Re: [Xen-devel] [PATCH] Getting and setting SEDF scheduling parameters

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

> Note that this patch makes strong assumptions about how the scheduling 
> parameters are used.  So, I recommend someone take a really close look at 
> my comments to make sure I've preserved the Xen team's intentions for how 
> the SEDF scheduler works. :-)

I think that the current GET/PUT_INFO call is definitely screwed. The
intended use of extratime should be to allow time-driven domains to
get a best-effort weighted slice of otherwise-idle cpu. Extratime is
not a completely separate scheduling category in its own right! :-)

The scheduling logic should be something like: (a) schedule runnable
time-driven domains with time slice left; then (b) schedule runnable
weight-driven domains; then (c) schedule extratime-aware time-driven
domains. Apart from this there is a bunch of scheduler complexity to
try and sanely handle I/O workloads (short-blocking domains).

Depending on how unused time slices are divvied up, it may make sense
to allow real-time-weight-driven domains also to specify
extratime-awareness (depends on whether real-time weights divvy up all
available cpu (non-time-sliced and unused time-sliced), or just the
spare non-time-sliced time according to the predetermined schedule).

 -- Keir

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