linux-kernel - Re: [PATCH v4 3/4] sched: Allow sched_{get,set}attr to change latency

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Date:   Tue, 25 Feb 2020 12:24:09 +0530
From:   Pavan Kondeti <pkondeti@...eaurora.org>
To:     Parth Shah <parth@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        mingo@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, qais.yousef@....com,
        chris.hyser@...cle.com, patrick.bellasi@...bug.net,
        valentin.schneider@....com, David.Laight@...LAB.COM,
        pjt@...gle.com, pavel@....cz, tj@...nel.org,
        dhaval.giani@...cle.com, qperret@...gle.com,
        tim.c.chen@...ux.intel.com
Subject: Re: [PATCH v4 3/4] sched: Allow sched_{get,set}attr to change
 latency_nice of the task

On Mon, Feb 24, 2020 at 02:29:17PM +0530, Parth Shah wrote:

[...]

> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 65b6c00d6dac..e1dc536d4ca3 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4723,6 +4723,8 @@ static void __setscheduler_params(struct task_struct *p,
>  	p->rt_priority = attr->sched_priority;
>  	p->normal_prio = normal_prio(p);
>  	set_load_weight(p, true);
> +
> +	p->latency_nice = attr->sched_latency_nice;
>  }

We don't want this when SCHED_FLAG_LATENCY_NICE is not set in
attr->flags.

The user may pass SCHED_FLAG_KEEP_PARAMS | SCHED_FLAG_LATENCY_NICE to
change only latency nice value. So we have to update latency_nice
outside __setscheduler_params(), I think.

>  
>  /* Actually do priority change: must hold pi & rq lock. */
> @@ -4880,6 +4882,13 @@ static int __sched_setscheduler(struct task_struct *p,
>  			return retval;
>  	}
>  
> +	if (attr->sched_flags & SCHED_FLAG_LATENCY_NICE) {
> +		if (attr->sched_latency_nice > MAX_LATENCY_NICE)
> +			return -EINVAL;
> +		if (attr->sched_latency_nice < MIN_LATENCY_NICE)
> +			return -EINVAL;
> +	}
> +
>  	if (pi)
>  		cpuset_read_lock();
>  
> @@ -4914,6 +4923,9 @@ static int __sched_setscheduler(struct task_struct *p,
>  			goto change;
>  		if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)
>  			goto change;
> +		if (attr->sched_flags & SCHED_FLAG_LATENCY_NICE &&
> +		    attr->sched_latency_nice != p->latency_nice)
> +			goto change;
>  
>  		p->sched_reset_on_fork = reset_on_fork;
>  		retval = 0;
> @@ -5162,6 +5174,9 @@ static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *a
>  	    size < SCHED_ATTR_SIZE_VER1)
>  		return -EINVAL;
>  
> +	if ((attr->sched_flags & SCHED_FLAG_LATENCY_NICE) &&
> +	    size < SCHED_ATTR_SIZE_VER2)
> +		return -EINVAL;
>  	/*
>  	 * XXX: Do we want to be lenient like existing syscalls; or do we want
>  	 * to be strict and return an error on out-of-bounds values?
> @@ -5391,6 +5406,8 @@ SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
>  	else
>  		kattr.sched_nice = task_nice(p);
>  
> +	kattr.sched_latency_nice = p->latency_nice;
> +

Can you consider printing latency_nice value in proc_sched_show_task() in this
patch/series?

Thanks,
Pavan

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