Re: [PATCH v2] sched: Account cgroup CPU time to the execution context

[Tejun Heo]

On Fri, Sep 04, 2026 at 11:47:07AM +0800, Hui Su wrote:
> Proxy execution separates the scheduling context from the execution
> context. Commit aa4f74dfd42b ("sched: Fix runtime accounting w/ split
> exec & sched contexts") made per-task and thread-group runtime
> accounting follow the task that actually executes, while cgroup CPU
> usage is charged to the donor.
> 
> When the donor and execution task belong to different cgroups, this
> makes a task's execution time count against a different cgroup from the
> one the task belongs to.
> 
> Cgroup CPU usage should follow the execution context, matching the
> per-task, thread-group, and cgroup user/system accounting. Keep
> scheduling state associated with the donor, but charge cgroup CPU
> usage to rq->curr.
> 
> A reproducer with the donor and execution task in separate cgroups
> showed the execution task accumulating runtime while cgroup CPU usage
> was charged to the donor's cgroup. With this change, the execution
> task's cgroup accumulates the CPU usage instead. The same behavior was
> verified with an RT donor and with legacy cpuacct accounting.
> 
> Fixes: aa4f74dfd42b ("sched: Fix runtime accounting w/ split exec & sched contexts")
> Suggested-by: Tejun Heo <tj@xxxxxxxxxx>
> Signed-off-by: Hui Su <sh_def@xxxxxxx>

Provided John is okay with going this way:

Acked-by: Tejun Heo <tj@xxxxxxxxxx>

> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 8dff37059faf..6fcf67d741e8 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1404,7 +1404,6 @@ static s64 update_se(struct rq *rq, struct sched_entity *se)
>  
>  	se->exec_start = now;
>  	if (entity_is_task(se)) {
> -		struct task_struct *donor = task_of(se);
>  		struct task_struct *running = rq->curr;
>  		/*
>  		 * If se is a task, we account the time against the running
> @@ -1417,8 +1416,7 @@ static s64 update_se(struct rq *rq, struct sched_entity *se)
>  		account_group_exec_runtime(running, delta_exec);
>  		account_mm_sched(rq, running, delta_exec);
>  
> -		/* cgroup time is always accounted against the donor */
> -		cgroup_account_cputime(donor, delta_exec);
> +		cgroup_account_cputime(running, delta_exec);

The diff looks so much better.

Thanks.

-- 
tejun