[PATCH v3 0/2] sched_ext: pass the initial cpu.idle state in scx_cgroup_init_args

[PATCH v3 0/2] sched_ext: pass the initial cpu.idle state in scx_cgroup_init_args

[Tao Cui]

From: Tao Cui <cuitao@kylinos.cn>

This carries the initial cpu.idle state of a cgroup through
ops.cgroup_init(), which was the only cpu controller knob whose
initial value never reached the BPF scheduler. Patch 1 is the fix;
patch 2 renames tg->scx.idle to tg->scx.sched_idle, suggested in
review, as a separate cleanup.

Changes since v2:

- rename the new field to sched_idle, as a bare "idle" reads as CPU
  idle state in sched_ext (Tejun)
- split the tg->scx.idle rename into 2/2 so 1/2 stays minimal for
  stable backport
- add the Fixes: tag (Andrea)
- regenerate on top of current linux-next, which also resolves the CI
  conflict reported against v2

v2: https://lore.kernel.org/r/20260824142817.568085-1-cui.tao@linux.dev
v1: https://lore.kernel.org/r/20260824133954.561956-1-cui.tao@linux.dev

Tao Cui (2):
  sched_ext: pass the initial cpu.idle state in scx_cgroup_init_args
  sched_ext: rename tg->scx.idle to tg->scx.sched_idle

 include/linux/sched/ext.h   | 2 +-
 kernel/sched/ext/ext.c      | 8 +++++---
 kernel/sched/ext/internal.h | 3 +++
 kernel/sched/ext/sub.c      | 2 ++
 4 files changed, 11 insertions(+), 4 deletions(-)

-- 
2.43.0

[PATCH v3 1/2] sched_ext: pass the initial cpu.idle state in scx_cgroup_init_args

[Tao Cui]

From: Tao Cui <cuitao@kylinos.cn>

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 sched_idle state to scx_cgroup_init_args and fill it in all
four places that build the args: scx_tg_online() for cgroups onlined
under the scheduler, scx_cgroup_init() for cgroups that already exist
when the scheduler is loaded, and the sub-scheduler handover paths
scx_cgroup_claim_subtree() and scx_cgroup_return_subtree().

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

Fixes: 347ed2d566da ("sched/ext: Implement cgroup_set_idle() callback")
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
---
v2 -> v3: Rename the new field to sched_idle, as a bare "idle" reads
as CPU idle state in sched_ext, per Tejun. Add the Fixes: tag
suggested by Andrea. Regenerated on top of current linux-next, which
also resolves the CI conflict reported for v2. The tg->scx.idle
rename now lives in 2/2.

v2: https://lore.kernel.org/r/20260824142817.568085-1-cui.tao@linux.dev

 kernel/sched/ext/ext.c      | 4 +++-
 kernel/sched/ext/internal.h | 3 +++
 kernel/sched/ext/sub.c      | 2 ++
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
index c539d15cda63..82cf8f57e15c 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,
+				  .sched_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,
+				.sched_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..c6987a3a073b 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 SCHED_IDLE via cpu.idle */
+	bool			sched_idle;
 };
 
 enum scx_cpu_preempt_reason {
diff --git a/kernel/sched/ext/sub.c b/kernel/sched/ext/sub.c
index 0554448835bd..385302d19914 100644
--- a/kernel/sched/ext/sub.c
+++ b/kernel/sched/ext/sub.c
@@ -1361,6 +1361,7 @@ static s32 scx_cgroup_claim_subtree(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,
+			.sched_idle = tg->scx.idle,
 		};
 
 		if (tg->scx.sched != parent ||
@@ -1464,6 +1465,7 @@ static void scx_cgroup_return_subtree(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,
+			.sched_idle = tg->scx.idle,
 		};
 
 		/* the first pass must have transferred everything */
-- 
2.43.0

[PATCH v3 2/2] sched_ext: rename tg->scx.idle to tg->scx.sched_idle

[Tao Cui]

From: Tao Cui <cuitao@kylinos.cn>

A bare "idle" reads as CPU idle state in sched_ext (ops.update_idle(),
idle cpumasks, scx_bpf_pick_idle_cpu()). cpu.idle is the cgroup analog
of the SCHED_IDLE policy, so name the task_group field sched_idle to
match scx_cgroup_init_args.sched_idle.

Pure rename, no behavior change.

Signed-off-by: Tao Cui <cuitao@kylinos.cn>
---
 include/linux/sched/ext.h | 2 +-
 kernel/sched/ext/ext.c    | 8 ++++----
 kernel/sched/ext/sub.c    | 4 ++--
 3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/include/linux/sched/ext.h b/include/linux/sched/ext.h
index 582d7cd4a983..7b9cdb65deef 100644
--- a/include/linux/sched/ext.h
+++ b/include/linux/sched/ext.h
@@ -323,7 +323,7 @@ struct scx_task_group {
 	u64			bw_period_us;
 	u64			bw_quota_us;
 	u64			bw_burst_us;
-	bool			idle;
+	bool			sched_idle;
 #endif
 };
 
diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
index 82cf8f57e15c..4a9c38297093 100644
--- a/kernel/sched/ext/ext.c
+++ b/kernel/sched/ext/ext.c
@@ -4682,7 +4682,7 @@ void scx_tg_init(struct task_group *tg)
 	tg->scx.weight = CGROUP_WEIGHT_DFL;
 	tg->scx.bw_period_us = default_bw_period_us();
 	tg->scx.bw_quota_us = RUNTIME_INF;
-	tg->scx.idle = false;
+	tg->scx.sched_idle = false;
 }
 
 /**
@@ -4765,7 +4765,7 @@ int scx_tg_online(struct task_group *tg)
 				  .bw_period_us = tg->scx.bw_period_us,
 				  .bw_quota_us = tg->scx.bw_quota_us,
 				  .bw_burst_us = tg->scx.bw_burst_us,
-				  .sched_idle = tg->scx.idle };
+				  .sched_idle = tg->scx.sched_idle };
 
 			ret = SCX_CALL_OP_RET(sch, cgroup_init,
 					      NULL, tg->css.cgroup, &args);
@@ -4935,7 +4935,7 @@ void scx_group_set_idle(struct task_group *tg, bool idle)
 		SCX_CALL_OP(sch, cgroup_set_idle, NULL, tg_cgrp(tg), idle);
 
 	/* Update the task group's idle state */
-	tg->scx.idle = idle;
+	tg->scx.sched_idle = idle;
 
 	percpu_up_read(&scx_cgroup_ops_rwsem);
 }
@@ -5186,7 +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,
-				.sched_idle = tg->scx.idle,
+				.sched_idle = tg->scx.sched_idle,
 			};
 
 			ret = SCX_CALL_OP_RET(sch, cgroup_init, NULL, css->cgroup, &args);
diff --git a/kernel/sched/ext/sub.c b/kernel/sched/ext/sub.c
index 385302d19914..a17d84db93bd 100644
--- a/kernel/sched/ext/sub.c
+++ b/kernel/sched/ext/sub.c
@@ -1361,7 +1361,7 @@ static s32 scx_cgroup_claim_subtree(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,
-			.sched_idle = tg->scx.idle,
+			.sched_idle = tg->scx.sched_idle,
 		};
 
 		if (tg->scx.sched != parent ||
@@ -1465,7 +1465,7 @@ static void scx_cgroup_return_subtree(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,
-			.sched_idle = tg->scx.idle,
+			.sched_idle = tg->scx.sched_idle,
 		};
 
 		/* the first pass must have transferred everything */
-- 
2.43.0

Re: [PATCH v3 2/2] sched_ext: rename tg->scx.idle to tg->scx.sched_idle

[Tao Cui]

Hi,

在 2026/8/25 10:35, Tao Cui 写道:
> From: Tao Cui <cuitao@kylinos.cn>
> 
> A bare "idle" reads as CPU idle state in sched_ext (ops.update_idle(),
> idle cpumasks, scx_bpf_pick_idle_cpu()). cpu.idle is the cgroup analog
> of the SCHED_IDLE policy, so name the task_group field sched_idle to
> match scx_cgroup_init_args.sched_idle.
> 
> Pure rename, no behavior change.
> 

While testing this series, I noticed that scx_group_set_idle() delivers
ops.cgroup_set_idle() on every successful cpu.idle write, even rewrites
of the current value, although the kerneldoc says the callback is
invoked on transitions. scx_group_set_weight() and
scx_group_set_bandwidth() both skip unchanged values, so this seems
like an oversight.

The fix is a one-line guard, but it reads the field renamed here, so
I'll post it on top of this series once it lands.

Thanks,
Tao

> Signed-off-by: Tao Cui <cuitao@kylinos.cn>
> ---
>  include/linux/sched/ext.h | 2 +-
>  kernel/sched/ext/ext.c    | 8 ++++----
>  kernel/sched/ext/sub.c    | 4 ++--
>  3 files changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/sched/ext.h b/include/linux/sched/ext.h
> index 582d7cd4a983..7b9cdb65deef 100644
> --- a/include/linux/sched/ext.h
> +++ b/include/linux/sched/ext.h
> @@ -323,7 +323,7 @@ struct scx_task_group {
>  	u64			bw_period_us;
>  	u64			bw_quota_us;
>  	u64			bw_burst_us;
> -	bool			idle;
> +	bool			sched_idle;
>  #endif
>  };
>  
> diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
> index 82cf8f57e15c..4a9c38297093 100644
> --- a/kernel/sched/ext/ext.c
> +++ b/kernel/sched/ext/ext.c
> @@ -4682,7 +4682,7 @@ void scx_tg_init(struct task_group *tg)
>  	tg->scx.weight = CGROUP_WEIGHT_DFL;
>  	tg->scx.bw_period_us = default_bw_period_us();
>  	tg->scx.bw_quota_us = RUNTIME_INF;
> -	tg->scx.idle = false;
> +	tg->scx.sched_idle = false;
>  }
>  
>  /**
> @@ -4765,7 +4765,7 @@ int scx_tg_online(struct task_group *tg)
>  				  .bw_period_us = tg->scx.bw_period_us,
>  				  .bw_quota_us = tg->scx.bw_quota_us,
>  				  .bw_burst_us = tg->scx.bw_burst_us,
> -				  .sched_idle = tg->scx.idle };
> +				  .sched_idle = tg->scx.sched_idle };
>  
>  			ret = SCX_CALL_OP_RET(sch, cgroup_init,
>  					      NULL, tg->css.cgroup, &args);
> @@ -4935,7 +4935,7 @@ void scx_group_set_idle(struct task_group *tg, bool idle)
>  		SCX_CALL_OP(sch, cgroup_set_idle, NULL, tg_cgrp(tg), idle);
>  
>  	/* Update the task group's idle state */
> -	tg->scx.idle = idle;
> +	tg->scx.sched_idle = idle;
>  
>  	percpu_up_read(&scx_cgroup_ops_rwsem);
>  }
> @@ -5186,7 +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,
> -				.sched_idle = tg->scx.idle,
> +				.sched_idle = tg->scx.sched_idle,
>  			};
>  
>  			ret = SCX_CALL_OP_RET(sch, cgroup_init, NULL, css->cgroup, &args);
> diff --git a/kernel/sched/ext/sub.c b/kernel/sched/ext/sub.c
> index 385302d19914..a17d84db93bd 100644
> --- a/kernel/sched/ext/sub.c
> +++ b/kernel/sched/ext/sub.c
> @@ -1361,7 +1361,7 @@ static s32 scx_cgroup_claim_subtree(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,
> -			.sched_idle = tg->scx.idle,
> +			.sched_idle = tg->scx.sched_idle,
>  		};
>  
>  		if (tg->scx.sched != parent ||
> @@ -1465,7 +1465,7 @@ static void scx_cgroup_return_subtree(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,
> -			.sched_idle = tg->scx.idle,
> +			.sched_idle = tg->scx.sched_idle,
>  		};
>  
>  		/* the first pass must have transferred everything */

Re: [PATCH v3 0/2] sched_ext: pass the initial cpu.idle state in scx_cgroup_init_args

[Andrea Righi]

On Tue, Aug 25, 2026 at 10:35:55AM +0800, Tao Cui wrote:
> From: Tao Cui <cuitao@kylinos.cn>
> 
> This carries the initial cpu.idle state of a cgroup through
> ops.cgroup_init(), which was the only cpu controller knob whose
> initial value never reached the BPF scheduler. Patch 1 is the fix;
> patch 2 renames tg->scx.idle to tg->scx.sched_idle, suggested in
> review, as a separate cleanup.

This looks good to me.

Reviewed-by: Andrea Righi <arighi@nvidia.com>

Thanks,
-Andrea

> 
> Changes since v2:
> 
> - rename the new field to sched_idle, as a bare "idle" reads as CPU
>   idle state in sched_ext (Tejun)
> - split the tg->scx.idle rename into 2/2 so 1/2 stays minimal for
>   stable backport
> - add the Fixes: tag (Andrea)
> - regenerate on top of current linux-next, which also resolves the CI
>   conflict reported against v2
> 
> v2: https://lore.kernel.org/r/20260824142817.568085-1-cui.tao@linux.dev
> v1: https://lore.kernel.org/r/20260824133954.561956-1-cui.tao@linux.dev
> 
> Tao Cui (2):
>   sched_ext: pass the initial cpu.idle state in scx_cgroup_init_args
>   sched_ext: rename tg->scx.idle to tg->scx.sched_idle
> 
>  include/linux/sched/ext.h   | 2 +-
>  kernel/sched/ext/ext.c      | 8 +++++---
>  kernel/sched/ext/internal.h | 3 +++
>  kernel/sched/ext/sub.c      | 2 ++
>  4 files changed, 11 insertions(+), 4 deletions(-)
> 
> -- 
> 2.43.0
>