Re: [PATCH sched_ext/for-7.1] sched_ext: Documentation: Add ops.dequeue() to task lifecycle

[Andrea Righi <arighi@nvidia.com>]

Hi Emil,

On Mon, Apr 06, 2026 at 10:49:18AM -0400, Emil Tsalapatis wrote:
> On Mon Apr 6, 2026 at 7:47 AM EDT, Andrea Righi wrote:
> > Document ops.dequeue() in the sched_ext task lifecycle now that its
> > semantics are well-defined.
> >
> > Also update the pseudo-code to use task_is_runnable() consistently and
> > clarify the case where ops.dispatch() does not refill the time slice.
> >
> > Fixes: ebf1ccff79c4 ("sched_ext: Fix ops.dequeue() semantics")
> 
> Is the Fixes: tag appropriate here? It's not like the original patch
> introduced a bug by fixing ops.dequeue().

Yeah, the intent here was to make sure this commit isn't applied without
ebf1ccff79c4 (otherwise the state machine would be inaccurate), but that
shouldn't happen, so it's probably reasonable to drop the Fixes line.

Thanks,
-Andrea

> 
> Otherwise the state machine looks fine to me!
> 
> Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
> 
> > Signed-off-by: Andrea Righi <arighi@nvidia.com>
> > ---
> >  Documentation/scheduler/sched-ext.rst | 24 +++++++++++++++---------
> >  1 file changed, 15 insertions(+), 9 deletions(-)
> >
> > diff --git a/Documentation/scheduler/sched-ext.rst b/Documentation/scheduler/sched-ext.rst
> > index 404b4e4c33f7e..9f03650abfeba 100644
> > --- a/Documentation/scheduler/sched-ext.rst
> > +++ b/Documentation/scheduler/sched-ext.rst
> > @@ -422,23 +422,29 @@ by a sched_ext scheduler:
> >  
> >          ops.runnable();         /* Task becomes ready to run */
> >  
> > -        while (task is runnable) {
> > +        while (task_is_runnable(task)) {
> >              if (task is not in a DSQ && task->scx.slice == 0) {
> >                  ops.enqueue();  /* Task can be added to a DSQ */
> >  
> > -                /* Any usable CPU becomes available */
> > +                /* Task property change (i.e., affinity, nice, etc.)? */
> > +                if (sched_change(task)) {
> > +                    ops.dequeue(); /* Exiting BPF scheduler custody */
> > +                    continue;
> > +                }
> > +            }
> >  
> > -                ops.dispatch(); /* Task is moved to a local DSQ */
> > +            /* Any usable CPU becomes available */
> > +
> > +            ops.dispatch();     /* Task is moved to a local DSQ */
> > +            ops.dequeue();      /* Exiting BPF scheduler custody */
> >  
> > -                ops.dequeue(); /* Exiting BPF scheduler */
> > -            }
> >              ops.running();      /* Task starts running on its assigned CPU */
> >  
> > -            while task_is_runnable(p) {
> > -                while (task->scx.slice > 0 && task_is_runnable(p))
> > -                    ops.tick();     /* Called every 1/HZ seconds */
> > +            while (task_is_runnable(task) && task->scx.slice > 0) {
> > +                ops.tick();     /* Called every 1/HZ seconds */
> >  
> > -                ops.dispatch();     /* task->scx.slice can be refilled */
> > +                if (task->scx.slice == 0)
> > +                    ops.dispatch(); /* task->scx.slice can be refilled */
> >              }
> >  
> >              ops.stopping();     /* Task stops running (time slice expires or wait) */
>