Re: [PATCH v4 7/7] sched/fair: Fair server interface

[Peter Zijlstra]

On Thu, Aug 31, 2023 at 10:28:58PM +0200, Daniel Bristot de Oliveira wrote:
> +static ssize_t
> +sched_fair_server_runtime_write(struct file *filp, const char __user *ubuf,
> +				size_t cnt, loff_t *ppos)
> +{
> +	long cpu = (long) ((struct seq_file *) filp->private_data)->private;
> +	struct rq *rq = cpu_rq(cpu);
> +	unsigned long flags;
> +	u64 runtime;
> +	int err;
> +
> +	err = kstrtoull_from_user(ubuf, cnt, 10, &runtime);
> +	if (err)
> +		return err;
> +
> +	raw_spin_rq_lock_irqsave(rq, flags);
> +	if (runtime > rq->fair_server.dl_period)
> +		err = -EINVAL;
> +	else
> +		rq->fair_server.dl_runtime = runtime;
> +	raw_spin_rq_unlock_irqrestore(rq, flags);
> +
> +	if (err)
> +		return err;
> +
> +	*ppos += cnt;
> +	return cnt;
> +}

> +static ssize_t
> +sched_fair_server_period_write(struct file *filp, const char __user *ubuf,
> +			       size_t cnt, loff_t *ppos)
> +{
> +	long cpu = (long) ((struct seq_file *) filp->private_data)->private;
> +	struct rq *rq = cpu_rq(cpu);
> +	unsigned long flags;
> +	u64 period;
> +	int err;
> +
> +	err = kstrtoull_from_user(ubuf, cnt, 10, &period);
> +	if (err)
> +		return err;
> +
> +	if (period < fair_server_period_min || period > fair_server_period_max)
> +		return -EINVAL;
> +
> +	raw_spin_rq_lock_irqsave(rq, flags);
> +	if (period < rq->fair_server.dl_runtime)
> +		err = -EINVAL;
> +	else
> +		rq->fair_server.dl_period = period;
> +	raw_spin_rq_unlock_irqrestore(rq, flags);
> +
> +	if (err)
> +		return err;
> +
> +	*ppos += cnt;
> +	return cnt;
> +}

> +static ssize_t
> +sched_fair_server_defer_write(struct file *filp, const char __user *ubuf,
> +			      size_t cnt, loff_t *ppos)
> +{
> +	long cpu = (long) ((struct seq_file *) filp->private_data)->private;
> +	struct rq *rq = cpu_rq(cpu);
> +	unsigned long flags;
> +	u64 defer;
> +	int err;
> +
> +	err = kstrtoull_from_user(ubuf, cnt, 10, &defer);
> +	if (err)
> +		return err;
> +
> +	if (defer < 0 || defer > 1)
> +		return -EINVAL;
> +
> +	raw_spin_rq_lock_irqsave(rq, flags);
> +	rq->fair_server_defer = defer;
> +	raw_spin_rq_unlock_irqrestore(rq, flags);
> +
> +	*ppos += cnt;
> +	return cnt;
> +}

Surely we can write a single function that does all of that with less
duplication?

Additionally, should not the deadline parameters be vetted by access
control before being accepted ?

Perhaps something like so:

static ssize_t
sched_fair_server_write(struct file *filp, const char __user *ubuf, size_t cnt, loff_t *ppos, enum dl_param param)
{
	long cpu = (long) ((struct seq_file *) filp->private_data)->private;
	struct rq *rq = cpu_rq(cpu);
	u64 value;

	err = kstrtoull_from_user(ubuf, cnt, 10, &value);
	if (err)
		return err;

	scoped_guard (rq_lock_irqsave, rq) {

		u64 runtime, deadline, period;

		runtime  = rq->fair_server.dl_runtime;
		deadline = rq->fair_server.dl_deadline;
		period   = rq->fair_server.dl_period;

		switch (param) {
			case dl_runtime:  runtime  = value; break;
			case dl_deadline: deadline = value; break;
			case dl_period:   period   = value; break;
		}

		if (runtime > deadline ||
		    deadline > period ||
		    /* more stuff like access controll */)
			return -EINVAL;

		rq->fair_server.dl_runtime  = runtime;
		rq->fair_server.dl_deadline = deadline;
		rq->fair_server.dl_period   = period;
	}

	*ppos += cnt;
	return cnt;
}