linux-kernel - Re: [PATCH sched_ext/for-6.16] sched_ext: Remove cpu.weight / cpu.idle unimplemented warnings

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Message-ID: <Z_TXIe2fVpAt-CAg@gpd3>
Date: Tue, 8 Apr 2025 09:58:25 +0200
From: Andrea Righi <arighi@...dia.com>
To: Tejun Heo <tj@...nel.org>
Cc: David Vernet <void@...ifault.com>, Changwoo Min <changwoo@...lia.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH sched_ext/for-6.16] sched_ext: Remove cpu.weight /
 cpu.idle unimplemented warnings

Hi Tejun,

On Mon, Apr 07, 2025 at 01:20:04PM -1000, Tejun Heo wrote:
> sched_ext generates warnings when cpu.weight / cpu.idle are set to
> non-default values if the BPF scheduler doesn't implement weight support.
> These warnings don't provide much value while adding constant annoyance. A
> BPF scheduler may not implement any particular behavior and there's nothing
> particularly special about missing cgroup weight support. Drop the warnings.

Thanks for dropping these warnings. :)

Acked-by: Andrea Righi <arighi@...dia.com>

Should we also deprecate SCX_OPS_HAS_CGROUP_WEIGHT (not necessarily in this
patch)? It's basically unused at this point.

Thanks,
-Andrea

> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> ---
>  kernel/sched/ext.c |   40 +---------------------------------------
>  1 file changed, 1 insertion(+), 39 deletions(-)
> 
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -3896,34 +3896,6 @@ bool scx_can_stop_tick(struct rq *rq)
>  
>  DEFINE_STATIC_PERCPU_RWSEM(scx_cgroup_rwsem);
>  static bool scx_cgroup_enabled;
> -static bool cgroup_warned_missing_weight;
> -static bool cgroup_warned_missing_idle;
> -
> -static void scx_cgroup_warn_missing_weight(struct task_group *tg)
> -{
> -	if (scx_enable_state() == SCX_DISABLED || cgroup_warned_missing_weight)
> -		return;
> -
> -	if ((scx_ops.flags & SCX_OPS_HAS_CGROUP_WEIGHT) || !tg->css.parent)
> -		return;
> -
> -	pr_warn("sched_ext: \"%s\" does not implement cgroup cpu.weight\n",
> -		scx_ops.name);
> -	cgroup_warned_missing_weight = true;
> -}
> -
> -static void scx_cgroup_warn_missing_idle(struct task_group *tg)
> -{
> -	if (!scx_cgroup_enabled || cgroup_warned_missing_idle)
> -		return;
> -
> -	if (!tg->idle)
> -		return;
> -
> -	pr_warn("sched_ext: \"%s\" does not implement cgroup cpu.idle\n",
> -		scx_ops.name);
> -	cgroup_warned_missing_idle = true;
> -}
>  
>  int scx_tg_online(struct task_group *tg)
>  {
> @@ -3933,8 +3905,6 @@ int scx_tg_online(struct task_group *tg)
>  
>  	percpu_down_read(&scx_cgroup_rwsem);
>  
> -	scx_cgroup_warn_missing_weight(tg);
> -
>  	if (scx_cgroup_enabled) {
>  		if (SCX_HAS_OP(cgroup_init)) {
>  			struct scx_cgroup_init_args args =
> @@ -4072,9 +4042,7 @@ void scx_group_set_weight(struct task_gr
>  
>  void scx_group_set_idle(struct task_group *tg, bool idle)
>  {
> -	percpu_down_read(&scx_cgroup_rwsem);
> -	scx_cgroup_warn_missing_idle(tg);
> -	percpu_up_read(&scx_cgroup_rwsem);
> +	/* TODO: Implement ops->cgroup_set_idle() */
>  }
>  
>  static void scx_cgroup_lock(void)
> @@ -4268,9 +4236,6 @@ static int scx_cgroup_init(void)
>  
>  	percpu_rwsem_assert_held(&scx_cgroup_rwsem);
>  
> -	cgroup_warned_missing_weight = false;
> -	cgroup_warned_missing_idle = false;
> -
>  	/*
>  	 * scx_tg_on/offline() are excluded through scx_cgroup_rwsem. If we walk
>  	 * cgroups and init, all online cgroups are initialized.
> @@ -4280,9 +4245,6 @@ static int scx_cgroup_init(void)
>  		struct task_group *tg = css_tg(css);
>  		struct scx_cgroup_init_args args = { .weight = tg->scx_weight };
>  
> -		scx_cgroup_warn_missing_weight(tg);
> -		scx_cgroup_warn_missing_idle(tg);
> -
>  		if ((tg->scx_flags &
>  		     (SCX_TG_ONLINE | SCX_TG_INITED)) != SCX_TG_ONLINE)
>  			continue;