Re: [PATCH 3/9] sched/vtime: Handle nice updates under vtime

[Peter Zijlstra <peterz@infradead.org>]

On Wed, Nov 06, 2019 at 04:08:01AM +0100, Frederic Weisbecker wrote:
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 7880f4f64d0e..fa56a1bdd5d8 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4488,6 +4488,7 @@ void set_user_nice(struct task_struct *p, long nice)
>  	int old_prio, delta;
>  	struct rq_flags rf;
>  	struct rq *rq;
> +	int old_static;
>  
>  	if (task_nice(p) == nice || nice < MIN_NICE || nice > MAX_NICE)
>  		return;
> @@ -4498,6 +4499,8 @@ void set_user_nice(struct task_struct *p, long nice)
>  	rq = task_rq_lock(p, &rf);
>  	update_rq_clock(rq);
>  
> +	old_static = p->static_prio;
> +
>  	/*
>  	 * The RT priorities are set via sched_setscheduler(), but we still
>  	 * allow the 'normal' nice value to be set - but as expected
> @@ -4532,7 +4535,9 @@ void set_user_nice(struct task_struct *p, long nice)
>  	}
>  	if (running)
>  		set_next_task(rq, p);
> +
>  out_unlock:
> +	vtime_set_nice(rq, p, old_static);
>  	task_rq_unlock(rq, p, &rf);
>  }
>  EXPORT_SYMBOL(set_user_nice);
> @@ -4668,8 +4673,8 @@ static struct task_struct *find_process_by_pid(pid_t pid)
>   */
>  #define SETPARAM_POLICY	-1
>  
> -static void __setscheduler_params(struct task_struct *p,
> -		const struct sched_attr *attr)
> +static void __setscheduler_params(struct rq *rq, struct task_struct *p,
> +				  const struct sched_attr *attr)
>  {
>  	int policy = attr->sched_policy;
>  
> @@ -4680,8 +4685,11 @@ static void __setscheduler_params(struct task_struct *p,
>  
>  	if (dl_policy(policy))
>  		__setparam_dl(p, attr);
> -	else if (fair_policy(policy))
> +	else if (fair_policy(policy)) {
> +		int old_prio = p->static_prio;
>  		p->static_prio = NICE_TO_PRIO(attr->sched_nice);
> +		vtime_set_nice(rq, p, old_prio);
> +	}
>  
>  	/*
>  	 * __sched_setscheduler() ensures attr->sched_priority == 0 when
> @@ -4704,7 +4712,7 @@ static void __setscheduler(struct rq *rq, struct task_struct *p,
>  	if (attr->sched_flags & SCHED_FLAG_KEEP_PARAMS)
>  		return;
>  
> -	__setscheduler_params(p, attr);
> +	__setscheduler_params(rq, p, attr);
>  
>  	/*
>  	 * Keep a potential priority boosting if called from

Would it make sense to add a helper like:

static void
__sched_set_nice(struct rq *rq, struct task_struct *t, long nice)
{
	int old_prio;

	old_prio = t->static_prio;
	t->static_prio = NICE_TO_PRIO(nice);
	vtime_set_nice(rq, t, old_prio);
}