Re: [PATCH 5/6] cgroup/cpuset: Free DL BW in case can_attach() fails

Waiman Long
2023-03-29T14:25:07Z

On 3/29/23 08:55, Juri Lelli wrote:
> From: Dietmar Eggemann <dietmar.eggemann@arm.com>
>
> cpuset_can_attach() can fail. Postpone DL BW allocation until all tasks
> have been checked. DL BW is not allocated per-task but as a sum over
> all DL tasks migrating.
>
> If multiple controllers are attached to the cgroup next to the cuset
Typo: : "cuset" => "cpuset"
> controller a non-cpuset can_attach() can fail. In this case free DL BW
> in cpuset_cancel_attach().
>
> Finally, update cpuset DL task count (nr_deadline_tasks) only in
> cpuset_attach().
>
> Suggested-by: Waiman Long <longman@redhat.com>
> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
> ---
> include/linux/sched.h | 2 +-
> kernel/cgroup/cpuset.c | 55 ++++++++++++++++++++++++++++++++++++++----
> kernel/sched/core.c | 17 ++-----------
> 3 files changed, 53 insertions(+), 21 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 6f3d84e0ed08..50cbbfefbe11 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1847,7 +1847,7 @@ 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 task_can_attach(struct task_struct *p);
> extern int dl_bw_alloc(int cpu, u64 dl_bw);
> extern void dl_bw_free(int cpu, u64 dl_bw);
> #ifdef CONFIG_SMP
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index eb0854ef9757..f8ebec66da51 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -198,6 +198,8 @@ struct cpuset {
> * know when to rebuild associated root domain bandwidth information.
> */
> int nr_deadline_tasks;
> + int nr_migrate_dl_tasks;
> + u64 sum_migrate_dl_bw;
>
> /* Invalid partition error code, not lock protected */
> enum prs_errcode prs_err;
> @@ -2464,16 +2466,23 @@ static int fmeter_getrate(struct fmeter *fmp)
>
> static struct cpuset *cpuset_attach_old_cs;
>
> +static void reset_migrate_dl_data(struct cpuset *cs)
> +{
> + cs->nr_migrate_dl_tasks = 0;
> + cs->sum_migrate_dl_bw = 0;
> +}
> +
> /* Called by cgroups to determine if a cpuset is usable; cpuset_mutex held */
> static int cpuset_can_attach(struct cgroup_taskset *tset)
> {
> struct cgroup_subsys_state *css;
> - struct cpuset *cs;
> + struct cpuset *cs, *oldcs;
> struct task_struct *task;
> int ret;
>
> /* used later by cpuset_attach() */
> cpuset_attach_old_cs = task_cs(cgroup_taskset_first(tset, &css));
> + oldcs = cpuset_attach_old_cs;
> cs = css_cs(css);
>
> mutex_lock(&cpuset_mutex);
> @@ -2491,7 +2500,7 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
> goto out_unlock;
>
> cgroup_taskset_for_each(task, css, tset) {
> - ret = task_can_attach(task, cs->effective_cpus);
> + ret = task_can_attach(task);
> if (ret)
> goto out_unlock;
> ret = security_task_setscheduler(task);
> @@ -2499,11 +2508,31 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
> goto out_unlock;
>
> if (dl_task(task)) {
> - cs->nr_deadline_tasks++;
> - cpuset_attach_old_cs->nr_deadline_tasks--;
> + cs->nr_migrate_dl_tasks++;
> + cs->sum_migrate_dl_bw += task->dl.dl_bw;
> + }
> + }
> +
> + if (!cs->nr_migrate_dl_tasks)
> + goto out_succes;
> +
> + if (!cpumask_intersects(oldcs->effective_cpus, cs->effective_cpus)) {
> + int cpu = cpumask_any_and(cpu_active_mask, cs->effective_cpus);
> +
> + if (unlikely(cpu >= nr_cpu_ids)) {
> + reset_migrate_dl_data(cs);
> + ret = -EINVAL;
> + goto out_unlock;
> + }
> +
> + ret = dl_bw_alloc(cpu, cs->sum_migrate_dl_bw);
> + if (ret) {
> + reset_migrate_dl_data(cs);
> + goto out_unlock;
> }
> }
>
> +out_succes:
> /*
> * Mark attach is in progress. This makes validate_change() fail
> * changes which zero cpus/mems_allowed.
> @@ -2518,11 +2547,21 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
> static void cpuset_cancel_attach(struct cgroup_taskset *tset)
> {
> struct cgroup_subsys_state *css;
> + struct cpuset *cs;
>
> cgroup_taskset_first(tset, &css);
> + cs = css_cs(css);
>
> mutex_lock(&cpuset_mutex);
> - css_cs(css)->attach_in_progress--;
> + cs->attach_in_progress--;
> +
> + if (cs->nr_migrate_dl_tasks) {
> + int cpu = cpumask_any(cs->effective_cpus);
> +
> + dl_bw_free(cpu, cs->sum_migrate_dl_bw);
> + reset_migrate_dl_data(cs);
> + }
> +
> mutex_unlock(&cpuset_mutex);
> }
>
> @@ -2617,6 +2656,12 @@ static void cpuset_attach(struct cgroup_taskset *tset)
> out:
> cs->old_mems_allowed = cpuset_attach_nodemask_to;
>
> + if (cs->nr_migrate_dl_tasks) {
> + cs->nr_deadline_tasks += cs->nr_migrate_dl_tasks;
> + oldcs->nr_deadline_tasks -= cs->nr_migrate_dl_tasks;
> + reset_migrate_dl_data(cs);
> + }
> +
> cs->attach_in_progress--;
> if (!cs->attach_in_progress)
> wake_up(&cpuset_attach_wq);
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index c83dae6b8586..10454980e830 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -9269,8 +9269,7 @@ int cpuset_cpumask_can_shrink(const struct cpumask *cur,
> return ret;
> }
>
> -int task_can_attach(struct task_struct *p,
> - const struct cpumask *cs_effective_cpus)
> +int task_can_attach(struct task_struct *p)
> {
> int ret = 0;
>
> @@ -9283,21 +9282,9 @@ int task_can_attach(struct task_struct *p,
> * success of set_cpus_allowed_ptr() on all attached tasks
> * before cpus_mask may be changed.
> */
> - if (p->flags & PF_NO_SETAFFINITY) {
> + if (p->flags & PF_NO_SETAFFINITY)
> ret = -EINVAL;
> - goto out;
> - }
> -
> - if (dl_task(p) && !cpumask_intersects(task_rq(p)->rd->span,
> - cs_effective_cpus)) {
> - int cpu = cpumask_any_and(cpu_active_mask, cs_effective_cpus);
>
> - if (unlikely(cpu >= nr_cpu_ids))
> - return -EINVAL;
> - ret = dl_bw_alloc(cpu, p->dl.dl_bw);
> - }
> -
> -out:
> return ret;
> }
>