sched_ext: Compact struct bpf_iter_scx_dsq_kern

struct scx_iter_scx_dsq is defined as 6 u64's and scx_dsq_iter_kern was
using 5 of them. We want to add two more u64 fields but it's better if we do
so while staying within scx_iter_scx_dsq to maintain binary compatibility.

The way scx_iter_scx_dsq_kern is laid out is rather inefficient - the node
field takes up three u64's but only one bit of the last u64 is used. Turn
the bool into u32 flags and only use the lower 16 bits freeing up 48 bits -
16 bits for flags, 32 bits for a u32 - for use by struct
bpf_iter_scx_dsq_kern.

This allows moving the dsq_seq and flags fields of bpf_iter_scx_dsq_kern
into the cursor field reducing the struct size by a full u64.

No behavior changes intended.

Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 9 insertions, 1 deletions

diff --git a/include/linux/sched/ext.h b/include/linux/sched/ext.h
index dc646cca4fcf..1ddbde64a31b 100644
--- a/include/linux/sched/ext.h
+++ b/include/linux/sched/ext.h
@@ -119,9 +119,17 @@ enum scx_kf_mask {
 	__SCX_KF_TERMINAL	= SCX_KF_ENQUEUE | SCX_KF_SELECT_CPU | SCX_KF_REST,
 };
 
+enum scx_dsq_lnode_flags {
+	SCX_DSQ_LNODE_ITER_CURSOR = 1 << 0,
+
+	/* high 16 bits can be for iter cursor flags */
+	__SCX_DSQ_LNODE_PRIV_SHIFT = 16,
+};
+
 struct scx_dsq_list_node {
 	struct list_head	node;
-	bool			is_bpf_iter_cursor;
+	u32			flags;
+	u32			priv;		/* can be used by iter cursor */
 };
 
 /*