[linux-audio-dev] kernel preemption patch and 2.4.19

[Roger Larsson]

On Wednesday 02 June 2004 22.13, Michael Ost wrote:
> What specific benefits have folks seen by turning on the kernel
> preemption patch in a 2.4.19 kernel?

2.4 series is not really built for preemption. But...

>
> We found that a nasty system crash was fixed by turning off preemption.
> The crash would happen fairly reliably by switching between virtual
> terminals a number of times. It locked up the system hard. So hard that
> we can't really find the problem in the kernel; we just found a
> work-around basically by trial and error.

Do you use a SMP computer? If not then you might have run into something
that could hurt a SMP computer running without preemption...

(Running SMP and preemption is kind of weird. And you may run into additional
problems - per CPU data has also to be protected by spinlocks, etc... )

>
> We turned on kernel preemption basically because "everyone was doing
> it". We haven't noticed any obvious, serious problems or differences
> since turning preemption off.
>
> Does anyone have some suggestions about what differences to expect and
> what we might have a closer look at?

You won't notice much difference unless you run real time processes. But they
will need to be suid root (or some wrapper/helper) to become RT processes,
and many kernels do not ship with multimedia stuff suid...

>
> Also, we are newbies about reporting this kind of crash. Any clues about
> where to report it or ask about it?

First - you mention virtual terminals
	What video driver are you using? Nvidia?
	If that is the case retest with xfree86 (nv)

Second - try to what is happening (Magic SysRq)

Third - 2.4.19 is kind of old now (not that many will be interested...), 
upgrade and try to reproduce.

/RogerL

-- 
Roger Larsson
Skellefteå
Sweden