Re: [RFC PATCH] sched/deadline: Avoid dl_server boosting with expired deadline

[Peter Zijlstra]

On Fri, Oct 31, 2025 at 04:41:22PM +0100, Gabriele Monaco wrote:
> On Fri, 2025-10-31 at 16:20 +0100, Peter Zijlstra wrote:
> > On Fri, Oct 31, 2025 at 02:24:17PM +0100, Gabriele Monaco wrote:
> > > 
> > > Different scenario if I have the CPU busy with other tasks (e.g. RT
> > > policies), there I can see the server stopping and starting again.
> > > After I do this I seem to get a different behaviour (even some boosting
> > > after idle), I'm trying to understand what's going on.
> > > 
> 
> After running some heavy RT workload (stress-ng --cpu 10 --sched rr) I do see
> the server stopping and starting as the models would expect, but somehow it's
> always boosting as soon as it's started.
> 
> Apparently dl_defer_running is always 1 in that scenario. Perhaps running idle
> counts as running something too, so it never defers. But I can't really see how
> this happens..

The transition [4], will retain dl_defer_running, such that a timely
re-start of the dl_server can immediately run again.