scx: Prepare for BPF DSQ iterator

include/linux/sched/ext.h

@@ -51,13 +51,15 @@ enum scx_dsq_id_flags {
 };
 
 /*
- * Dispatch queue (dsq) is a simple FIFO which is used to buffer between the
- * scheduler core and the BPF scheduler. See the documentation for more details.
+ * A dispatch queue (DSQ) can be either a FIFO or p->scx.dsq_vtime ordered
+ * queue. A built-in DSQ is always a FIFO. The built-in local DSQs are used to
+ * buffer between the scheduler core and the BPF scheduler. See the
+ * documentation for more details.
  */
 struct scx_dispatch_q {
 	raw_spinlock_t		lock;
-	struct list_head	fifo;	/* processed in dispatching order */
-	struct rb_root_cached	priq;	/* processed in p->scx.dsq_vtime order */
+	struct list_head	list;	/* tasks in dispatch order */
+	struct rb_root		priq;	/* used to order by p->scx.dsq_vtime */
 	u32			nr;
 	u64			id;
 	struct rhash_head	hash_node;
@@ -119,18 +121,20 @@ enum scx_kf_mask {
 	__SCX_KF_TERMINAL	= SCX_KF_ENQUEUE | SCX_KF_SELECT_CPU | SCX_KF_REST,
 };
 
+struct scx_dsq_node {
+	struct list_head	list;		/* dispatch order */
+	struct rb_node		priq;		/* p->scx.dsq_vtime order */
+	u32			flags;		/* SCX_TASK_DSQ_* flags */
+};
+
 /*
  * The following is embedded in task_struct and contains all fields necessary
  * for a task to be scheduled by SCX.
  */
 struct sched_ext_entity {
 	struct scx_dispatch_q	*dsq;
-	struct {
-		struct list_head	fifo;	/* dispatch order */
-		struct rb_node		priq;	/* p->scx.dsq_vtime order */
-	} dsq_node;
+	struct scx_dsq_node	dsq_node;	/* protected by dsq lock */
 	u32			flags;		/* protected by rq lock */
-	u32			dsq_flags;	/* protected by dsq lock */
 	u32			weight;
 	s32			sticky_cpu;
 	s32			holding_cpu;

init/init_task.c

@@ -101,7 +101,7 @@ struct task_struct init_task __aligned(L1_CACHE_BYTES) = {
 #endif
 #ifdef CONFIG_SCHED_CLASS_EXT
 	.scx		= {
-		.dsq_node.fifo	= LIST_HEAD_INIT(init_task.scx.dsq_node.fifo),
+		.dsq_node.list	= LIST_HEAD_INIT(init_task.scx.dsq_node.list),
 		.flags		= 0,
 		.sticky_cpu	= -1,
 		.holding_cpu	= -1,

kernel/sched/core.c

@@ -4586,7 +4586,7 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
 
 #ifdef CONFIG_SCHED_CLASS_EXT
 	p->scx.dsq		= NULL;
-	INIT_LIST_HEAD(&p->scx.dsq_node.fifo);
+	INIT_LIST_HEAD(&p->scx.dsq_node.list);
 	RB_CLEAR_NODE(&p->scx.dsq_node.priq);
 	p->scx.flags		= 0;
 	p->scx.weight		= 0;