[PATCH] sched_ext: optimize sched_ext_entity layout for cache locality

[David Carlier <devnexen@gmail.com>]

Reorder struct sched_ext_entity to place ops_state, ddsp_dsq_id, and
ddsp_enq_flags immediately after dsq. These fields are accessed together
in the do_enqueue_task() and finish_dispatch() hot paths but were
previously spread across three different cache lines. Grouping them on
the same cache line reduces cache misses on every enqueue and dispatch
operation.

Signed-off-by: David Carlier <devnexen@gmail.com>
---
 include/linux/sched/ext.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched/ext.h b/include/linux/sched/ext.h
index bcb962d5ee7d..80e70a9642fd 100644
--- a/include/linux/sched/ext.h
+++ b/include/linux/sched/ext.h
@@ -162,6 +162,9 @@ struct scx_dsq_list_node {
  */
 struct sched_ext_entity {
 	struct scx_dispatch_q	*dsq;
+	atomic_long_t		ops_state;
+	u64			ddsp_dsq_id;
+	u64			ddsp_enq_flags;
 	struct scx_dsq_list_node dsq_list;	/* dispatch order */
 	struct rb_node		dsq_priq;	/* p->scx.dsq_vtime order */
 	u32			dsq_seq;
@@ -173,7 +176,6 @@ struct sched_ext_entity {
 	s32			selected_cpu;
 	u32			kf_mask;	/* see scx_kf_mask above */
 	struct task_struct	*kf_tasks[2];	/* see SCX_CALL_OP_TASK() */
-	atomic_long_t		ops_state;
 
 	struct list_head	runnable_node;	/* rq->scx.runnable_list */
 	unsigned long		runnable_at;
@@ -181,8 +183,6 @@ struct sched_ext_entity {
 #ifdef CONFIG_SCHED_CORE
 	u64			core_sched_at;	/* see scx_prio_less() */
 #endif
-	u64			ddsp_dsq_id;
-	u64			ddsp_enq_flags;
 
 	/* BPF scheduler modifiable fields */
 
-- 
2.51.0