[linux-audio-user] -rt IRQ handler priorities

[Kjetil S. Matheussen]

On Tue, 9 May 2006, Lee Revell wrote:

> On Tue, 2006-05-09 at 15:45 -0700, Kjetil S. Matheussen wrote:
>>> Hmm, it sounds like a solution could be to separate timers that just
>>> wake up a process from ones that do actual work and run them in separate
>>> kernel threads.
>>>
>>
>> I don't understand why you want that. To me (which
>> knows about nothing about how the kernel works), the solution to
>> the problem is crystal clear: The softirq timer needs to have the highest
>> priority, and the only thing the sofirq timer threads does is to
>> make sure threads that should be woken up are put into some kernel
>> schedule queue somehow. I don't understand why the softirq timer threads
>> should cause any latency problems, what does it do except scheduling
>> waiting threads?
>>
>
> Well as you have seen the softirq timer thread apparently does route
> cache flushing and a bunch of other things we don't want it to do.  I
> was under the impression these were already done by separate threads.
>
> I think we are in agreement.

Good. :-)


>  I have to double check how it works in -rt
> - I've been running mainline lately which still has a single ksoftirqd
> process.
>

I think the ksoftirqd processes have the same problem. At least for
das_watchdog, it must be set to 99 for the watchdog to work. There is
even code to check that it/they have priority 99.