Low latency for audio applications

Posted Jan 27, 2005 10:55 UTC (Thu) by farnz (subscriber, #17727)
In reply to: Low latency for audio applications by xorbe
Parent article: Low latency for audio applications

It is rocket science; if his app exceeds 100% CPU usage, he's not getting what he wants, and there's nothing a better kernel can do about it. As exceeding 100% CPU is going to lock up his machine, the patch allows a musician to set a limit, and then if his realtime applications are going to lock his machine up, the kernel drops their realtimeness, thus giving a musician a chance of recovering. Without this mechanism, the machine can lock hard, and there's no way to discover why, or to recover.

As a simple example of when this helps; a soft synth is normally a realtime application (MIDI in -> Waveform out). When running, a soft synth doesn't take that much CPU; if it did, it wouldn't work. If your algorithm fails, and causes the synth to run away in an endless loop (bad validation of input MIDI data, for example), you're doomed if it can take 100% CPU. If all your RT tasks are limited to 95% CPU between them, you can fire up "top", notice that the soft synth has gone from around 5% CPU to around 90% CPU, and kill it.