Re: [PATCH v2] sched/deadline: Make dl-server nohz full aware

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Oct 01, 2026 at 04:27:36PM +0200, Peter Zijlstra wrote:

> >  bool sched_can_stop_tick(struct rq *rq)
> >  {
> >  	/* Deadline tasks, even if single, need the tick */
> >  	if (rq->dl.dl_nr_running)
> >  		return false;
> >  
> >  	/*
> > +	 * If there are RT tasks, we may need the tick (for >1 RR tasks),
> > +	 * but we must also service lower-priority CFS/SCX tasks via dl-servers.
> >  	 */
> > +	if (rq->rt.rt_nr_running) {
> > +		bool cfs_or_scx_queued = false;
> > +
> > +		if (rq->cfs.h_nr_queued) {
> > +			dl_server_start(&rq->fair_server);
> > +			cfs_or_scx_queued = true;
> > +		}
> > +#ifdef CONFIG_SCHED_CLASS_EXT
> > +		if (rq->scx.nr_running) {
> > +			dl_server_start(&rq->ext_server);
> > +			cfs_or_scx_queued = true;
> > +		}
> > +#endif
> > +		if (cfs_or_scx_queued)
> >  			return false;

What the purpose of this boolean, both true assignments above can simply
be return false, no?

> >  
> > +		/*
> > +		 * Only RT tasks, no CFS/SCX. Stop servers to prevent spurious

No DL either, you've filtered those out above.

> > +		 * wakeups. Tick can stop for single RR or any FIFO, but must
> > +		 * run for multiple RR (round-robin behavior).
> > +		 */
> > +		dl_servers_stop_all(rq);
> > +		if (rq->rt.rr_nr_running > 1)
> > +			return false;
> >  		return true;
> > +	}