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

[Tao Cui]

Hello, Andrea

在 2026/8/24 22:11, Andrea Righi 写道:
> Hi Tao,
> 
> On Mon, Aug 24, 2026 at 09:39:54PM +0800, Tao Cui wrote:
>> From: Tao Cui <cuitao@xxxxxxxxxx>
>>
>> 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 <cuitao@xxxxxxxxxx>
>> ---
>>  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;
>>  };
> 
> It looks like there are two more places in kernel/sched/ext/sub.c,
> scx_cgroup_claim_subtree() and scx_cgroup_return_subtree(), they should also
> initialize idle. Otherwise the field defaults to false and an idle cgroup would
> be presented as non-idle when it's handed to a sub-scheduler.
> 

Right, I missed those two. v2 fills .idle in all four places that
build scx_cgroup_init_args, including both sub-scheduler handover
paths in sub.c. The main paths are verified in a VM; the sub.c ones
are compile-tested only.

Thanks,
Tao> Thanks,
> -Andrea