Re: [PATCH] sched_ext: Print deprecation warnings only once

[Andrea Righi <arighi@nvidia.com>]

Hi Breno and Christian,

On Tue, Jun 23, 2026 at 04:45:55PM +0100, Christian Loehle wrote:
> On 6/23/26 15:38, Breno Leitao wrote:
> > The deprecation notices for direct p->scx.slice/dsq_vtime writes and for
> > ops->cpu_acquire/release() use plain pr_warn(), so they repeat on every
> > scheduler (re)load and flood the kernel log.
> > > The slice/dsq_vtime notice is emitted from the BPF verifier's
> > btf_struct_access callback, which runs once per write access and is
> > re-evaluated as the verifier explores paths, so loading a single
> > scheduler can print it several times. The cpu_acquire/release notice is
> > printed on every scheduler enable.
> > 
> > Switch both to pr_warn_once() so each deprecation is reported a single
> > time, and add the missing newline to the slice/dsq_vtime message.
> 
> I guess this should be warned for once per BPF scheduler like
> sch->warned_deprecated_rq

Yeah, I agree. The thing is that we can load multiple different BPF schedulers,
and we'd want to get these messages for each of them. So ideally we need
something like sch->warned_deprecated_rq.

Thanks,
-Andrea

> 
> > 
> > Signed-off-by: Breno Leitao <leitao@debian.org>
> > ---
> >  kernel/sched/ext/ext.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
> > index 691d53fe0f648..708eb9024cb25 100644
> > --- a/kernel/sched/ext/ext.c
> > +++ b/kernel/sched/ext/ext.c
> > @@ -6988,7 +6988,7 @@ static int validate_ops(struct scx_sched *sch, const struct sched_ext_ops *ops)
> >  	 * run past the BPF allocation. Skip for cid-form.
> >  	 */
> >  	if (!sch->is_cid_type && (ops->cpu_acquire || ops->cpu_release))
> > -		pr_warn("ops->cpu_acquire/release() are deprecated, use sched_switch TP instead\n");
> > +		pr_warn_once("ops->cpu_acquire/release() are deprecated, use sched_switch TP instead\n");
> >  
> >  	/*
> >  	 * Sub-scheduler support is tied to the cid-form struct_ops. A sub-sched
> > @@ -7806,7 +7806,7 @@ static int bpf_scx_btf_struct_access(struct bpf_verifier_log *log,
> >  		     off + size <= offsetofend(struct task_struct, scx.slice)) ||
> >  		    (off >= offsetof(struct task_struct, scx.dsq_vtime) &&
> >  		     off + size <= offsetofend(struct task_struct, scx.dsq_vtime))) {
> > -			pr_warn("sched_ext: Writing directly to p->scx.slice/dsq_vtime is deprecated, use scx_bpf_task_set_slice/dsq_vtime()");
> > +			pr_warn_once("sched_ext: Writing directly to p->scx.slice/dsq_vtime is deprecated, use scx_bpf_task_set_slice/dsq_vtime()\n");
> >  			return SCALAR_VALUE;
> >  		}
> >  
> > 
> > ---
> > base-commit: 4e5dfb7c84012007c3c7061126491bbc92d71bf1
> > change-id: 20260623-scx_warning-0df49c442afb
> > 
> > Best regards,
>