Re: [PATCH v2 10/10] sched/eevdf: Move to a single runqueue

[Zhang Qiao]

Hi Peter,

在 2026/5/11 19:31, Peter Zijlstra 写道:

> @@ -13729,14 +13616,20 @@ static inline void task_tick_core(struct
>   */
>  static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
>  {
> -	struct cfs_rq *cfs_rq;
>  	struct sched_entity *se = &curr->se;
> +	unsigned long weight = NICE_0_LOAD;
> +	struct cfs_rq *cfs_rq;
>  
>  	for_each_sched_entity(se) {
>  		cfs_rq = cfs_rq_of(se);
>  		entity_tick(cfs_rq, se, queued);
> +
> +		weight = __calc_prop_weight(cfs_rq, se, weight);

Testing sched/flat branch on AMD EPYC 9654 (384 CPUs, 8 NUMA nodes)
with a 2-level cgroup hierarchy and cfs_bandwidth quota enabled,
hackbench triggers a divide-by-zero oops:

  [  142.308571] divide error: 0000 [#1] SMP NOPTI
  [  142.308582] RIP: 0010:task_tick_fair+0x19e/0x410
  [  142.308601] Call Trace:
  [  142.308604]  <IRQ>
  [  142.308607]  scheduler_tick+0x6a/0x110
  [  142.308609]  update_process_times+0x6b/0x90
  [  142.308611]  tick_sched_handle+0x2a/0x70
  [  142.308613]  tick_sched_timer+0x57/0xb0

faddr2line confirms:

  task_tick_fair+0x19e/0x410:
  __calc_prop_weight at kernel/sched/fair.c:4085
  (inlined by) task_tick_fair at kernel/sched/fair.c:13576

===========================================================
Reproduction
===========================================================

Kernel: sched/flat branch (54d493980e00 and later)
Hardware: AMD EPYC 9654, 2S 384 logical CPUs

  # 2-level cgroup, quota = 50% of one period
  cgcreate -g cpu:/bw/l1/l2
  cgset -r cpu.cfs_quota_us=50000  /bw/l1/l2
  cgset -r cpu.cfs_period_us=100000 /bw/l1/l2

  # high task count amplifies the throttle→tick race window
  cgexec -g cpu:/bw/l1/l2 hackbench -g 48 -l 1000 -s 512 -T

Typically crashes within 30 seconds on this machine.  A single-CPU
kernel or a very loose quota (e.g. 90%) is unlikely to trigger it
because the race window is narrow.

Thanks,
Zhang Qiao

>  	}
>  
> +	se = &curr->se;
> +	reweight_eevdf(cfs_rq, se, weight, se->on_rq);
> +
>  	if (queued)
>  		return;
>  
> @@ -13772,7 +13665,7 @@ prio_changed_fair(struct rq *rq, struct
>  	if (p->prio == oldprio)
>  		return;
>  
> -	if (rq->cfs.nr_queued == 1)
> +	if (rq->cfs.h_nr_queued == 1)
>  		return;
>  
>  	/*
> @@ -13901,29 +13794,40 @@ static void switched_to_fair(struct rq *
>  	}
>  }
>  

>  
> 
> 
> 
> 
> .
>