Install and Configure JACK
This has been copied from 2.3 of the Fedora Musicians guide
- Use PackageKit or Apper to install the jack-audio-connection-kit and qjackctl packages.
- Review and approve the installation, making sure that it completes correctly.
- Run QjackCtl from the KMenu or the Applications menu.
- To start the JACK server click Start. To stop the JACK server click Stop.
- Click Messages to see messages, which are usually errors or warnings.
- Click Status to see various statistics about the currently-running server.
- Click Connections button to see and adjust the connections between applications and audio hardware.
By default, QjackCtl configures JACK to use the 'default' sound card. The 'default' sound card uses all features of the ALSA driver even though JACK provides the same features. To save memory and processor time, you should configure QjackCtl with a specific sound card.
- Open a terminal. In GNOME, choose Applications → System → Terminal. In KDE, click on the application launcher, then choose System → Konsole.
- Execute this command: cat /proc/asound/cards
- The cat program outputs a list of sound cards in your computer that looks similarly to the output below.
0 [SB ]: HDA-Intel - HDA ATI SB HDA ATI SB at 0xf7ff4000 irq 16 1 [MobilePre ]: USB-Audio - MobilePre M Audio MobilePre at usb-0000:00:13.0-2In this example output, the square brackets surround the name of the sound card. The names of the sound cards in this example output are SB and MobilePre.Identify the name of the sound card that you want to use. If you do not see your sound card in the list outputted by cat, then your computer does not detect it.
- Start QjackCtl.
- Click Setup to open the "Setup" window.
- In the 'Interface' text box, type the name of your preferred sound card with "hw:" in front. With the sound cards listed above, you might write hw:MobilePre.
- Save your settings by exiting QjackCtl. If you want to use JACK, restart QjackCtl.
Using the Jack D-Bus Interface
Control applications such as qjackctl can be configured to interact with the jack sound server using D-Bus. This has the advantage of allowing jack to request the release of the sound device from Pulseaudio (see below).
jackdbus is shipped in a separate package. To install this (as root) do:
yum install jack-audio-connection-kit-dus
Finally, check "Enable D-Bus interface" in Setup -> Misc within Qjackctl
Integrate Jack with Pulseaudio
Jack will ask Pulse Audio through D-Bus for ownership of the sound card. Pulse Audio will grant it and Jack will have complete control of it. No conflicts and no configuration necessary. In this case Pulse Audio will stop using the card and if it is the only one, you will not have sound for system sounds, browser media playback, etc (which is usually what you want). Otherwise it is possible to load a Pulse Audio module that redirects PA to use Jack.
Running Jack in Realtime mode
The JACK server jackd has the capability to run in a real-time mode which greatly decreases the chance of audio glitches. The real-time mode is enabled by passing the -R or --realtime option to jackd when starting the server. It is only possible to run jackd in real-time mode as a non-root user by modifying your PAM configuration, PAM stands for Pluggable Authentication Modules and is the primary authentification mechanism used on Fedora. The primary source of PAM documentation can be found at the following at http://www.kernel.org/pub/linux/libs/pam/
The specific PAM configuration file that needs to be modified is /etc/security/limits.conf and it controls the system resource limits. It is important to understand that modifying the resource limits configuration files can decrease the security of your system. Documentation specific to the resource limits PAM module can be found at http://www.kernel.org/pub/linux/libs/pam/Linux-PAM-html/pam-6.html#ss6.12
Alternatively, one can create a new file
/etc/security/limits.d/<priority>-<name>.conf
that contains the resource limits for individual users and/or groups. The jack-audio-connection-kit package that comes with Fedora contains the file
/etc/security/limits.d/99-jack.conf
that does this job for you.
The resource limits that need to be changed to allow jackd to run in realtime mode are named rtprio and memlock. To increase the limits for a specific user named fred you would add the following to /etc/security/limits.conf
fred - rtprio 70 fred - memlock 50000
The value of rtprio can be set in the range 0 - 99 where any value greater that 0 will allow the user to change the scheduling policy to "real-time". By default the JACK server requires a minimum rtprio setting of 20 but jackd will accept a command line parameter -P or --realtime-priority which will change the minimum required value of rtprio that is needed, but the default of 20 is nearly always sufficient.
The appropriate value for memlock is dependent on the amount of memory present in the system but a minimum value of 50000(50MB) and a maximum value of half the available memory can be used as a rough guideline.
To verify that the resource limits have been modified you can use the bash built-in ulimit command, for example:
$ulimit -a core file size (blocks, -c) 0 data seg size (kbytes, -d) unlimited max nice (-e) 0 file size (blocks, -f) unlimited pending signals (-i) 8191 max locked memory (kbytes, -l) 50000 max memory size (kbytes, -m) unlimited open files (-n) 1024 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 max rt priority (-r) 70 stack size (kbytes, -s) 10240 cpu time (seconds, -t) unlimited max user processes (-u) 8191 virtual memory (kbytes, -v) unlimited file locks (-x) unlimited file locks (-x) unlimited
Keep in mind that you may have to re-login before changes to limits.conf, or additions to the limits.d/ directory to take effect.
rtirq
rtirq is a startup script which allows you to tune the realtime priority of software IRQ threads handling audio devices.
As root:
yum install rtirq
For rtirq to function you will need to append the threadirqs parameter to the kernel command line.
To set this as default for newly installed kernels add it to the GRUB_CMDLINE_LINUX variable in /etc/default/grub (grub2).
The default realtime priorities chosen in the rtirq package are those that work best with Jack defaults. You can tailor rtirq to your specific hardware needs by editing /etc/sysconfig/rtirq
To list available IRQ's:
cat /proc/interrupts
CPU0 CPU1 CPU2 CPU3
0: 137 0 0 0 IO-APIC-edge timer
1: 88 0 0 0 IO-APIC-edge i8042
8: 1 0 0 0 IO-APIC-edge rtc0
9: 1064 0 0 0 IO-APIC-fasteoi acpi
12: 195 0 0 0 IO-APIC-edge i8042
16: 269 63 0 0 IO-APIC-fasteoi ehci_hcd:usb1
17: 0 0 0 0 IO-APIC-fasteoi ath9k
19: 0 0 0 0 IO-APIC-fasteoi xhci_hcd:usb3
23: 39 0 0 0 IO-APIC-fasteoi ehci_hcd:usb2
41: 8357 18983 9722 12125 PCI-MSI-edge ahci
42: 42399 0 0 0 PCI-MSI-edge i915
43: 26616 0 0 0 PCI-MSI-edge p5p1
44: 12 0 0 0 PCI-MSI-edge mei
45: 672 0 0 0 PCI-MSI-edge snd_hda_intel
NMI: 15 25 22 14 Non-maskable interrupts
rtirq prioritizes the following IRQ's by default using a simple pattern matching method. This will result in elevating the realtime priority of any interrupt containing the string "snd" (in the above example it will match snd_hda_intel)
/etc/sysconfig/rtirq
. . # IRQ thread service names # (space separated list, from higher to lower priority). RTIRQ_NAME_LIST="rtc snd i8042" . .
You can check the priorities by issuing the following command. This output is based on a machine with an onboard HDA intel sound device using the default rtirq settings:
sudo service rtirq status
PID CLS RTPRIO NI PRI %CPU STAT COMMAND
511 FF 70 - 110 0.0 S irq/45-snd_hda_
44 FF 50 - 90 0.0 S irq/9-acpi
67 FF 50 - 90 0.8 S irq/41-ahci
79 FF 50 - 90 0.0 S irq/16-ehci_hcd
81 FF 50 - 90 0.0 S irq/23-ehci_hcd
82 FF 50 - 90 0.0 S irq/19-xhci_hcd
83 FF 50 - 90 0.0 S irq/12-i8042
84 FF 50 - 90 0.0 S irq/1-i8042
88 FF 50 - 90 0.0 S irq/8-rtc0
184 FF 50 - 90 0.1 S irq/42-i915
498 FF 50 - 90 0.0 S irq/44-mei
570 FF 50 - 90 0.0 S irq/17-ath9k
877 FF 50 - 90 0.0 S irq/43-p5p1
3 TS - 0 19 0.3 S ksoftirqd/0
10 TS - 0 19 0.2 S ksoftirqd/1
14 TS - 0 19 0.2 S ksoftirqd/2
18 TS - 0 19 0.1 S ksoftirqd/3
22 TS - 0 19 0.0 S ksoftirqd/4
26 TS - 0 19 0.0 S ksoftirqd/5
30 TS - 0 19 0.0 S ksoftirqd/6
34 TS - 0 19 0.1 S ksoftirqd/7
If you use other devices you prioritize them by inserting a matching string in RTIRQ_NAME_LIST after rtc. For example, RTIRQ_NAME_LIST="rtc usb2 snd i8042" could be used to match a USB class complaint device on USB bus 2, or RTIRQ_NAME_LIST="rtc firewire_ohci snd i8042" to match a firewire_ohci or firewire_core device interrupt
realTimeConfigQuickScan
realTimeConfigQuickScan is a utility which inspects the realtime capabilities of your system. If any errors are found it suggests methods to rectify the problem.
As root:
yum install realTimeConfigQuickScan
realTimeConfigQuickScan has both text and grpahical user interfaces. Either select QuickScan from your desktop menu or run realTimeConfigQuickScan from the terminal.
An example using an untuned system. This machine has an onboard intel sound device on IRQ 45
$ SOUND_CARD_IRQ=45 realTimeConfigQuickScan == GUI-enabled checks == Checking if you are root... no - good Checking filesystem 'noatime' parameter... found - warning / does not have the 'noatime' parameter set /mnt/rawhide does not have the 'noatime' parameter set /home does not have the 'noatime' parameter set For more information, see http://wiki.linuxmusicians.com/doku.php?id=system_configuration#filesystems Checking CPU Governors... CPU 0: 'ondemand' CPU 1: 'ondemand' CPU 2: 'ondemand' CPU 3: 'ondemand' CPU 4: 'ondemand' CPU 5: 'ondemand' CPU 6: 'ondemand' CPU 7: 'ondemand' - 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... 60 - not good ** vm.swappiness is larger than 10 set it with '/sbin/sysctl -w vm.swappiness=10' See also: http://linuxmusicians.com/viewtopic.php?f=27&t=452&start=30#p8916 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.linuxmusicians.com/doku.php?id=system_configuration#sysctl.conf Checking access to the high precision event timer... not readable - not good /dev/hpet found, but not readable. make /dev/hpet readable by the 'audio' group For more information, see http://wiki.linuxmusicians.com/doku.php?id=system_configuration#hpet Checking access to the real-time clock... not readable - not good /dev/rtc found, but not readable. make /dev/rtc readable by the 'audio' group For more information, see http://wiki.linuxmusicians.com/doku.php?id=system_configuration#real-time_clock Checking whether you're in the 'audio' group... yes - good Checking for multiple 'audio' groups... no - good chrt: failed to set pid 0's policy: Operation not permitted Checking the ability to prioritize processes with chrt... no - not good Could not assign a 80 rtprio value. Set up limits.conf. For more information, see http://wiki.linuxmusicians.com/doku.php?id=system_configuration#limits.conf 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.linuxmusicians.com/doku.php?id=system_configuration#installing_a_real-time_kernel Checking if kernel system timer is set to 1000 hz... found - good 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.linuxmusicians.com/doku.php?id=system_configuration#tmpfs - http://lowlatency.linuxaudio.org
An example of a fully tuned system. This system uses threadirqs rather than PREEMPT_RT kernel and has a USB class compliant device on USB bus 2 (thus the shared IRQ warning)
== GUI-enabled checks == Checking if you are root... no - good Checking filesystem 'noatime' parameter... - good Checking CPU Governors... CPU 0: 'performance' CPU 1: 'performance' CPU 2: 'performance' CPU 3: 'performance' - good Checking swappiness... 10 - good Checking for resource-intensive background processes... none found - good Checking checking sysctl inotify max_user_watches... >= 524288 - good Checking access to the high precision event timer... readable - good Checking access to the real-time clock... readable - good Checking whether you're in the 'audio' group... yes - good Checking for multiple 'audio' groups... no - good yes - 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.linuxmusicians.com/doku.php?id=system_configuration#installing_a_real-time_kernel Checking if kernel system timer is set to 1000 hz... found - good Checking kernel support for tickless timer... found - good == Other checks == Checking filesystem types... ok. ok. ** multiple devices found at the sound cards' IRQ
CPU Performance Governing
Fedora uses cpupower rather than cpufreq-set as quoted in the realTimeConfigQuickScan output.
To set your CPU Governors to performance, edit /etc/sysconfig/cpupower to read:
# See 'cpupower help' and cpupower(1) for more info CPUPOWER_START_OPTS="frequency-set -g performance" CPUPOWER_STOP_OPTS="frequency-set -g ondemand"