sched/fair: Fix NO_RUN_TO_PARITY case

EEVDF expects the scheduler to allocate a time quantum to the selected
entity and then pick a new entity for next quantum.
Although this notion of time quantum is not strictly doable in our case,
we can ensure a minimum runtime for each task most of the time and pick a
new entity after a minimum time has elapsed.
Reuse the slice protection of run to parity to ensure such runtime
quantum.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250708165630.1948751-3-vincent.guittot@linaro.org

1 files changed, 9 insertions, 1 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4802fcf738cd..55921385927d 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -583,7 +583,15 @@ struct sched_entity {
 	u64				sum_exec_runtime;
 	u64				prev_sum_exec_runtime;
 	u64				vruntime;
-	s64				vlag;
+	union {
+		/*
+		 * When !@on_rq this field is vlag.
+		 * When cfs_rq->curr == se (which implies @on_rq)
+		 * this field is vprot. See protect_slice().
+		 */
+		s64                     vlag;
+		u64                     vprot;
+	};
 	u64				slice;
 
 	u64				nr_migrations;