Re: [RFC PATCH 0/6] Convert all tasklets to workqueues

[Ingo Molnar <mingo@elte.hu>]

* Daniel Walker <dwalker@mvista.com> wrote:

> >  - tasklets have certain fairness limitations. (they are executed in
> >    softirq context and thus preempt everything, even if there is 
> >    some potentially more important, high-priority task waiting to be 
> >    executed.)
> 
> Since -rt has been executing tasklets in process context for a long 
> time, I'm not sure this change would cause to many regressions. 
> However, it seems like implicit dependencies on "tasklets preempt 
> everything" might crop up. The other issue is if they don't "preempt 
> everything" (most of the time), what default priority do we give them 
> (all of the time)? [...]

there is no such guarantee at all (of 'instant preemption'), even with 
current, softirq-based tasklets. A tasklet might be 'stolen' by another 
CPU. It might be delayed to the next timer tick (or other softirq 
execution). Or it might be delayed into a ksoftirqd context, which 
currently runs at nice +19. So your worry of implicit execution 
dependencies is unfounded, because, if they existed, they would be bad 
(and triggerable) bugs today too.

	Ingo