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SubjectRe: real-time threaded IO with low latency (audio)
Arvind Sankar wrote:
(...)
> which was exactly Xymoron's point, I thought.
> RT requires no disk hits
> vidcapture requires lots of disk access
> hence, can't have both.

Can't have both? With RTL you can do that kind of things right now, with
timing precision better than 50 microseconds. Rock solid. Never ever a
missed deadline, no matter the load on any part of the standard Linux
system.

People are doing it already, so it's possible all right. In theory,
there's nothing stopping you from doing it with SCHED_FIFO tasks instead
of RTL tasks, but it would probably be a very big hack.

My suggestion would be to keep hard real time a separate part of the
system, but integrating it better with standard Linux, so that it
doesn't mean a completely new environment for the developer. (There's a
pthreads API, but it's still kernel modules.) I'm working on a driver
API that will make drivers work with both RTL and standard Linux (same
code, runtime selection of sync methods), and this might be usable for
all kinds of drivers that can be of interest to hard real time apps.

Scheduling mlock()ed user space tasks directly from RT context would be
the next step towards making hard realtime completely transparent to
most existing RT applications, at least on the source code level.

Comments?


//David

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