Revision as of 08:50, 27 March 2008 by Billhuey
Grand Unified Scheduler Project
Questions I'm pondering:
EDF = earlier deadline first
HRT = hard real time
SRT = soft real time
BE = best effort
- How does a static priority system like Linux express itself in terms of an EDF scheduler ? How do things like hardness in a SCHED_FIFO task map to in EDF ? Some task are burst driven but lags or differing isn't considered a failure. How would a task like that be handled by EDF or variant ?
- Is M-CASH, EDF-HSB etc... flexible enough as an abstract container or common factor mathematically or algorithmically so that all three stock scheduler policies, SCHED_FIFO, SCHED_RR and SCHED_OTHER (CFS) can be constructed in terms of that algorithm ?
- If these algorithms overlook the problem of aperiodic overloads, then what kind of overload handling can we do ? apply what we have already with the current rt-overload logic where we scan run queues across the system (or possibly with a specific CPU set) to migrate a task to another CPU that isn't running a real time task (SCHED_FIFO/RR) ? What about the use of a cheaply precomputed slack span that can be quickly read during a cross processor run queue scan to find a suitable BE slot span to handle an overload migration ? Let's call this EDF overload (rebalancing).
- How cheap is it to compute or pre-compute a span of slack slots for BE threads like irq-threads ?
- How would a practical EDF system look like with overload code ? Have EDF be largely run queue localized with manual assignments and with an overload condition for softer jobs ?