[PATCH 14/15] sched_ext: Simplify task state handling

[Tejun Heo]

Task states (NONE, INIT, READY, ENABLED) were defined in a separate enum with
unshifted values and then shifted when stored in scx_entity.flags. Simplify by
defining them as pre-shifted values directly in scx_ent_flags and removing the
separate scx_task_state enum. This removes the need for shifting when
reading/writing state values.

scx_get_task_state() now returns the masked flags value directly.
scx_set_task_state() accepts the pre-shifted state value. scx_dump_task()
shifts down for display to maintain readable output.

No functional changes.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
 include/linux/sched/ext.h | 28 ++++++++++++++++------------
 kernel/sched/ext.c        | 19 +++++++++----------
 2 files changed, 25 insertions(+), 22 deletions(-)

diff --git a/include/linux/sched/ext.h b/include/linux/sched/ext.h
index e77504faa0bc..e822b374b17f 100644
--- a/include/linux/sched/ext.h
+++ b/include/linux/sched/ext.h
@@ -93,7 +93,7 @@ struct scx_dispatch_q {
 	struct rcu_head		rcu;
 };
 
-/* scx_entity.flags */
+/* sched_ext_entity.flags */
 enum scx_ent_flags {
 	SCX_TASK_QUEUED		= 1 << 0, /* on ext runqueue */
 	SCX_TASK_IN_CUSTODY	= 1 << 1, /* in custody, needs ops.dequeue() when leaving */
@@ -101,21 +101,25 @@ enum scx_ent_flags {
 	SCX_TASK_DEQD_FOR_SLEEP	= 1 << 3, /* last dequeue was for SLEEP */
 	SCX_TASK_SUB_INIT	= 1 << 4, /* task being initialized for a sub sched */
 
-	SCX_TASK_STATE_SHIFT	= 8,	  /* bit 8 and 9 are used to carry scx_task_state */
+	/*
+	 * Bits 8 and 9 are used to carry task state:
+	 *
+	 * NONE		ops.init_task() not called yet
+	 * INIT		ops.init_task() succeeded, but task can be cancelled
+	 * READY	fully initialized, but not in sched_ext
+	 * ENABLED	fully initialized and in sched_ext
+	 */
+	SCX_TASK_STATE_SHIFT	= 8,	  /* bits 8 and 9 are used to carry task state */
 	SCX_TASK_STATE_BITS	= 2,
 	SCX_TASK_STATE_MASK	= ((1 << SCX_TASK_STATE_BITS) - 1) << SCX_TASK_STATE_SHIFT,
 
-	SCX_TASK_CURSOR		= 1 << 31, /* iteration cursor, not a task */
-};
-
-/* scx_entity.flags & SCX_TASK_STATE_MASK */
-enum scx_task_state {
-	SCX_TASK_NONE,		/* ops.init_task() not called yet */
-	SCX_TASK_INIT,		/* ops.init_task() succeeded, but task can be cancelled */
-	SCX_TASK_READY,		/* fully initialized, but not in sched_ext */
-	SCX_TASK_ENABLED,	/* fully initialized and in sched_ext */
+	SCX_TASK_NONE		= 0 << SCX_TASK_STATE_SHIFT,
+	SCX_TASK_INIT		= 1 << SCX_TASK_STATE_SHIFT,
+	SCX_TASK_READY		= 2 << SCX_TASK_STATE_SHIFT,
+	SCX_TASK_ENABLED	= 3 << SCX_TASK_STATE_SHIFT,
 
-	SCX_TASK_NR_STATES,
+	/* iteration cursor, not a task */
+	SCX_TASK_CURSOR		= 1 << 31,
 };
 
 /* scx_entity.dsq_flags */
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 8e7dffe4094c..df659e51bd8a 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -3312,18 +3312,16 @@ static struct cgroup *tg_cgrp(struct task_group *tg)
 
 #endif	/* CONFIG_EXT_GROUP_SCHED */
 
-static enum scx_task_state scx_get_task_state(const struct task_struct *p)
+static u32 scx_get_task_state(const struct task_struct *p)
 {
-	return (p->scx.flags & SCX_TASK_STATE_MASK) >> SCX_TASK_STATE_SHIFT;
+	return p->scx.flags & SCX_TASK_STATE_MASK;
 }
 
-static void scx_set_task_state(struct task_struct *p, enum scx_task_state state)
+static void scx_set_task_state(struct task_struct *p, u32 state)
 {
-	enum scx_task_state prev_state = scx_get_task_state(p);
+	u32 prev_state = scx_get_task_state(p);
 	bool warn = false;
 
-	BUILD_BUG_ON(SCX_TASK_NR_STATES > (1 << SCX_TASK_STATE_BITS));
-
 	switch (state) {
 	case SCX_TASK_NONE:
 		break;
@@ -3341,11 +3339,11 @@ static void scx_set_task_state(struct task_struct *p, enum scx_task_state state)
 		return;
 	}
 
-	WARN_ONCE(warn, "sched_ext: Invalid task state transition %d -> %d for %s[%d]",
+	WARN_ONCE(warn, "sched_ext: Invalid task state transition 0x%x -> 0x%x for %s[%d]",
 		  prev_state, state, p->comm, p->pid);
 
 	p->scx.flags &= ~SCX_TASK_STATE_MASK;
-	p->scx.flags |= state << SCX_TASK_STATE_SHIFT;
+	p->scx.flags |= state;
 }
 
 static int __scx_init_task(struct scx_sched *sch, struct task_struct *p, bool fork)
@@ -5795,7 +5793,8 @@ static void scx_dump_task(struct scx_sched *sch,
 		  own_marker, sch_id_buf,
 		  jiffies_delta_msecs(p->scx.runnable_at, dctx->at_jiffies));
 	dump_line(s, "      scx_state/flags=%u/0x%x dsq_flags=0x%x ops_state/qseq=%lu/%lu",
-		  scx_get_task_state(p), p->scx.flags & ~SCX_TASK_STATE_MASK,
+		  scx_get_task_state(p) >> SCX_TASK_STATE_SHIFT,
+		  p->scx.flags & ~SCX_TASK_STATE_MASK,
 		  p->scx.dsq_flags, ops_state & SCX_OPSS_STATE_MASK,
 		  ops_state >> SCX_OPSS_QSEQ_SHIFT);
 	dump_line(s, "      sticky/holding_cpu=%d/%d dsq_id=%s",
@@ -6556,7 +6555,7 @@ static struct scx_sched *find_parent_sched(struct cgroup *cgrp)
 
 static bool assert_task_ready_or_enabled(struct task_struct *p)
 {
-	enum scx_task_state state = scx_get_task_state(p);
+	u32 state = scx_get_task_state(p);
 
 	switch (state) {
 	case SCX_TASK_READY:
-- 
2.53.0