http://armadeus.org/wiki/index.php?action=history&feed=atom&title=Preempt-rtPreempt-rt - Revision history2026-04-04T06:33:10ZRevision history for this page on the wikiMediaWiki 1.26.3http://armadeus.org/wiki/index.php?title=Preempt-rt&diff=14386&oldid=prevJulienB: creation2017-07-12T17:07:14Z<p>creation</p>
<p><b>New page</b></p><div>preempt-rt are a series of patches to improve Linux kernel realtime performances. This page explain how to use it.<br />
<br />
==Installation==<br />
* Depending on your board, you may have a Buildroot defconfig to apply preempt-rt automatically. For example:<br />
<pre class=host><br />
$ make opos6ul-preempt-rt_defconfig<br />
</pre><br />
<br />
==Usage==<br />
* 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:<br />
<pre class=apf><br />
# chrt -p -f 20 X<br />
<br />
pid X's current scheduling policy: SCHED_OTHER<br />
pid X's current scheduling priority: 0<br />
pid X's new scheduling policy: SCHED_FIFO<br />
pid X's new scheduling priority: 20<br />
</pre><br />
* The more priority you set, the more your process is prioritary.<br />
* Priority queues are OTHER (no realtime), FIFO (First In First Out), RR (Round Robin time share)<br />
* 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:<br />
<pre class=apf><br />
# cyclictest -t 10 -p 20 -n -i 10000 --priospread<br />
<br />
/dev/cpu_dma_latency set to 0us<br />
policy: fifo: loadavg: 0.45 0.23 0.10 1/86 230 <br />
<br />
T: 0 ( 219) P:99 I:10000 C: 34012 Min: 67 Act: 166 Avg: 174 Max: 536<br />
T: 1 ( 220) P:98 I:10500 C: 32393 Min: 76 Act: 228 Avg: 202 Max: 719<br />
T: 2 ( 221) P:97 I:11000 C: 30920 Min: 66 Act: 170 Avg: 197 Max: 1154<br />
T: 3 ( 222) P:96 I:11500 C: 29576 Min: 65 Act: 217 Avg: 194 Max: 1176<br />
T: 4 ( 223) P:95 I:12000 C: 28343 Min: 72 Act: 167 Avg: 194 Max: 1912<br />
...<br />
</pre><br />
* times are in microseconds<br />
<br />
==Links==<br />
* https://wiki.linuxfoundation.org/realtime/documentation/howto/applications/preemptrt_setup<br />
* https://wiki.linuxfoundation.org/realtime/documentation/howto/applications/application_base<br />
<br />
[[Category:Real-Time]]</div>JulienB