Added documentation about effects of CPU scaling events on daemon streams and patched daemon test scripts to disable CPU scaling

README.md

@@ -121,10 +121,11 @@ The following ARM platform have been used for testing:
 The BeagleBone® Black board with ARM Cortex-A8 32-Bit processor.
 See [Ubuntu 18.04 on BeagleBone® Black](https://elinux.org/BeagleBoardUbuntu) for additional information about how to setup Ubuntu on this board.
 
-The NanoPi NEO2 with Allwinner H5, Quad-core 64-bit high-performance Cortex A53 processor.
+The NanoPi NEO2 with Allwinner H5 Quad-core 64-bit Cortex A53 processor.
 See [Armbian NanoPi NEO2 ](https://www.armbian.com/nanopi-neo-2/) for additional information about how to setup Ubuntu on this board.
 
 The [ubuntu-packages.sh](ubuntu-packages.sh) script can be used to install all the packages required to compile and run the AES67 daemon, and the [platform compatibility test](#test).
+**_Important_** CPU scale events could affect daemon streams adding unexpected distortions, see [CPU scale events and scripts notes](#notes).
 **_Important_** _PulseAudio_ must be disabled or uninstalled for the daemon to work properly, see [PulseAudio and scripts notes](#notes).
 
 ## How to build ##
@@ -267,6 +268,22 @@ make sure that no instances of the aes67-daemon are running, enter the [tests](d
 
 * All the scripts in this repository are provided as a reference to help setting up the system and run the platform compatibility test.
   They have been tested on **Ubuntu 18.04 19.10 20.04** distros.
+* CPU scale events could have an impact on daemon streams causing unexpected distortion for a few seconds, see #96.
+Before running the daemon make sure you disable CPU scaling events:
+
+  Check if CPU scaling is enabled with:
+
+    cat /proc/sys/kernel/perf_cpu_time_max_percent
+
+  If result is not 0, (it's usually set to 25) set it to 0 with:
+
+    sudo sysctl -w kernel.perf_cpu_time_max_percent=0
+
+  You may also want to review the current CPU scaling governor with (cpu0 in this case):
+
+    cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
+
+  See https://www.kernel.org/doc/Documentation/cpu-freq/governors.txt for dditional info.
 * **PulseAudio** can create instability problems.
 Before running the daemon verify that PulseAudio is not running with:
 

daemon/scripts/disable_cpu_scaling.sh

@@ -0,0 +1,4 @@
+#!/bin/bash
+
+sudo sysctl -w kernel.perf_cpu_time_max_percent=0
+

run_latency_test.sh

@@ -107,6 +107,7 @@ trap cleanup EXIT
 
 #configure system parms
 sudo sysctl -w net/ipv4/igmp_max_memberships=66
+sudo sysctl -w kernel/perf_cpu_time_max_percent=0
 
 if [ -x /usr/bin/pulseaudio ]; then
   #stop pulseaudio, this seems to open/close ALSA continuosly

run_test.sh

@@ -94,6 +94,7 @@ trap cleanup EXIT
 
 #configure system parms
 sudo sysctl -w net/ipv4/igmp_max_memberships=66
+sudo sysctl -w kernel/perf_cpu_time_max_percent=0
 
 if [ -x /usr/bin/pulseaudio ]; then
   #stop pulseaudio, this seems to open/close ALSA continuosly