[PATCH] sched_ext: pass the initial cpu.idle state in scx_cgroup_init_args

From: Tao Cui <[email protected]>

scx_cgroup_init_args carries the initial weight and bandwidth control
parameters of a cgroup to ops.cgroup_init(), but not its cpu.idle
state. A cgroup that was already configured idle before the scheduler
was loaded (or before it was onlined under it) is presented as
non-idle, and the BPF scheduler only learns about it if cpu.idle is
written again later.

Add the idle state to scx_cgroup_init_args and fill it in both places
that build the args -- scx_tg_online() for cgroups created under the
scheduler and scx_cgroup_init() for cgroups that already exist when
the scheduler is loaded.

Verified in a VM with a probe scheduler printing the init args: a
cgroup configured cpu.idle=1 before loading shows idle=1 in
ops.cgroup_init(), the default shows 0, and later cpu.idle writes
still come through ops.cgroup_set_idle().

Signed-off-by: Tao Cui <[email protected]>
---
 kernel/sched/ext/ext.c      | 4 +++-
 kernel/sched/ext/internal.h | 3 +++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
index b646711a45fe..a7218314dcfb 100644
--- a/kernel/sched/ext/ext.c
+++ b/kernel/sched/ext/ext.c
@@ -4764,7 +4764,8 @@ int scx_tg_online(struct task_group *tg)
 				{ .weight = tg->scx.weight,
 				  .bw_period_us = tg->scx.bw_period_us,
 				  .bw_quota_us = tg->scx.bw_quota_us,
-				  .bw_burst_us = tg->scx.bw_burst_us };
+				  .bw_burst_us = tg->scx.bw_burst_us,
+				  .idle = tg->scx.idle };
 
 			ret = SCX_CALL_OP_RET(sch, cgroup_init,
 					      NULL, tg->css.cgroup, &args);
@@ -5185,6 +5186,7 @@ static int scx_cgroup_init(struct scx_sched *sch)
 				.bw_period_us = tg->scx.bw_period_us,
 				.bw_quota_us = tg->scx.bw_quota_us,
 				.bw_burst_us = tg->scx.bw_burst_us,
+				.idle = tg->scx.idle,
 			};
 
 			ret = SCX_CALL_OP_RET(sch, cgroup_init, NULL, css->cgroup, &args);
diff --git a/kernel/sched/ext/internal.h b/kernel/sched/ext/internal.h
index 53e136a47924..aa149a9c29f7 100644
--- a/kernel/sched/ext/internal.h
+++ b/kernel/sched/ext/internal.h
@@ -259,6 +259,9 @@ struct scx_cgroup_init_args {
 	u64			bw_period_us;
 	u64			bw_quota_us;
 	u64			bw_burst_us;
+
+	/* whether the cgroup is configured idle via cpu.idle */
+	bool			idle;
 };
 
 enum scx_cpu_preempt_reason {
-- 
2.43.0