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Incomplete preemption reason enums make it difficult to analyze interactions between different schedulers, and filling this gap significantly improves observability for existing SCX workloads. > > This patch does not modify core scheduling logic, introduces zero performance overhead, and adds negligible long-term maintenance cost. Please, don't re-send a new patch just for this, at least you should add a v2 with a proper changelog. But in this case the discussion can continue in the previous email thread. Thanks, -Andrea > > sched_ext currently distinguishes preemption caused by STOP, > DL and RT scheduling classes, but preemption from the Fair > scheduler is reported as SCX_CPU_PREEMPT_UNKNOWN. > > When analyzing SCX scheduling behavior, it is useful to know > whether a task was preempted by RT/DL classes or switched out > in favor of a Fair-class task. The lack of a dedicated reason > makes debugging and observability more difficult. > > Add SCX_CPU_PREEMPT_FAIR and report it when the next scheduled > task belongs to fair_sched_class. > > This change improves scheduling diagnostics and observability > without affecting scheduling behavior. > > Signed-off-by: Cui Jian > --- > kernel/sched/ext.c | 2 ++ > kernel/sched/ext_internal.h | 2 ++ > 2 files changed, 4 insertions(+) > > diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c > index 5d2d19473a82..6e0281218197 100644 > --- a/kernel/sched/ext.c > +++ b/kernel/sched/ext.c > @@ -3015,6 +3015,8 @@ preempt_reason_from_class(const struct sched_class *class) > return SCX_CPU_PREEMPT_DL; > if (class == &rt_sched_class) > return SCX_CPU_PREEMPT_RT; > + if (class == &fair_sched_class) > + return SCX_CPU_PREEMPT_FAIR; > return SCX_CPU_PREEMPT_UNKNOWN; > } > > diff --git a/kernel/sched/ext_internal.h b/kernel/sched/ext_internal.h > index a075732d4430..3ce07bec58a5 100644 > --- a/kernel/sched/ext_internal.h > +++ b/kernel/sched/ext_internal.h > @@ -241,6 +241,8 @@ enum scx_cpu_preempt_reason { > SCX_CPU_PREEMPT_DL, > /* next task is being scheduled by &sched_class_stop */ > SCX_CPU_PREEMPT_STOP, > + /* next task is being scheduled by &sched_class_fair*/ > + SCX_CPU_PREEMPT_FAIR, > /* unknown reason for SCX being preempted */ > SCX_CPU_PREEMPT_UNKNOWN, > }; > -- > 2.34.1 >