[PATCH] sched/ext: Implement cgroup_set_idle() callback

[PATCH] sched/ext: Implement cgroup_set_idle() callback

[zhidao su]

From: zhidao su <suzhidao@xiaomi.com>

Implement the missing cgroup_set_idle() callback that was marked as a
TODO. This allows BPF schedulers to be notified when a cgroup's idle
state changes, enabling them to adjust their scheduling behavior
accordingly.

The implementation follows the same pattern as other cgroup callbacks
like cgroup_set_weight() and cgroup_set_bandwidth(). It checks if the
BPF scheduler has implemented the callback and invokes it with the
appropriate parameters.

Fixes a spelling error in the cgroup_set_bandwidth() documentation.

Signed-off-by: zhidao su <suzhidao@xiaomi.com>
---
 kernel/sched/ext.c | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 088ceff38c8a..72bf2ad382fb 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -688,12 +688,23 @@ struct sched_ext_ops {
 	 * 2_500_000. @cgrp is entitled to 2.5 CPUs. @burst_us can be
 	 * interpreted in the same fashion and specifies how much @cgrp can
 	 * burst temporarily. The specific control mechanism and thus the
-	 * interpretation of @period_us and burstiness is upto to the BPF
+	 * interpretation of @period_us and burstiness is up to the BPF
 	 * scheduler.
 	 */
 	void (*cgroup_set_bandwidth)(struct cgroup *cgrp,
 				     u64 period_us, u64 quota_us, u64 burst_us);
 
+	/**
+	 * @cgroup_set_idle: A cgroup's idle state is being changed
+	 * @cgrp: cgroup whose idle state is being updated
+	 * @idle: whether the cgroup is entering or exiting idle state
+	 *
+	 * Update @cgrp's idle state to @idle. This callback is invoked when
+	 * a cgroup transitions between idle and non-idle states, allowing the
+	 * BPF scheduler to adjust its behavior accordingly.
+	 */
+	void (*cgroup_set_idle)(struct cgroup *cgrp, bool idle);
+
 #endif	/* CONFIG_EXT_GROUP_SCHED */
 
 	/*
@@ -4258,7 +4269,15 @@ void scx_group_set_weight(struct task_group *tg, unsigned long weight)
 
 void scx_group_set_idle(struct task_group *tg, bool idle)
 {
-	/* TODO: Implement ops->cgroup_set_idle() */
+	struct scx_sched *sch = scx_root;
+
+	percpu_down_read(&scx_cgroup_rwsem);
+
+	if (scx_cgroup_enabled && SCX_HAS_OP(sch, cgroup_set_idle))
+		SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cgroup_set_idle, NULL,
+			    tg_cgrp(tg), idle);
+
+	percpu_up_read(&scx_cgroup_rwsem);
 }
 
 void scx_group_set_bandwidth(struct task_group *tg,
@@ -6004,6 +6023,7 @@ static void sched_ext_ops__cgroup_move(struct task_struct *p, struct cgroup *fro
 static void sched_ext_ops__cgroup_cancel_move(struct task_struct *p, struct cgroup *from, struct cgroup *to) {}
 static void sched_ext_ops__cgroup_set_weight(struct cgroup *cgrp, u32 weight) {}
 static void sched_ext_ops__cgroup_set_bandwidth(struct cgroup *cgrp, u64 period_us, u64 quota_us, u64 burst_us) {}
+static void sched_ext_ops__cgroup_set_idle(struct cgroup *cgrp, bool idle) {}
 #endif
 static void sched_ext_ops__cpu_online(s32 cpu) {}
 static void sched_ext_ops__cpu_offline(s32 cpu) {}
@@ -6042,6 +6062,7 @@ static struct sched_ext_ops __bpf_ops_sched_ext_ops = {
 	.cgroup_cancel_move	= sched_ext_ops__cgroup_cancel_move,
 	.cgroup_set_weight	= sched_ext_ops__cgroup_set_weight,
 	.cgroup_set_bandwidth	= sched_ext_ops__cgroup_set_bandwidth,
+	.cgroup_set_idle	= sched_ext_ops__cgroup_set_idle,
 #endif
 	.cpu_online		= sched_ext_ops__cpu_online,
 	.cpu_offline		= sched_ext_ops__cpu_offline,
-- 
2.43.0

Re: [PATCH] sched/ext: Implement cgroup_set_idle() callback

[Tejun Heo]

Hello,

On Tue, Sep 30, 2025 at 02:10:45PM +0800, zhidao su wrote:
> From: zhidao su <suzhidao@xiaomi.com>
> 
> Implement the missing cgroup_set_idle() callback that was marked as a
> TODO. This allows BPF schedulers to be notified when a cgroup's idle
> state changes, enabling them to adjust their scheduling behavior
> accordingly.
> 
> The implementation follows the same pattern as other cgroup callbacks
> like cgroup_set_weight() and cgroup_set_bandwidth(). It checks if the
> BPF scheduler has implemented the callback and invokes it with the
> appropriate parameters.

Can you please add tg->scx.idle which tracks the current state?

Thanks.

-- 
tejun

Re: [PATCH v2] sched/ext: Add tg->scx.idle which tracks the current state

[zhidao su]

v2: Add tg->scx.idle which tracks the current state  

FYI, thanks

[PATCH] sched/ext: Add tg->scx.idle which tracks the current state

[zhidao su]

Add an idle field to the scx_task_group structure to track the current
idle state of a task group. This field is initialized to false in
scx_tg_init() and updated in scx_group_set_idle() when the idle state
changes.

This allows BPF schedulers to check the current idle state of a task
group directly from the scx_task_group structure.

v2: Add tg->scx.idle which tracks the current state
Signed-off-by: zhidao su <soolaugust@gmail.com>
---
 include/linux/sched/ext.h | 1 +
 kernel/sched/ext.c        | 4 ++++
 2 files changed, 5 insertions(+)

diff --git a/include/linux/sched/ext.h b/include/linux/sched/ext.h
index 7047101dbf58..b65e9abafcb6 100644
--- a/include/linux/sched/ext.h
+++ b/include/linux/sched/ext.h
@@ -224,6 +224,7 @@ struct scx_task_group {
 	u64			bw_period_us;
 	u64			bw_quota_us;
 	u64			bw_burst_us;
+	bool			idle;
 #endif
 };
 
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 72bf2ad382fb..a2bbcc34e5d5 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -4103,6 +4103,7 @@ 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;
 }
 
 int scx_tg_online(struct task_group *tg)
@@ -4273,6 +4274,9 @@ void scx_group_set_idle(struct task_group *tg, bool idle)
 
 	percpu_down_read(&scx_cgroup_rwsem);
 
+	/* Update the task group's idle state */
+	tg->scx.idle = idle;
+
 	if (scx_cgroup_enabled && SCX_HAS_OP(sch, cgroup_set_idle))
 		SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cgroup_set_idle, NULL,
 			    tg_cgrp(tg), idle);
-- 
2.43.0

Re: [PATCH] sched/ext: Add tg->scx.idle which tracks the current state

[Tejun Heo]

On Wed, Oct 08, 2025 at 10:09:39AM +0800, zhidao su wrote:
> Add an idle field to the scx_task_group structure to track the current
> idle state of a task group. This field is initialized to false in
> scx_tg_init() and updated in scx_group_set_idle() when the idle state
> changes.
> 
> This allows BPF schedulers to check the current idle state of a task
> group directly from the scx_task_group structure.
> 
> v2: Add tg->scx.idle which tracks the current state

Hmm... maybe a blank line here? I don't know whether there actually is an
established convention but I don't think we usually put version delta
descriptions in the tag section.

> Signed-off-by: zhidao su <soolaugust@gmail.com>
...
> @@ -4273,6 +4274,9 @@ void scx_group_set_idle(struct task_group *tg, bool idle)
>  
>  	percpu_down_read(&scx_cgroup_rwsem);
>  
> +	/* Update the task group's idle state */
> +	tg->scx.idle = idle;
> +
>  	if (scx_cgroup_enabled && SCX_HAS_OP(sch, cgroup_set_idle))
>  		SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cgroup_set_idle, NULL,
>  			    tg_cgrp(tg), idle);

This can be either way but scx_group_set_weight() sets the weight after
calling the ops.cgroup_set_weight() is called, so let's match that.

Thanks.

-- 
tejun