Raspberry Pi rt-kernel

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Compiler/tester un noyau temps-réel audio sur raspberry pi2

Test de latence du noyau

  • Setup : raspi2 + qjackctl 0.3.9 + sooperlooper 1.6.18 + carte son xenyx 302USB behringer

Outils de test

Connaitre les réglages actuel du noyau

zcat /proc/config.gz > ~/config

si il n'y à pas de fichier de configuration 

sudo modprobe configs

RealTimeConfigQuickScan

scripts qui permettent de connaitre la configuration du kernel 

git clone git://github.com/raboof/realtimeconfigquickscan.git
cd realtimeconfigquickscan
perl ./realTimeConfigQuickScan.pl

Cyclictest

Tester les performances temps réel 

git clone git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git 
cd rt-tests
make all
sudo cp ./cyclictest /usr/bin/
cd ~
sudo cyclictest -l1000000 -m -n -a0 -t1 -p99 -i400 -h400 -q

ou tester chaque coeurs 

sudo cyclictest -a -t -n -p99

Les résultats sont en microsecondes

  • source

https://www.osadl.org/Realtime-Preempt-Kernel.kernel-rt.0.html#externaltestingtool
https://github.com/raboof/realtimeconfigquickscan
http://www.linuxtopia.org/online_books/linux_kernel/kernel_configuration/ch08.html
https://rt.wiki.kernel.org/index.php/Cyclictest
http://people.redhat.com/williams/latency-howto/rt-latency-howto.txt

CCRMA Satellite pi2

https://ccrma.stanford.edu/~eberdahl/Satellite/

Installation/Configuration

CCRMA Satellite (une distribution créer pour faire de l'audio)

  • copier l'image su la carte sd
sudo dd if=/home/blablabla/SatelliteCCRMA_Rpi2_v1.03.dd of=/dev/mmcblk0 bs=4096
  • login et mot de passe
login : ccrma
mp : temppwd
  • arrêter les scripts par défaults
exit-stand-alone
sudo rm /etc/default/randomsound
sudo rm /etc/init.d/randomsound
sudo /home/ccrma/bin/disable-flash-writes
  • relancer le système
sudo reboot
  • lancer x
startx

Alors quoi?

  • test avec la carte son scarlett 2i2 : il faut modifier le fichier /boot/cmdline.txt et ajouter
dwc_otg.fiq_fsm_enable=0

source

  • test avec behringer xenyx302USB

pas de soucis de latence avec jack jusqu'à 48KHz, 128 échantillons : 5.33ms

Test de copie du kernel

Le coté audio de cette distribution étant plutôt satisfaisant, mais la surcouche concernant la protection en écriture et les scripts inutiles donnent envie de récupérer le kernel sur une distribution plus basique. 

Copie de /boot/kernel7.img 
Copie de /boot/bcm2709-rpi-2-b.dtb 
Copie de cmdline.txt
Copie de config.txt

sudo apt-get install cpufrequtils

modifier rc.local 

cpufreq-set -g performance
swapoff -a

sources:
https://www.bentasker.co.uk/documentation/linux/304-copying-a-linux-kernel-from-one-system-to-another
http://ubuntuforums.org/showthread.php?t=829472
https://forums.gentoo.org/viewtopic-t-813106-start-0.html
http://superuser.com/questions/439511/how-to-save-or-export-a-custom-linux-kernel-configuration
http://superuser.com/questions/287371/obtain-kernel-config-from-currently-running-linux-system

proc/version

ccrma@satellite ~/Desktop/realtime $ cat /proc/version 
Linux version 3.18.11-v7+ (dc4@dc4-XPS13-9333) (gcc version 4.8.3 20140303 (prerelease) (crosstool-NG linaro-1.13.1+bzr2650 - Linaro GCC 2014.03) ) #781 SMP PREEMPT Tue Apr 21 18:07:59 BST 2015


CyclicTest

Test avec SooperLooper 3 pistes, jack : 128 échantillons, 44100 Hz, 3 périodes/tampon 

ccrma@satellite ~ $ sudo cyclictest -a -t -n -p99
# /dev/cpu_dma_latency set to 0us
policy: fifo: loadavg: 0.78 0.45 0.24 4/220 4238          

T: 0 ( 4079) P:99 I:1000 C: 348228 Min:     10 Act:   26 Avg:   22 Max:     749
T: 1 ( 4080) P:99 I:1500 C: 232139 Min:      9 Act:   26 Avg:   19 Max:     205
T: 2 ( 4081) P:99 I:2000 C: 174114 Min:      9 Act:   38 Avg:   18 Max:     153
T: 3 ( 4082) P:99 I:2500 C: 139291 Min:      9 Act:   39 Avg:   20 Max:     717

QuickScan

ccrma@satellite ~/Desktop/realtime $ perl ./realTimeConfigQuickScan.pl 
== GUI-enabled checks ==
Checking if you are root... no - good
Checking filesystem 'noatime' parameter... 3.18.11 kernel - good
(relatime is default since 2.6.30)
Checking CPU Governors... CPU 0: 'performance' CPU 1: 'performance' CPU 2: 'performance' CPU 3: 'performance'  - good
Checking swappiness... 1 - good
Checking for resource-intensive background processes... none found - good
Checking checking sysctl inotify max_user_watches... < 524288 - not good
increase max_user_watches by adding 'fs.inotify.max_user_watches = 524288' to /etc/sysctl.conf and rebooting
For more information, see http://wiki.linuxaudio.org/wiki/system_configuration#sysctlconf
Checking access to the high precision event timer... not found - not good
/dev/hpet not found.
Checking access to the real-time clock... not found - not good
/dev/rtc not found (perhaps create a symlink?).
Checking whether you're in the 'audio' group... yes - good
Checking for multiple 'audio' groups... no - good
Checking the ability to prioritize processes with chrt... yes - good
Checking kernel support for high resolution timers... found - good
Kernel with Real-Time Preemption... not found - not good
Kernel without real-time capabilities found
For more information, see http://wiki.linuxaudio.org/wiki/system_configuration#installing_a_real-time_kernel
Checking if kernel system timer is set to 1000 hz... not found - not good
Try setting CONFIG_HZ to 1000 

Checking kernel support for tickless timer... found - good
== Other checks ==
Checking filesystem types... ok.
ok.
** Set $SOUND_CARD_IRQ to the IRQ of your soundcard to enable more checks.
   Find your sound card's IRQ by looking at '/proc/interrupts' and lspci.

Raspbian wheezy pi2

Version d'origine sans overclock 

pi@raspberrypi  cat /proc/version 
Linux version 3.18.11-v7+ (dc4@dc4-XPS13-9333) (gcc version 4.8.3 20140303 (prerelease) (crosstool-NG linaro-1.13.1+bzr2650 - Linaro GCC 2014.03) ) #781 SMP PREEMPT Tue Apr 21 18:07:59 BST 2015

CyclicTest

Test avec SooperLooper 3 pistes, jack : 128 échantillons, 44100 Hz, 3 périodes/tampon
SooperLooper : got Xrun après environ une minute de test 

pi@raspberrypi ~ $ sudo cyclictest -a -t -n -p99
# /dev/cpu_dma_latency set to 0us
policy: fifo: loadavg: 1.61 0.77 0.38 2/218 3923          

T: 0 ( 3910) P:99 I:1000 C:  94273 Min:     15 Act:   24 Avg:   45 Max:     867
T: 1 ( 3911) P:99 I:1500 C:  62852 Min:     17 Act:   26 Avg:   36 Max:     364
T: 2 ( 3912) P:99 I:2000 C:  47139 Min:     15 Act:   18 Avg:   31 Max:     421
T: 3 ( 3913) P:99 I:2500 C:  37711 Min:     15 Act:   29 Avg:   35 Max:     362

pi@raspberrypi ~ $ sudo cyclictest -l1000000 -m -n -a0 -t1 -p99 -i400 -h400 -q
# /dev/cpu_dma_latency set to 0us
# Histogram

# Total: 000249828
# Min Latencies: 00014
# Avg Latencies: 00036
# Max Latencies: 00730
# Histogram Overflows: 00088
# Histogram Overflow at cycle number:
# Thread 0: 09404 44073 44392 44551 44630 44869 44908 44988 44989 45025  225464 225760 226073 226682 227131 227653 228740 229146 229241 229244  229416 229797 229801 229893 229954 230007 230010 230071 230186 230275 230368 230467 230487 230545 230563 230680 230757 230916 231005 231099 231103 231195 231236 231332 231579 231713 232099 232959 233891 233892 234087 234464 234614 234621 236152 237379 237733 237818 237987 238038 238040 238078 238142 238236 238330 238474 238691 239425 239515 239608 239723 239726 240186 240189 240353 240467 241170 241259 241349 241539 241596 241630 241633 241724 241873 241907 241971 242005

QuickScan

pi@raspberrypi ~/realtimeconfigquickscan $ perl ./realTimeConfigQuickScan.pl
== GUI-enabled checks ==
Checking if you are root... no - good
Checking filesystem 'noatime' parameter... 3.18.11 kernel - good
(relatime is default since 2.6.30)
Checking CPU Governors... CPU 0: 'powersave' CPU 1: 'powersave' CPU 2: 'powersave' CPU 3: 'powersave'  - not good
Set CPU Governors to 'performance' with 'cpufreq-set -c <cpunr> -g performance'
See also: http://linuxmusicians.com/viewtopic.php?f=27&t=844
Checking swappiness... 1 - good
Checking for resource-intensive background processes... none found - good
Checking checking sysctl inotify max_user_watches... < 524288 - not good
increase max_user_watches by adding 'fs.inotify.max_user_watches = 524288' to /etc/sysctl.conf and rebooting
For more information, see http://wiki.linuxaudio.org/wiki/system_configuration#sysctlconf
Checking access to the high precision event timer... not found - not good
/dev/hpet not found.
Checking access to the real-time clock... not found - not good
/dev/rtc not found (perhaps create a symlink?).
Checking whether you're in the 'audio' group... yes - good
Checking for multiple 'audio' groups... no - good
Checking the ability to prioritize processes with chrt... yes - good
Checking kernel support for high resolution timers... found - good
Kernel with Real-Time Preemption... not found - not good
Kernel without real-time capabilities found
For more information, see http://wiki.linuxaudio.org/wiki/system_configuration#installing_a_real-time_kernel
Checking if kernel system timer is set to 1000 hz... not found - not good
Try setting CONFIG_HZ to 1000

Checking kernel support for tickless timer... found - good
== Other checks ==
Checking filesystem types... ok.
not found.
** Warning: no tmpfs partition mounted on /tmp
  For more information, see:
  - http://wiki.linuxaudio.org/wiki/system_configuration#tmpfs
  - http://lowlatency.linuxaudio.org
** Set $SOUND_CARD_IRQ to the IRQ of your soundcard to enable more checks.
  Find your sound card's IRQ by looking at '/proc/interrupts' and lspci.

RaspbianWheezy + modifs ccrma pi2

Comparaison wheezy/ccrma

Le /boot de la CCRMA-Satellite est identique à la Raspbian-Wheezy de base à part quelques modifications des fichiers cmdline.txt et config.txt et l'ajout de os_config.json.

  • /boot/cmdline.txt : En gras ce qui est ajouté sur la version CCRMA
dwc_otg.lpm_enable=0 console=ttyAMA0,115200 console=tty1 root=/dev/mmcblk0p6 rootfstype=ext4 elevator=deadline rootwait fastboot noswap cgroup_enable=memory

Pour comprendre les options de boot c'est par là

  • /etc/rc.local :il à aussi d'autres réglages dans le rc.local
sudo apt-get install cpufrequtils

modifier rc.local 

cpufreq-set -g performance
swapoff -a

QuickScan

pi@raspberrypi ~/realtimeconfigquickscan $ perl ./realTimeConfigQuickScan.pl
== GUI-enabled checks ==
Checking if you are root... no - good
Checking filesystem 'noatime' parameter... 3.18.11 kernel - good
(relatime is default since 2.6.30)
Checking CPU Governors... CPU 0: 'performance' CPU 1: 'performance' CPU 2:  'performance' CPU 3: 'performance'  - good
Checking swappiness... 1 - good
Checking for resource-intensive background processes... none found - good
Checking checking sysctl inotify max_user_watches... < 524288 - not good
increase max_user_watches by adding 'fs.inotify.max_user_watches = 524288' to /etc/sysctl.conf and rebooting
For more information, see http://wiki.linuxaudio.org/wiki/system_configuration#sysctlconf
Checking access to the high precision event timer... not found - not good
/dev/hpet not found.
Checking access to the real-time clock... not found - not good
/dev/rtc not found (perhaps create a symlink?).
Checking whether you're in the 'audio' group... yes - good
Checking for multiple 'audio' groups... no - good
Checking the ability to prioritize processes with chrt... yes - good
Checking kernel support for high resolution timers... found - good
Kernel with Real-Time Preemption... not found - not good
Kernel without real-time capabilities found
For more information, see  http://wiki.linuxaudio.org/wiki/system_configuration#installing_a_real-time_kernel
Checking if kernel system timer is set to 1000 hz... not found - not good
Try setting CONFIG_HZ to 1000

Checking kernel support for tickless timer... found - good
== Other checks ==
Checking filesystem types... ok.
not found.
** Warning: no tmpfs partition mounted on /tmp
   For more information, see:
  - http://wiki.linuxaudio.org/wiki/system_configuration#tmpfs
  - http://lowlatency.linuxaudio.org
** Set $SOUND_CARD_IRQ to the IRQ of your soundcard to enable more checks.
  Find your sound card's IRQ by looking at '/proc/interrupts' and lspci.

CyclicTest

pi@raspberrypi  $ sudo cyclictest -a -t -n -p99
# /dev/cpu_dma_latency set to 0us
policy: fifo: loadavg: 0.62 0.71 0.64 2/223 2689          

T: 0 ( 2686) P:99 I:1000 C:  30154 Min:     11 Act:   20 Avg:   33 Max:     396
T: 1 ( 2687) P:99 I:1500 C:  20103 Min:     11 Act:   26 Avg:   26 Max:     136
T: 2 ( 2688) P:99 I:2000 C:  15077 Min:     11 Act:   17 Avg:   28 Max:     136
T: 3 ( 2689) P:99 I:2500 C:  12061 Min:     12 Act:   19 Avg:   24 Max:      98

pi@raspberrypi  $ sudo cyclictest -l1000000 -m -n -a0 -t1 -p99 -i400 -h400 -q
# /dev/cpu_dma_latency set to 0us
# Histogram
# Total: 001000000
# Min Latencies: 00009
# Avg Latencies: 00022
# Max Latencies: 00311
# Histogram Overflows: 00000
# Histogram Overflow at cycle number:
# Thread 0:

Emlid-raspberryPi2-raspbian-rt

http://docs.emlid.com/navio/Downloads/Real-time-Linux-RPi2/

Pas moyen de lancer jack pour le moment, affaire à suivre...

Compilation du noyau depuis la pi

DOCUMENTATION EN COURS

Installation/Configuration

Test à partir d'une image minibian 2015-11-12-jessie-minibian

  • voir par ici pour les configurations de bases

Installer les dépendances

sudo apt-get install git bc libncurses5-dev gcc make screen ncurses-dev

Obtenir les sources

git clone --depth=1 https://github.com/raspberrypi/linux

Configuration du noyau

  • A partir du noyau actuel
zcat /proc/config.gz > ./.config
  • A partir de la configuration par défaut du raspberry

pour pi2 

KERNEL=kernel7 
make bcm2709_defconfig

pour les autres pi 

KERNEL=kernel
make bcmrpi_defconfig

Configurer les options du noyau

avec une interface pas très simple à naviguer 

make menuconfig

Kernel-config-cpu-scale.png

ou une interface plus feng shui 

make nconfig

puis sauvegarder les modifications comme .config


  • Sources :

https://www.raspberrypi.org/documentation/linux/kernel/building.md
https://github.com/raspberrypi/linux/tree/rpi-4.1.y

Compiler le nouveau noyau

  • Compilation (compter ~1h30 pour une pi2)
make -j4

(-j4) pour utiliser 4 processus en même temps ou bien pour créer un paquet (pas encore tester) 

make -j4 deb-pkg
  • Créer l'image du noyau et compiler les modules
make -j4 zImage modules dtbs
sudo make modules_install

Copier le nouveau noyau

sudo cp arch/arm/boot/dts/*.dtb /boot/
sudo cp arch/arm/boot/dts/overlays/*.dtb* /boot/overlays/
sudo cp arch/arm/boot/dts/overlays/README /boot/overlays/
sudo scripts/mkknlimg arch/arm/boot/zImage /boot/kernel-rt.img

Configurer le bootloader et tester le nouveau noyau

  • Éditer config.txt
sudo nano /boot/config.txt

et ajouter 

disable_splash=1
force_turbo=1
kernel=kernel-rt.img
  • Éditer cmdline.txt et ajouter en début de ligne
sudo nano /etc/cmdline.txt
sdhci_bcm2708.enable_llm=0 dwc_otg.speed=1
  • Redémarrer et test de version
sudo reboot
pi@minibian:~$ cat /proc/version 
Linux version 4.1.17-v7+ (pi@minibian) (gcc version 4.9.2 (Raspbian 4.9.2-10) ) #1 SMP Tue Feb 16 23:22:53 GMT 2016

En cas d'erreurs

  • Initialise la compilation mais garde le .config 
make clean
  • Initialise la compilation et supprime le .config
make mrproper

Patchage du noyau

Télécharger le patch temps réel

  • Il faut tout d'abord connaitre la version actuellement installer sur la pi
head Makefile -n 3

uname -r
  • Chercher par ici
  • puis télécharger le patch correspondant
wget https://www.kernel.org/pub/linux/kernel/projects/rt/4.1/older/patch-4.1.7-rt8.patch.gz
gunzip patch*


Appliquer le patch

cat patch-4.1.7-rt8.patch | patch -p1

sources

https://rt.wiki.kernel.org/index.php/RT_PREEMPT_HOWTO
http://framboisepi.fr/compilation-croise-du-kernel-linux-pour-raspberry-pi-2/
http://connect.ed-diamond.com/GNU-Linux-Magazine/GLMFHS-075/Raspberry-Pi-et-temps-reel
http://2014.capitoledulibre.org/symposion_media/media/coverage/linux-temps-reel-sur-raspberry-pi/Linux_RPi_TR_Capitole2014.pdf

sources

http://wiki.linuxaudio.org/wiki/system_configuration#build_your_own_real-time_kernel
https://www.raspberrypi.org/documentation/linux/kernel/building.md
http://www.talkunafraid.co.uk/2014/04/real-time-kernels-and-audio-on-the-raspberry-pi/
http://wiki.linuxaudio.org/wiki/system_configuration#quickscan
http://elinux.org/Raspberry_Pi_Kernel_Compilation
http://www.blaess.fr/christophe/2014/03/06/compilation-native-de-modules-kernel-sur-raspberry-pi/

Récupérée de « https://wiki.labomedia.org/index.php?title=Raspberry_Pi_rt-kernel&oldid=29736 »