* Darren Hart <darren@xxxxxxxxxx> 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.
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.]