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SubjectRe: [PATCH 0/5] Fix FIFO-99 abuse
On 08/02/19 16:33, Peter Zijlstra wrote:
> > > Also also, RR-SMP is actually broken (and nobody has cared enough to
> > > bother fixing it).
> >
> > If you can give me enough pointers to understand the problem I might be able to
> > bother with it :-)
>
> So the push-pull balancer we have (designed for FIFO but also applied to
> RR) will only move a task if the destination CPU has a lower prio. In
> the case where one CPU has 3 tasks and the other 1, and they're all the
> same prio, it does nothing. For FIFO that is fine, for RR, not so much.
>
> Because then the one CPU will RR between 3 tasks, giving each task
> 1/3rd, while the other will only run the one task.

Okay so what we need to do is keep a count of number of RR tasks on each CPU
(which we already do IIRC) and take that into account in
find_loweset_rq()/cpupri_find().

Let me see if I can create a test case then hack something.

Thanks

--
Qais Yousef

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