Re: [PATCH v3 1/2] sched/numa: Drive NUMA task tick from execution context

[Tim Chen]

On Fri, 2026-09-04 at 16:52 +0800, Hui Su wrote:
> Proxy execution separates the scheduling context in rq->donor from the
> execution context in rq->curr. sched_tick() invokes task_tick() for the
> donor's scheduling class.
> 
> task_tick_numa() operates on state associated with the task actually
> executing, including its mm and NUMA work state. With proxy execution,
> rq->donor provides the scheduling context while rq->curr identifies the
> execution context.
> 
> Task-level execution runtime is likewise accounted to rq->curr, and
> task_tick_numa() uses that runtime to drive periodic NUMA scanning.
> Keeping task_tick_numa() under task_tick_fair() also means that it is not
> invoked when a fair task executes on behalf of an RT or deadline donor.
> 
> Move NUMA tick handling into a scheduler helper for the execution
> context, and invoke it from both sched_tick() and sched_tick_remote().
> 
> Fixes: 7de9d4f94638 ("sched: Start blocked_on chain processing in find_proxy_task()")
> Suggested-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
> Suggested-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
> Signed-off-by: Hui Su <sh_def@xxxxxxx>
> ---
>  kernel/sched/core.c  | 14 ++++++++++++++
>  kernel/sched/fair.c  |  7 ++-----
>  kernel/sched/sched.h |  1 +
>  3 files changed, 17 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index f78275192036..4db55e4ace9e 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -5762,6 +5762,17 @@ static int __init setup_resched_latency_warn_ms(char *str)
>  }
>  __setup("resched_latency_warn_ms=", setup_resched_latency_warn_ms);
>  
> +static void sched_tick_exec_ctx(struct rq *rq)

Just a minor nit.  We could consider putting sched_tick_exec_ctx()
in fair.c and export it instead.
That allows task_tick_numa() and task_tick_cache() declaration to
remain static.

No big deal either way.

Otherwise the two patches in the series look good to me.

Reviewed-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>

Tim

> +{
> +	struct task_struct *curr = rq->curr;
> +
> +	if (curr->sched_class != &fair_sched_class)
> +		return;
> +
> +	if (static_branch_unlikely(&sched_numa_balancing))
> +		task_tick_numa(rq, curr);
> +}
> +
>  /*
>   * This function gets called by the timer code, with HZ frequency.
>   * We call it with interrupts disabled.
> @@ -5794,6 +5805,8 @@ void sched_tick(void)
>  		resched_curr(rq);
>  
>  	donor->sched_class->task_tick(rq, donor, 0);
> +	sched_tick_exec_ctx(rq);
> +
>  	if (sched_feat(LATENCY_WARN))
>  		resched_latency = cpu_resched_latency(rq);
>  	calc_global_load_tick(rq);
> @@ -5890,6 +5903,7 @@ static void sched_tick_remote(struct work_struct *work)
>  				WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 30);
>  			}
>  			curr->sched_class->task_tick(rq, curr, 0);
> +			sched_tick_exec_ctx(rq);
>  
>  			calc_load_nohz_remote(rq);
>  		}
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 8dff37059faf..55f0460e4ae3 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4425,7 +4425,7 @@ void init_numa_balancing(u64 clone_flags, struct task_struct *p)
>  /*
>   * Drive the periodic memory faults..
>   */
> -static void task_tick_numa(struct rq *rq, struct task_struct *curr)
> +void task_tick_numa(struct rq *rq, struct task_struct *curr)
>  {
>  	struct callback_head *work = &curr->numa_work;
>  	u64 period, now;
> @@ -4491,7 +4491,7 @@ static void update_scan_period(struct task_struct *p, int new_cpu)
>  
>  #else /* !CONFIG_NUMA_BALANCING: */
>  
> -static void task_tick_numa(struct rq *rq, struct task_struct *curr)
> +void task_tick_numa(struct rq *rq, struct task_struct *curr)
>  {
>  }
>  
> @@ -15042,9 +15042,6 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
>  	if (queued)
>  		return;
>  
> -	if (static_branch_unlikely(&sched_numa_balancing))
> -		task_tick_numa(rq, curr);
> -
>  	task_tick_cache(rq, curr);
>  
>  	update_misfit_status(curr, rq);
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index e656c7059bf8..4d619f272b15 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -4152,6 +4152,7 @@ extern void sched_cache_active_set(void);
>  void sched_domains_free_llc_id(int cpu);
>  
>  extern void init_sched_mm(struct task_struct *p);
> +void task_tick_numa(struct rq *rq, struct task_struct *p);
>  
>  extern u64 avg_vruntime(struct cfs_rq *cfs_rq);
>  extern int entity_eligible(struct cfs_rq *cfs_rq, struct sched_entity *se);
>