Partitioned Scheduling

Adam Lackorzynski adam at
Thu Sep 8 23:30:16 CEST 2016


On Mon Sep 05, 2016 at 12:49:11 +0200, Daniel Krefft wrote:
> Hi,
> if I understand it right, there is only one scheduler in the kernel
> realizing one distinct scheduling strategy (e.g. fixed prio).


> However,
> given a multi-core system, several (all) cores are using *this* strategy
> in an independent core-local style. I'm right?

Yes, exactly.

> So, the questions are:
> - How can I enhance this approach for several scheduling schemes (not
> only one)?

There's design space as there are currently no interfaces to select
between different scheduler variants. Currently, as there's only one
variant at a time right now, there are no abstractions in the kernel to
support multiple variants at the same time. That's probably the first
thing to add. But maybe it's easier to extend the current variant with
the feature you need and select those feature by adding parameters /
flags / etc. to the scheduling parameters. This interface is flexible in
a way that it supports different types of scheduling params.

> - Where does the mapping between core and scheduling scheme happen?
> (e.g. compile-time/run-time)

That's also design space but I'd say a run-time as I would assume
there's not much difference in implementation among the two.
> - Which files do I need to change?

All relevant files are in the src/kern directory and match sched*.cpp
and ready_queue_*.cpp, the schedule() function itself is in context.cpp

> Maybe you can help me to get the big picture (flow chart) of scheduling
> in Fiasco.OC because it is vital for the next steps and our research.

Scheduling is driven by the selected algorithm. For example, for the
default fixed-prio scheduler, there's an array of prios where each
element has a linked list with the ready-to-run threads. The next thread
to run is taken from the list with the highest prio that has runnable
threads. Look at ready_queue_fp.cpp and sched_context-fixed_prio.cpp.

Adam                 adam at

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