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SubjectRe: Network slowdown due to CFS

* Jarek Poplawski <> wrote:

> > firstly, there's no notion of "timeslices" in CFS. (in CFS tasks
> > "earn" a right to the CPU, and that "right" is not sliced in the
> > traditional sense) But we tried a conceptually similar thing [...]
> >From kernel/sched_fair.c:
> "/*
> * Targeted preemption latency for CPU-bound tasks:
> * (default: 20ms, units: nanoseconds)
> *
> * NOTE: this latency value is not the same as the concept of
> * 'timeslice length' - timeslices in CFS are of variable length.
> * (to see the precise effective timeslice length of your workload,
> * run vmstat and monitor the context-switches field)
> ..."
> So, no notion of something, which are(!) of variable length, and which
> precise effective timeslice lenght can be seen in nanoseconds? (But
> not timeslice!)

You should really read and understand the code you are arguing about :-/

In the 2.6.22 scheduler, there was a p->time_slice per task variable
that could be manipulated. (Note, in 2.6.22's sched_yield() did not
manipulate p->time_slice.)

sysctl_sched_latency on the other hand is not something that is per task
(it is global) so there is no pending timeslice to be "cleared" as it
has been suggested naively.

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