Re: High resolution timers and BH processing on -RT

[Ingo Molnar <mingo@elte.hu>]

* Thomas Gleixner <tglx@linutronix.de> wrote:

> > or is it that we have a 'group' of normal timers expiring, which, if
> > they happen to occur _just_ prior a HRT event will generate a larger
> > delay?
> 
> Yep. The timers expire at random times. So it's likely to have short
> sequences of timer interrupts going off. This needs reprogramming of
> the PIT and processing of the expired timers.

i dont really like the static splitup of 'normal' vs. 'HRT' timers -
there might in fact be separate priority requirements between HRT timers
too.

i think one possible solution would be to introduce some notion of
'timer priority', and to expire each timer priority level in a separate
timer expiry thread. Priority 0 (lowest) would be expired in ksoftirqd,
and there would be 3 separate threads for say priorities 1-3. Or
something like this. Potentially exposed to user-space as well, via new
APIs. Hm?

To push this even further: in theory timers could inherit the priority
of the task that starts them, and they would be expired in that priority
order - but this probably needs a pretty clever (and most likely
complex) data-structure ...

	Ingo