

	==Installation==		==Installation==

JulienB at 16:53, 20 February 2025

2025-02-20T16:53:54Z

← Older revision		Revision as of 17:53, 20 February 2025
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	==Installation==		==Installation==
	* Depending on your board, you may have a Buildroot defconfig to apply preempt-rt ~~automatically~~. For example for [[OPOS6UL]]:		* Depending on your board, you may have a Buildroot defconfig to apply preempt-rt patches automagically. For example for [[OPOS6UL]]:
	<pre class=host>		<pre class=host>
	$ make opos6ul-preempt-rt_defconfig		$ make opos6ul-preempt-rt_defconfig

JulienB: /* Installation */

2025-02-20T16:26:18Z

Installation

← Older revision		Revision as of 17:26, 20 February 2025
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	==Installation==		==Installation==
	* Depending on your board, you may have a Buildroot defconfig to apply preempt-rt automatically. For example:		* Depending on your board, you may have a Buildroot defconfig to apply preempt-rt automatically. For example for [[OPOS6UL]]:
	<pre class=host>		<pre class=host>
	$ make opos6ul-preempt-rt_defconfig		$ make opos6ul-preempt-rt_defconfig
	</pre>		</pre>

			* If no config is available, you will have to do the job yourself, by finding a kernel version compatible with preempt-rt patches from https://www.kernel.org/pub/linux/kernel/projects/rt/

	==Usage==		==Usage==

JulienB: creation

2017-07-12T17:07:14Z

creation

New page

preempt-rt are a series of patches to improve Linux kernel realtime performances. This page explain how to use it.

==Installation==
* Depending on your board, you may have a Buildroot defconfig to apply preempt-rt automatically. For example:
<pre class=host>
$ make opos6ul-preempt-rt_defconfig
</pre>

==Usage==
* You can change realtime priority of tasks with ''chrt''. For example to set process X to priority 20 in FIFO scheduling queue, you have to do:
<pre class=apf>
# chrt -p -f 20 X

pid X's current scheduling policy: SCHED_OTHER
pid X's current scheduling priority: 0
pid X's new scheduling policy: SCHED_FIFO
pid X's new scheduling priority: 20
</pre>
* The more priority you set, the more your process is prioritary.
* Priority queues are OTHER (no realtime), FIFO (First In First Out), RR (Round Robin time share)
* You can validate realtime performances of your system with ''cyclictest''. For example to launch 10 processes triggering on timer set to 10ms with different descending priorities, you can do:
<pre class=apf>
# cyclictest -t 10 -p 20 -n -i 10000 --priospread

/dev/cpu_dma_latency set to 0us
policy: fifo: loadavg: 0.45 0.23 0.10 1/86 230

T: 0 ( 219) P:99 I:10000 C: 34012 Min: 67 Act: 166 Avg: 174 Max: 536
T: 1 ( 220) P:98 I:10500 C: 32393 Min: 76 Act: 228 Avg: 202 Max: 719
T: 2 ( 221) P:97 I:11000 C: 30920 Min: 66 Act: 170 Avg: 197 Max: 1154
T: 3 ( 222) P:96 I:11500 C: 29576 Min: 65 Act: 217 Avg: 194 Max: 1176
T: 4 ( 223) P:95 I:12000 C: 28343 Min: 72 Act: 167 Avg: 194 Max: 1912
...
</pre>
* times are in microseconds

==Links==
* https://wiki.linuxfoundation.org/realtime/documentation/howto/applications/preemptrt_setup
* https://wiki.linuxfoundation.org/realtime/documentation/howto/applications/application_base

[[Category:Real-Time]]