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--- embedded_systems:ethercat:test_and_tune_rt [2018-12-14 13:45] – angelegt mgehrig2
+++ embedded_systems:ethercat:test_and_tune_rt [2023-04-11 11:12] (aktuell) – Urs Graf
@@ Zeile 20: / Zeile 20: @@
 ''max. jitter OS = min jitter EtherCAT bus''
-See [[embedded_systems:ethercat:distributed_clocks|Distributed Clocks]] for more information.
+If the master cannot guarantee a stable clock, the masterShift mode is recommended.
+See [[embedded_systems:ethercat:understanding_ethercat:understanding_sync_with_dc|Distributed Clocks]] for more information.
+===== Measure RT Performance =====
+==== Cyclictest ====
+The Cyclictest is a software that can be used to easily measure the maximum jitter of a system.
+[[software:linux:realtime:cyclictest|Cyclictest]] explains how to install and use the software.
+=== Quick Measurement ===
+''sudo ./cyclictest -p 80 -t5 -n''
+===== Improve RT performance =====
+If the RT performance is not sufficient, the maximum jitter could be reduced with the following measures:
+==== Intel Scaling Governor ====
+Modern processors change the CPU frequency depending on the load to save power.
+With an RT-OS this can lead to increased jitter.
+If the frequency is fixed, the RT performance can be improved.
+ATTENTION: If the CPU is fixed at a high temperature, the CPU can run hot. If the Governor is changed manually, the CPU temperature should be monitored!
+The frequency is controlled by the OS by a [[https://wiki.archlinux.org/index.php/CPU_frequency_scaling#Scaling_governors|scaling governor]].
+The ''performance'' governor should run the cpu at the maximum frequency.
+To get the current active governor:\\
+''cpupower frequency-info''
+To set the governor:\\
+''sudo cpupower frequency-set -g powersave''
+==== Intel cstates ====
+Intel cstates indicate the power saving state of the processor.
+These states can be locked with kernel parameters on the C0 state (no power saving measures).
+{{:embedded_systems:ethercat:controlling_processor_c-state_usage_in_linux_v1.1_nov2013.pdf|Background information}}
+Display current kernel parameters:\\
+''cat /proc/cmdline''
+Add the following [[software:linux:linux_os:kernel_parameter|kernel parameters]]:
+  * cpuidle.off=1
+  * intel_idle.max_cstate=0

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