Re: RT question : softirq and minimal user RT priority

[Steven Rostedt <rostedt@goodmis.org>]

On Fri, 2006-01-13 at 15:27 +0100, Serge Noiraud wrote:
> Hi,
> 
> 	I was testing 2.6.15-rt3. During my tests, I tried to run a program which made a loop at
> RT priority 10 and 30.

So you have two programs running, one at priority 10 and 30 right?

> I was very happy to see that after the tests, I can't use any command except those already in memory.

So, are these programs still running?  Are they in busy loops?

> My filesystems were in read-only after the test. I was unable to shutdown the machine : 

How did the filesystems go into read-only?  Did the tests do that?

> top => command not found
> <CTRL><ALT><DEL> => INIT: cannot execute "/sbin/shutdown"
> /sbin/reboot   => Input/Output error
> I had to push the reset button.

I'll need more info to understand these.

> 
> My questions are : 
> Did I find a bug ?

Don't know yet.

> Is the smallest usable real-time priority greater than the highest real-time softirq ?

Nope, you can use any rt priority you want.  It's up to you whether you
want to preempt the softirqs or not. Be careful, timers may be preempted
from delivering signals to high priority processes.  I have a patch to
fix this, but I'm waiting on input from either Thomas Gleixner or Ingo.

> In this case could we forbid priority lesser than the highest softirq priority ?

No need.

-- Steve