[maemo-developers] Is it possible to use SCHED_FIFO policy on N900?

[From: Kai.Vehmanen at nokia.com]

Hi,

On 27 April 2010, Tamminen Eero (Nokia-D/Helsinki) wrote:
>sched_get_priority_max(SCHED_FIFO)      = 99
>
>sched_setscheduler(0, SCHED_FIFO, { 99 }) = -1 EPERM (Operation not
>permitted)
[...]
>But it definitely worked last summer when this option was added to it.
>I'm not sure what's happened in the meanwhile.

the resource management framework is coordinating use
of POSIX real-time scheduling policies and rejecting
requests from apps that are not whitelisted (with help of 
the kernel).

This makes sense as user-space use of SCHED_FIFO/RR needs
to be carefully managed system-wide, or you can seriously screw
up key functions of the device (e.g. making calls, playing
audio).

I'm not sure what's the easiest way to work around this (not
working in this area), but e.g. with a custom kernel, and/or 
removing the resource management components, will certainly do 
the trick. But in many/most cases, and especially for applications 
intended for wider use (i.e. not just running N900 devices 
customized for some special-purpose), I'd recommend against it.

Br,
-- 
Kai Vehmanen