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Realtime group scheduling doesn't know JACK

Jan 11, 2011, 14:32 (0 Talkback[s])
(Other stories by Jonathan Corbet)


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"Realtime scheduling for audio applications (or the lack thereof) has been a recurring theme over a number of years. LWN last visited this issue in 2009, when the addition of rtkit was put forward as the (pulseaudio-based) solution for casual audio use. Serious audio users - those using frameworks like JACK - have always wanted more direct access to realtime scheduling, though. That access has, for some years, been provided through resource limits. Now it seems that a feature merged for the 2.6.25 kernel is, two years later, beginning to cause grief for some JACK users. The resulting discussion is an interesting illustration of technical differences, how long it can take for new features to filter through to users, and how one should best deal with the kernel development community.

"The combination of the RLIMIT_RTPRIO and RLIMIT_RTTIME resource limits allows the system administrator to give specific users the ability to run tasks with realtime priority for a bounded period of time. The feature is easily configured in /etc/security/limits.conf and will prevent casual users from locking up the system with a runaway realtime process. This feature is limited in its flexibility, though, and is relatively easy to circumvent, so it has never been seen as an ideal solution."

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