Re: [PATCH v2 3/6] sched/cpuset: Keep track of SCHED_DEADLINE task in cpusets

Waiman Long
2023-05-03T17:57:15Z

On 5/3/23 03:22, Juri Lelli wrote:
> Qais reported that iterating over all tasks when rebuilding root domains
> for finding out which ones are DEADLINE and need their bandwidth
> correctly restored on such root domains can be a costly operation (10+
> ms delays on suspend-resume).
>
> To fix the problem keep track of the number of DEADLINE tasks belonging
> to each cpuset and then use this information (followup patch) to only
> perform the above iteration if DEADLINE tasks are actually present in
> the cpuset for which a corresponding root domain is being rebuilt.
>
> Reported-by: Qais Yousef <qyousef@layalina.io>
> Link: https://lore.kernel.org/lkml/20230206221428.2125324-1-qyousef@layalina.io/
> Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
> ---
> include/linux/cpuset.h | 4 ++++
> kernel/cgroup/cgroup.c | 4 ++++
> kernel/cgroup/cpuset.c | 25 +++++++++++++++++++++++++
> kernel/sched/deadline.c | 14 ++++++++++++++
> 4 files changed, 47 insertions(+)
>
> diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
> index f90e6325d707..d629094fac6e 100644
> --- a/include/linux/cpuset.h
> +++ b/include/linux/cpuset.h
> @@ -71,6 +71,8 @@ extern void cpuset_init_smp(void);
> extern void cpuset_force_rebuild(void);
> extern void cpuset_update_active_cpus(void);
> extern void cpuset_wait_for_hotplug(void);
> +extern void inc_dl_tasks_cs(struct task_struct *task);
> +extern void dec_dl_tasks_cs(struct task_struct *task);
> extern void cpuset_lock(void);
> extern void cpuset_unlock(void);
> extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
> @@ -189,6 +191,8 @@ static inline void cpuset_update_active_cpus(void)
>
> static inline void cpuset_wait_for_hotplug(void) { }
>
> +static inline void inc_dl_tasks_cs(struct task_struct *task) { }
> +static inline void dec_dl_tasks_cs(struct task_struct *task) { }
> static inline void cpuset_lock(void) { }
> static inline void cpuset_unlock(void) { }
>
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index 625d7483951c..9d809191a54f 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -57,6 +57,7 @@
> #include <linux/file.h>
> #include <linux/fs_parser.h>
> #include <linux/sched/cputime.h>
> +#include <linux/sched/deadline.h>
> #include <linux/psi.h>
> #include <net/sock.h>
>
> @@ -6683,6 +6684,9 @@ void cgroup_exit(struct task_struct *tsk)
> list_add_tail(&tsk->cg_list, &cset->dying_tasks);
> cset->nr_tasks--;
>
> + if (dl_task(tsk))
> + dec_dl_tasks_cs(tsk);
> +
> WARN_ON_ONCE(cgroup_task_frozen(tsk));
> if (unlikely(!(tsk->flags & PF_KTHREAD) &&
> test_bit(CGRP_FREEZE, &task_dfl_cgroup(tsk)->flags)))
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index ee66be215fb9..b9f4d5602517 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -193,6 +193,12 @@ struct cpuset {
> int use_parent_ecpus;
> int child_ecpus_count;
>
> + /*
> + * number of SCHED_DEADLINE tasks attached to this cpuset, so that we
> + * know when to rebuild associated root domain bandwidth information.
> + */
> + int nr_deadline_tasks;
> +
> /* Invalid partition error code, not lock protected */
> enum prs_errcode prs_err;
>
> @@ -245,6 +251,20 @@ static inline struct cpuset *parent_cs(struct cpuset *cs)
> return css_cs(cs->css.parent);
> }
>
> +void inc_dl_tasks_cs(struct task_struct *p)
> +{
> + struct cpuset *cs = task_cs(p);
> +
> + cs->nr_deadline_tasks++;
> +}
> +
> +void dec_dl_tasks_cs(struct task_struct *p)
> +{
> + struct cpuset *cs = task_cs(p);
> +
> + cs->nr_deadline_tasks--;
> +}
> +
> /* bits in struct cpuset flags field */
> typedef enum {
> CS_ONLINE,
> @@ -2497,6 +2517,11 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
> ret = security_task_setscheduler(task);
> if (ret)
> goto out_unlock;
> +
> + if (dl_task(task)) {
> + cs->nr_deadline_tasks++;
> + cpuset_attach_old_cs->nr_deadline_tasks--;
> + }
> }
>
> /*
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 5a9a4b81c972..e11de074a6fd 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -16,6 +16,8 @@
> * Fabio Checconi <fchecconi@gmail.com>
> */
>
> +#include <linux/cpuset.h>
> +
> /*
> * Default limits for DL period; on the top end we guard against small util
> * tasks still getting ridiculously long effective runtimes, on the bottom end we
> @@ -2596,6 +2598,12 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p)
> if (task_on_rq_queued(p) && p->dl.dl_runtime)
> task_non_contending(p);
>
> + /*
> + * In case a task is setscheduled out from SCHED_DEADLINE we need to
> + * keep track of that on its cpuset (for correct bandwidth tracking).
> + */
> + dec_dl_tasks_cs(p);
> +
> if (!task_on_rq_queued(p)) {
> /*
> * Inactive timer is armed. However, p is leaving DEADLINE and
> @@ -2636,6 +2644,12 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
> if (hrtimer_try_to_cancel(&p->dl.inactive_timer) == 1)
> put_task_struct(p);
>
> + /*
> + * In case a task is setscheduled to SCHED_DEADLINE we need to keep
> + * track of that on its cpuset (for correct bandwidth tracking).
> + */
> + inc_dl_tasks_cs(p);
> +
> /* If p is not queued we will update its parameters at next wakeup. */
> if (!task_on_rq_queued(p)) {
> add_rq_bw(&p->dl, &rq->dl);
Reviewed-by: Waiman Long <longman@redhat.com>