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

[From: Eero Tamminen]

Hi,

ext tarantism wrote:
> On Mon, 2010-04-26 at 16:19 +0300, Eero Tamminen wrote:
>> ext tarantism wrote:
>>> _POSIX_PRIORITY_SCHEDULING is defined but attempting to create a pthread
>>> with SCHED_FIFO returns an error. Calling pthread_setschedparam with
>>> policy of SCHED_FIFO doesn't complain but checking with
>>> pthread_getschedparam shows a policy of SCHED_OTHER.
>>>
>>> Is it possible to set a policy of SCHED_FIFO (or SCHED_RR) or am I
>>> wasting my time?
>> Are you running as root?
> 
> Thanks for the reply.
> Yes, I'm running as root.
> Code that works fine on Ubuntu returns an error from pthread_create.
> Can you confirm that SCHED_FIFO works on Fremantle? If it does, I'll
> happily keep plugging away but it would be nice to know that what I'm
> trying to do is possible!

There's a stress-test package that has a tool with options
for selecting the scheduler:
http://repository.maemo.org/pool/maemo5.0/free/s/sp-stress/

Changing the scheduler doesn't for some reason seem to work now:
---------
# cpuload -s f 10
 

CPU load generator, build Sep  4 2009 15:09:38. 

Copyright (C) 2006,2008 Nokia Corporation. 

 

WARNING: setting scheduler failed failed: operating with default. 

Reason: Operation not permitted
...
# strace cpuload -s f 10 
 
           ...
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.

Maybe the issues is with the used realtime priority:
---------
# cat /proc/self/limits |grep realtime
Max realtime priority     0                    0 

Max realtime timeout      unlimited            unlimited            us
---------

Does setting SCHED_FIFO with priority 0 work?


	- Eero