Messages in this thread | | | Date | Sat, 08 Apr 2006 10:11:04 +1000 | From | Peter Williams <> | Subject | Re: RT task scheduling |
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Ingo Molnar wrote: > * Darren Hart <darren@dvhart.com> wrote: > >> My last mail specifically addresses preempt-rt, but I'd like to know >> people's thoughts regarding this issue in the mainline kernel. Please >> see my previous post "realtime-preempt scheduling - rt_overload >> behavior" for a testcase that produces unpredictable scheduling >> results. > > the rt_overload feature i intend to push upstream-wards too, i just > didnt separate it out of -rt yet. > > "RT overload scheduling" is a totally orthogonal mechanism to the SMP > load-balancer (and this includes smpnice too) that is more or less > equivalent to having a 'global runqueue' for real-time tasks, without > the SMP overhead associated with that. If there is no "RT overload" [the > common case even on Linux systems that _do_ make use of RT tasks > occasionally], the new mechanism is totally inactive and there's no > overhead. But once there are more RT tasks than CPUs, the scheduler will > do "global" decisions for what RT tasks to run on which CPU.
Is this good enough? Isn't it possible with the current try_to_wake_up() implementation (with or without smpnice) for two RT tasks to end up on the same CPU even when there are less RT tasks than CPUs?
> To put even > less overhead on the mainstream kernel, i plan to introduce a new > SCHED_FIFO_GLOBAL scheduling policy to trigger this behavior. [it doesnt > make much sense to extend SCHED_RR in that direction.]
I wouldn't have thought a new policy was necessary. Why not just do this for all SCHED_FIFO (or even all RT) tasks?
BTW Does any body in the real world actually use SCHED_RR?
Peter -- Peter Williams pwil3058@bigpond.net.au
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