Subject: Re: [linux-audio-dev] jack, low latency and IO
From: Jack O'Quin (joq_AT_io.com)
Date: Tue Dec 07 2004 - 17:44:54 EET
> On tis, 2004-12-07 at 13:07 +0100, Artem Baguinski wrote:
> > I'm a bit puzzled with this one thing about low latency and jack: real
> > time bits can't do IO, but don't you get latency between say me
> > pressing some button and sound doing click? there's no garanty the not
> > realtime part of the application will run often enough to read the
> > input device, no?
Jens M Andreasen <jens.andreasen_AT_chello.se> writes:
> .. your audioapp should repaint itself before any less urgent
> process (with normal or slightly high priority) gets a chance at the
> CPU. JACK will still run at (near?) highest priority, so if your
> audio-processing demands 90% CPU there will be not so much
> repainting going on ...
As a practical matter, JACK had better *not* be using 90% of your CPU.
That sort of load is unlikely to be reliably sustainable.
For any reasonable CPU load, there should be plenty of cycles
remaining to run non-realtime threads without requiring special
scheduling hacks.
Don't forget that other system resource bottlenecks can cause poor
performance. When running realtime, JACK locks down large amounts of
memory. Your GUI code may be getting paged out.
-- joq
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