[PATCH v3 1/5] sched_ext: Implement scx_rq_clock_update/stale()

[Changwoo Min <multics69@gmail.com>]

scx_rq_clock_update() and scx_rq_clock_stale() manage the status of an
rq clock when sched_ext is enabled. scx_rq_clock_update() keeps the rq
clock in memory and its status valid. scx_rq_clock_stale() invalidates
the current rq clock not to use the cached rq clock.

Signed-off-by: Changwoo Min <changwoo@igalia.com>
---
 kernel/sched/sched.h | 48 +++++++++++++++++++++++++++++++-------------
 1 file changed, 34 insertions(+), 14 deletions(-)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 76f5f53a645f..da55b39c9e58 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -754,6 +754,7 @@ enum scx_rq_flags {
 	SCX_RQ_BAL_PENDING	= 1 << 2, /* balance hasn't run yet */
 	SCX_RQ_BAL_KEEP		= 1 << 3, /* balance decided to keep current */
 	SCX_RQ_BYPASSING	= 1 << 4,
+	SCX_RQ_CLK_VALID	= 1 << 5, /* RQ clock is fresh and valid */
 
 	SCX_RQ_IN_WAKEUP	= 1 << 16,
 	SCX_RQ_IN_BALANCE	= 1 << 17,
@@ -766,8 +767,9 @@ struct scx_rq {
 	unsigned long		ops_qseq;
 	u64			extra_enq_flags;	/* see move_task_to_local_dsq() */
 	u32			nr_running;
-	u32			flags;
 	u32			cpuperf_target;		/* [0, SCHED_CAPACITY_SCALE] */
+	u64			clock;			/* cached per-rq clock -- see scx_bpf_clock_get_ns() */
+	u32			flags;
 	bool			cpu_released;
 	cpumask_var_t		cpus_to_kick;
 	cpumask_var_t		cpus_to_kick_if_idle;
@@ -1717,6 +1719,37 @@ struct rq_flags {
 
 extern struct balance_callback balance_push_callback;
 
+#ifdef CONFIG_SCHED_CLASS_EXT
+extern const struct sched_class ext_sched_class;
+
+DECLARE_STATIC_KEY_FALSE(__scx_ops_enabled);	/* SCX BPF scheduler loaded */
+DECLARE_STATIC_KEY_FALSE(__scx_switched_all);	/* all fair class tasks on SCX */
+
+#define scx_enabled()		static_branch_unlikely(&__scx_ops_enabled)
+#define scx_switched_all()	static_branch_unlikely(&__scx_switched_all)
+
+static inline void scx_rq_clock_update(struct rq *rq, u64 clock)
+{
+	if (scx_enabled()) {
+		rq->scx.clock = clock;
+		rq->scx.flags |= SCX_RQ_CLK_VALID;
+	}
+}
+
+static inline void scx_rq_clock_stale(struct rq *rq)
+{
+	if (scx_enabled())
+		rq->scx.flags &= ~SCX_RQ_CLK_VALID;
+}
+
+#else /* !CONFIG_SCHED_CLASS_EXT */
+#define scx_enabled()		false
+#define scx_switched_all()	false
+
+static inline void scx_rq_clock_update(struct rq *rq, u64 clock) {}
+static inline void scx_rq_clock_stale(struct rq *rq) {}
+#endif /* !CONFIG_SCHED_CLASS_EXT */
+
 /*
  * Lockdep annotation that avoids accidental unlocks; it's like a
  * sticky/continuous lockdep_assert_held().
@@ -2505,19 +2538,6 @@ extern const struct sched_class rt_sched_class;
 extern const struct sched_class fair_sched_class;
 extern const struct sched_class idle_sched_class;
 
-#ifdef CONFIG_SCHED_CLASS_EXT
-extern const struct sched_class ext_sched_class;
-
-DECLARE_STATIC_KEY_FALSE(__scx_ops_enabled);	/* SCX BPF scheduler loaded */
-DECLARE_STATIC_KEY_FALSE(__scx_switched_all);	/* all fair class tasks on SCX */
-
-#define scx_enabled()		static_branch_unlikely(&__scx_ops_enabled)
-#define scx_switched_all()	static_branch_unlikely(&__scx_switched_all)
-#else /* !CONFIG_SCHED_CLASS_EXT */
-#define scx_enabled()		false
-#define scx_switched_all()	false
-#endif /* !CONFIG_SCHED_CLASS_EXT */
-
 /*
  * Iterate only active classes. SCX can take over all fair tasks or be
  * completely disabled. If the former, skip fair. If the latter, skip SCX.
-- 
2.47.1