Mon, 15 Jan 2001 Bernhard Kuhn wrote:
[...]
> "rt" just places itself into SCHED_FIFO - like
> David Olofson already explained - and then calls
Please not that you also need the lowlatency patch to geuarantee scheduling
latencies below 1 ms for SCHED_FIFO. SCHED_FIFO alone *does not* protect you
from occasional latency peaks of 100 ms or worse under heavy system load; it's
just a way of bypassing all other _user space_ tasks - not the lengthy kernel
operations that the lowlatency patch addresses.
> the given command that will run in the same scheduling
> space. This means, you can virtualy run any program in
> Posix-Realtime-space even when it isn't designed
> for doing so. For me, this works fine using an
> Nvidia 2GTS based card (with NVdriver) and
> several 3D-games :-)
I haven't tried running games as SCHED_FIFO yet - nice to know that it works
most of the time! (The average X application will eventually freeze, or even
worse, freeze X eventually in my experience.)
> But beware: ensure that the X-Server and the
> Window-Manager are running with a higher
> priority as the 3D-program, because otherwise,
> the computer might easyly seem to be freezed:
> the machine is rather busy with
> redrawing the 3D-application, but doesn't get
> any new input from the X-Server/Window-Manager,
> because these processes are never scheduled any
> more)
Yep, that's one of the problems, and as X and normal X applications aren't even
designed for 100% CPU utilization - let alone being guaranteed to really get
that - there will be problems with some of them.
> Also, having a bash running with the
> highest priority located on a serial terminal
> is basicaly a good idea when using the
> command "rt", to have a backdoor in case
> the X-Server loops :-)
"Manual RT Watchdog" :-)
I was going to write a more automated solution (a real watchdog for SCHED_FIFO
threads), but haven't had the time yet. It's really meant as a service for
applications that explicitly use SCHED_FIFO for RT processing, but could of
course be used as a complement to the RT command.
//David
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