Re: [PATCH 4/6] sched/deadline: Create DL BW alloc, free & check overflow interface

[Waiman Long]

On 3/29/23 08:55, Juri Lelli wrote:
> From: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
>
> Rework the existing dl_cpu_busy() interface which offers DL BW overflow
> checking and per-task DL BW allocation.
>
> Add dl_bw_free() as an interface to be able to free DL BW.
> It will be used to allow freeing of the DL BW request done during
> cpuset_can_attach() in case multiple controllers are attached to the
> cgroup next to the cpuset controller and one of the non-cpuset
> can_attach() fails.
>
> dl_bw_alloc() (and dl_bw_free()) now take a `u64 dl_bw` parameter
> instead of `struct task_struct *p` used in dl_cpu_busy().  This allows
> to allocate DL BW for a set of tasks too rater than only for a single
Typo: "rater" => "rather"
> task.
>
> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
> Signed-off-by: Juri Lelli <juri.lelli@xxxxxxxxxx>
> ---
>   include/linux/sched.h   |  2 ++
>   kernel/sched/core.c     |  4 ++--
>   kernel/sched/deadline.c | 53 +++++++++++++++++++++++++++++++----------
>   kernel/sched/sched.h    |  2 +-
>   4 files changed, 45 insertions(+), 16 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 6d654eb4cabd..6f3d84e0ed08 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1848,6 +1848,8 @@ current_restore_flags(unsigned long orig_flags, unsigned long flags)
>   
>   extern int cpuset_cpumask_can_shrink(const struct cpumask *cur, const struct cpumask *trial);
>   extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_effective_cpus);
> +extern int dl_bw_alloc(int cpu, u64 dl_bw);
> +extern void dl_bw_free(int cpu, u64 dl_bw);
>   #ifdef CONFIG_SMP
>   extern void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask);
>   extern int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask);
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 179266ff653f..c83dae6b8586 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -9294,7 +9294,7 @@ int task_can_attach(struct task_struct *p,
>   
>   		if (unlikely(cpu >= nr_cpu_ids))
>   			return -EINVAL;
> -		ret = dl_cpu_busy(cpu, p);
> +		ret = dl_bw_alloc(cpu, p->dl.dl_bw);
>   	}
>   
>   out:
> @@ -9579,7 +9579,7 @@ static void cpuset_cpu_active(void)
>   static int cpuset_cpu_inactive(unsigned int cpu)
>   {
>   	if (!cpuhp_tasks_frozen) {
> -		int ret = dl_cpu_busy(cpu, NULL);
> +		int ret = dl_bw_check_overflow(cpu);
>   
>   		if (ret)
>   			return ret;
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 8f92f0f87383..5b6965e0e537 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -3057,26 +3057,38 @@ int dl_cpuset_cpumask_can_shrink(const struct cpumask *cur,
>   	return ret;
>   }
>   
> -int dl_cpu_busy(int cpu, struct task_struct *p)
> +enum dl_bw_request {
> +	dl_bw_req_check_overflow = 0,
> +	dl_bw_req_alloc,
> +	dl_bw_req_free
> +};
> +
> +static int dl_bw_manage(enum dl_bw_request req, int cpu, u64 dl_bw)
>   {
> -	unsigned long flags, cap;
> +	unsigned long flags;
>   	struct dl_bw *dl_b;
> -	bool overflow;
> +	bool overflow = 0;
>   
>   	rcu_read_lock_sched();
>   	dl_b = dl_bw_of(cpu);
>   	raw_spin_lock_irqsave(&dl_b->lock, flags);
> -	cap = dl_bw_capacity(cpu);
> -	overflow = __dl_overflow(dl_b, cap, 0, p ? p->dl.dl_bw : 0);
>   
> -	if (!overflow && p) {
> -		/*
> -		 * We reserve space for this task in the destination
> -		 * root_domain, as we can't fail after this point.
> -		 * We will free resources in the source root_domain
> -		 * later on (see set_cpus_allowed_dl()).
> -		 */
> -		__dl_add(dl_b, p->dl.dl_bw, dl_bw_cpus(cpu));
> +	if (req == dl_bw_req_free) {
> +		__dl_sub(dl_b, dl_bw, dl_bw_cpus(cpu));
> +	} else {
> +		unsigned long cap = dl_bw_capacity(cpu);
> +
> +		overflow = __dl_overflow(dl_b, cap, 0, dl_bw);
> +
> +		if (req == dl_bw_req_alloc && !overflow) {
> +			/*
> +			 * We reserve space in the destination
> +			 * root_domain, as we can't fail after this point.
> +			 * We will free resources in the source root_domain
> +			 * later on (see set_cpus_allowed_dl()).
> +			 */
> +			__dl_add(dl_b, dl_bw, dl_bw_cpus(cpu));
> +		}
>   	}
>   
>   	raw_spin_unlock_irqrestore(&dl_b->lock, flags);
> @@ -3084,6 +3096,21 @@ int dl_cpu_busy(int cpu, struct task_struct *p)
>   
>   	return overflow ? -EBUSY : 0;
>   }
> +
> +int dl_bw_check_overflow(int cpu)
> +{
> +	return dl_bw_manage(dl_bw_req_check_overflow, cpu, 0);
> +}
> +
> +int dl_bw_alloc(int cpu, u64 dl_bw)
> +{
> +	return dl_bw_manage(dl_bw_req_alloc, cpu, dl_bw);
> +}
> +
> +void dl_bw_free(int cpu, u64 dl_bw)
> +{
> +	dl_bw_manage(dl_bw_req_free, cpu, dl_bw);
> +}
>   #endif
>   
>   #ifdef CONFIG_SCHED_DEBUG
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 060616944d7a..81ecfd1a1a48 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -330,7 +330,7 @@ extern void __getparam_dl(struct task_struct *p, struct sched_attr *attr);
>   extern bool __checkparam_dl(const struct sched_attr *attr);
>   extern bool dl_param_changed(struct task_struct *p, const struct sched_attr *attr);
>   extern int  dl_cpuset_cpumask_can_shrink(const struct cpumask *cur, const struct cpumask *trial);
> -extern int  dl_cpu_busy(int cpu, struct task_struct *p);
> +extern int  dl_bw_check_overflow(int cpu);
>   
>   #ifdef CONFIG_CGROUP_SCHED
>