Re: [PATCH 0/2] sched/fair: Use cfs_rq->h_curr in the bandwidth paths

[Aaron Lu]

On Mon, Aug 31, 2026 at 06:11:39PM +0800, Wanwu Li wrote:
> Hi Peter, Ingo,
> 
> Since commit 85570f10a4c6 ("sched/eevdf: Move to a single runqueue")
> the per-level "is something running at this level" information moved
> from cfs_rq->curr to cfs_rq->h_curr; cfs_rq->curr is now only
> maintained on the root cfs_rq. The cgroup hierarchy is kept for load
> tracking and bandwidth accounting, which makes the bandwidth paths the
> only code that still runs per-level and consults a per-level current.
> Two locations were not updated in this conversion:
> 
>   1/2: throttle_cfs_rq() reads cfs_rq->curr to decide whether the
>        throttled level has a running entity. For intermediate cfs_rqs
>        the check is always false, so quota exhaustion never requests a
>        full sched_cfs_bandwidth_slice() and never arms the deferred
>        throttle task_work via task_throttle_setup_work(); a running
>        task can out-run its group's quota until the next pick armed
>        the work instead.
> 
>   2/2: distribute_cfs_runtime() gates its clock refresh and runtime
>        accounting on cfs_rq->curr, which never fires for cgroup
>        cfs_rqs. Since commit 28ad5427682b ("sched/fair: Call
>        update_curr() before unthrottling the hierarchy")
>        unthrottle_cfs_rq() catches up unconditionally, so this is not
>        a correctness hole today, but the refresh the check was written
>        for is gone.

For this series:
Reviewed-by: Aaron Lu <ziqianlu@xxxxxxxxxxxxx>

I also run a test where a nop is affined to a single cpu and I can see
that nop task can use more than its quota from time to time; with this
series applied, this no longer happens, so:
Tested-by: Aaron Lu <ziqianlu@xxxxxxxxxxxxx>