Re: [PATCH v2 08/12] sched/core: uclamp: extend cpu's cgroup controller

[Suren Baghdasaryan <surenb@google.com>]

On Mon, Jul 16, 2018 at 1:29 AM, Patrick Bellasi
<patrick.bellasi@arm.com> wrote:
> The cgroup's CPU controller allows to assign a specified (maximum)
> bandwidth to the tasks of a group. However this bandwidth is defined and
> enforced only on a temporal base, without considering the actual
> frequency a CPU is running on. Thus, the amount of computation completed
> by a task within an allocated bandwidth can be very different depending
> on the actual frequency the CPU is running that task.
> The amount of computation can be affected also by the specific CPU a
> task is running on, especially when running on asymmetric capacity
> systems like Arm's big.LITTLE.
>
> With the availability of schedutil, the scheduler is now able
> to drive frequency selections based on actual task utilization.
> Moreover, the utilization clamping support provides a mechanism to
> bias the frequency selection operated by schedutil depending on
> constraints assigned to the tasks currently RUNNABLE on a CPU.
>
> Give the above mechanisms, it is now possible to extend the cpu
> controller to specify what is the minimum (or maximum) utilization which
> a task is expected (or allowed) to generate.
> Constraints on minimum and maximum utilization allowed for tasks in a
> CPU cgroup can improve the control on the actual amount of CPU bandwidth
> consumed by tasks.
>
> Utilization clamping constraints are useful not only to bias frequency
> selection, when a task is running, but also to better support certain
> scheduler decisions regarding task placement. For example, on
> asymmetric capacity systems, a utilization clamp value can be
> conveniently used to enforce important interactive tasks on more capable
> CPUs or to run low priority and background tasks on more energy
> efficient CPUs.
>
> The ultimate goal of utilization clamping is thus to enable:
>
> - boosting: by selecting an higher capacity CPU and/or higher execution
>             frequency for small tasks which are affecting the user
>             interactive experience.
>
> - capping: by selecting more energy efficiency CPUs or lower execution
>            frequency, for big tasks which are mainly related to
>            background activities, and thus without a direct impact on
>            the user experience.
>
> Thus, a proper extension of the cpu controller with utilization clamping
> support will make this controller even more suitable for integration
> with advanced system management software (e.g. Android).
> Indeed, an informed user-space can provide rich information hints to the
> scheduler regarding the tasks it's going to schedule.
>
> This patch extends the CPU controller by adding a couple of new
> attributes, util_min and util_max, which can be used to enforce task's
> utilization boosting and capping. Specifically:
>
> - util_min: defines the minimum utilization which should be considered,
>             e.g. when schedutil selects the frequency for a CPU while a
>             task in this group is RUNNABLE.
>             i.e. the task will run at least at a minimum frequency which
>                 corresponds to the min_util utilization
>
> - util_max: defines the maximum utilization which should be considered,
>             e.g. when schedutil selects the frequency for a CPU while a
>             task in this group is RUNNABLE.
>             i.e. the task will run up to a maximum frequency which
>                 corresponds to the max_util utilization
>
> These attributes:
>
> a) are available only for non-root nodes, both on default and legacy
>    hierarchies
> b) do not enforce any constraints and/or dependency between the parent
>    and its child nodes, thus relying on the delegation model and
>    permission settings defined by the system management software
> c) allow to (eventually) further restrict task-specific clamps defined
>    via sched_setattr(2)
>
> This patch provides the basic support to expose the two new attributes
> and to validate their run-time updates.
>
> Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Cc: Viresh Kumar <viresh.kumar@linaro.org>
> Cc: Todd Kjos <tkjos@google.com>
> Cc: Joel Fernandes <joelaf@google.com>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-pm@vger.kernel.org
> ---
>  Documentation/admin-guide/cgroup-v2.rst |  25 ++++
>  init/Kconfig                            |  22 +++
>  kernel/sched/core.c                     | 186 ++++++++++++++++++++++++
>  kernel/sched/sched.h                    |   5 +
>  4 files changed, 238 insertions(+)
>
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index 8a2c52d5c53b..328c011cc105 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -904,6 +904,12 @@ controller implements weight and absolute bandwidth limit models for
>  normal scheduling policy and absolute bandwidth allocation model for
>  realtime scheduling policy.
>
> +Cycles distribution is based, by default, on a temporal base and it
> +does not account for the frequency at which tasks are executed.
> +The (optional) utilization clamping support allows to enforce a minimum
> +bandwidth, which should always be provided by a CPU, and a maximum bandwidth,
> +which should never be exceeded by a CPU.
> +
>  WARNING: cgroup2 doesn't yet support control of realtime processes and
>  the cpu controller can only be enabled when all RT processes are in
>  the root cgroup.  Be aware that system management software may already
> @@ -963,6 +969,25 @@ All time durations are in microseconds.
>         $PERIOD duration.  "max" for $MAX indicates no limit.  If only
>         one number is written, $MAX is updated.
>
> +  cpu.util_min
> +        A read-write single value file which exists on non-root cgroups.
> +        The default is "0", i.e. no bandwidth boosting.
> +
> +        The minimum utilization in the range [0, 1023].
> +
> +        This interface allows reading and setting minimum utilization clamp
> +        values similar to the sched_setattr(2). This minimum utilization
> +        value is used to clamp the task specific minimum utilization clamp.
> +
> +  cpu.util_max
> +        A read-write single value file which exists on non-root cgroups.
> +        The default is "1023". i.e. no bandwidth clamping
> +
> +        The maximum utilization in the range [0, 1023].
> +
> +        This interface allows reading and setting maximum utilization clamp
> +        values similar to the sched_setattr(2). This maximum utilization
> +        value is used to clamp the task specific maximum utilization clamp.
>
>  Memory
>  ------
> diff --git a/init/Kconfig b/init/Kconfig
> index 0a377ad7c166..d7e2b74637ff 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -792,6 +792,28 @@ config RT_GROUP_SCHED
>
>  endif #CGROUP_SCHED
>
> +config UCLAMP_TASK_GROUP
> +       bool "Utilization clamping per group of tasks"
> +       depends on CGROUP_SCHED
> +       depends on UCLAMP_TASK
> +       default n
> +       help
> +         This feature enables the scheduler to track the clamped utilization
> +         of each CPU based on RUNNABLE tasks currently scheduled on that CPU.
> +
> +         When this option is enabled, the user can specify a min and max
> +         CPU bandwidth which is allowed for each single task in a group.
> +         The max bandwidth allows to clamp the maximum frequency a task
> +         can use, while the min bandwidth allows to define a minimum
> +         frequency a task will always use.
> +
> +         When task group based utilization clamping is enabled, an eventually
> +          specified task-specific clamp value is constrained by the cgroup
> +         specified clamp value. Both minimum and maximum task clamping cannot
> +          be bigger than the corresponding clamping defined at task group level.
> +
> +         If in doubt, say N.
> +
>  config CGROUP_PIDS
>         bool "PIDs controller"
>         help
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 0cb6e0aa4faa..30b1d894f978 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1227,6 +1227,74 @@ static inline int uclamp_group_get(struct task_struct *p,
>         return 0;
>  }
>
> +#ifdef CONFIG_UCLAMP_TASK_GROUP
> +/**
> + * init_uclamp_sched_group: initialize data structures required for TG's
> + *                          utilization clamping
> + */
> +static inline void init_uclamp_sched_group(void)
> +{
> +       struct uclamp_map *uc_map;
> +       struct uclamp_se *uc_se;
> +       int group_id;
> +       int clamp_id;
> +
> +       /* Root TG's is statically assigned to the first clamp group */
> +       group_id = 0;
> +
> +       /* Initialize root TG's to default (none) clamp values */
> +       for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id) {
> +               uc_map = &uclamp_maps[clamp_id][0];
> +
> +               /* Map root TG's clamp value */
> +               uclamp_group_init(clamp_id, group_id, uclamp_none(clamp_id));
> +
> +               /* Init root TG's clamp group */
> +               uc_se = &root_task_group.uclamp[clamp_id];
> +               uc_se->value = uclamp_none(clamp_id);
> +               uc_se->group_id = group_id;
> +
> +               /* Attach root TG's clamp group */
> +               uc_map[group_id].se_count = 1;
> +       }
> +}
> +
> +/**
> + * alloc_uclamp_sched_group: initialize a new TG's for utilization clamping
> + * @tg: the newly created task group
> + * @parent: its parent task group
> + *
> + * A newly created task group inherits its utilization clamp values, for all
> + * clamp indexes, from its parent task group.
> + * This ensures that its values are properly initialized and that the task
> + * group is accounted in the same parent's group index.
> + *
> + * Return: !0 on error
> + */
> +static inline int alloc_uclamp_sched_group(struct task_group *tg,
> +                                          struct task_group *parent)
> +{
> +       struct uclamp_se *uc_se;
> +       int clamp_id;
> +
> +       for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id) {
> +               uc_se = &tg->uclamp[clamp_id];
> +
> +               uc_se->value = parent->uclamp[clamp_id].value;
> +               uc_se->group_id = UCLAMP_NONE;
> +       }
> +
> +       return 1;
> +}
> +#else /* CONFIG_UCLAMP_TASK_GROUP */
> +static inline void init_uclamp_sched_group(void) { }
> +static inline int alloc_uclamp_sched_group(struct task_group *tg,
> +                                          struct task_group *parent)
> +{
> +       return 1;
> +}
> +#endif /* CONFIG_UCLAMP_TASK_GROUP */
> +
>  static inline int __setscheduler_uclamp(struct task_struct *p,
>                                         const struct sched_attr *attr)
>  {
> @@ -1289,11 +1357,18 @@ static void __init init_uclamp(void)
>                         raw_spin_lock_init(&uc_map[group_id].se_lock);
>                 }
>         }
> +
> +       init_uclamp_sched_group();
>  }
>
>  #else /* CONFIG_UCLAMP_TASK */
>  static inline void uclamp_cpu_get(struct rq *rq, struct task_struct *p) { }
>  static inline void uclamp_cpu_put(struct rq *rq, struct task_struct *p) { }
> +static inline int alloc_uclamp_sched_group(struct task_group *tg,
> +                                          struct task_group *parent)
> +{
> +       return 1;
> +}
>  static inline int __setscheduler_uclamp(struct task_struct *p,
>                                         const struct sched_attr *attr)
>  {
> @@ -6890,6 +6965,9 @@ struct task_group *sched_create_group(struct task_group *parent)
>         if (!alloc_rt_sched_group(tg, parent))
>                 goto err;
>
> +       if (!alloc_uclamp_sched_group(tg, parent))
> +               goto err;
> +
>         return tg;
>
>  err:
> @@ -7110,6 +7188,88 @@ static void cpu_cgroup_attach(struct cgroup_taskset *tset)
>                 sched_move_task(task);
>  }
>
> +#ifdef CONFIG_UCLAMP_TASK_GROUP
> +static int cpu_util_min_write_u64(struct cgroup_subsys_state *css,
> +                                 struct cftype *cftype, u64 min_value)
> +{
> +       struct task_group *tg;
> +       int ret = -EINVAL;
> +
> +       if (min_value > SCHED_CAPACITY_SCALE)
> +               return -ERANGE;
> +
> +       mutex_lock(&uclamp_mutex);
> +       rcu_read_lock();
> +
> +       tg = css_tg(css);
> +       if (tg->uclamp[UCLAMP_MIN].value == min_value) {
> +               ret = 0;
> +               goto out;
> +       }
> +       if (tg->uclamp[UCLAMP_MAX].value < min_value)
> +               goto out;
> +

+ tg->uclamp[UCLAMP_MIN].value = min_value;
+ ret = 0;

Are these assignments missing or am I missing something? Same for
cpu_util_max_write_u64().

> +out:
> +       rcu_read_unlock();
> +       mutex_unlock(&uclamp_mutex);
> +
> +       return ret;
> +}
> +
> +static int cpu_util_max_write_u64(struct cgroup_subsys_state *css,
> +                                 struct cftype *cftype, u64 max_value)
> +{
> +       struct task_group *tg;
> +       int ret = -EINVAL;
> +
> +       if (max_value > SCHED_CAPACITY_SCALE)
> +               return -ERANGE;
> +
> +       mutex_lock(&uclamp_mutex);
> +       rcu_read_lock();
> +
> +       tg = css_tg(css);
> +       if (tg->uclamp[UCLAMP_MAX].value == max_value) {
> +               ret = 0;
> +               goto out;
> +       }
> +       if (tg->uclamp[UCLAMP_MIN].value > max_value)
> +               goto out;
> +
> +out:
> +       rcu_read_unlock();
> +       mutex_unlock(&uclamp_mutex);
> +
> +       return ret;
> +}
> +
> +static inline u64 cpu_uclamp_read(struct cgroup_subsys_state *css,
> +                                 enum uclamp_id clamp_id)
> +{
> +       struct task_group *tg;
> +       u64 util_clamp;
> +
> +       rcu_read_lock();
> +       tg = css_tg(css);
> +       util_clamp = tg->uclamp[clamp_id].value;
> +       rcu_read_unlock();
> +
> +       return util_clamp;
> +}
> +
> +static u64 cpu_util_min_read_u64(struct cgroup_subsys_state *css,
> +                                struct cftype *cft)
> +{
> +       return cpu_uclamp_read(css, UCLAMP_MIN);
> +}
> +
> +static u64 cpu_util_max_read_u64(struct cgroup_subsys_state *css,
> +                                struct cftype *cft)
> +{
> +       return cpu_uclamp_read(css, UCLAMP_MAX);
> +}
> +#endif /* CONFIG_UCLAMP_TASK_GROUP */
> +
>  #ifdef CONFIG_FAIR_GROUP_SCHED
>  static int cpu_shares_write_u64(struct cgroup_subsys_state *css,
>                                 struct cftype *cftype, u64 shareval)
> @@ -7437,6 +7597,18 @@ static struct cftype cpu_legacy_files[] = {
>                 .read_u64 = cpu_rt_period_read_uint,
>                 .write_u64 = cpu_rt_period_write_uint,
>         },
> +#endif
> +#ifdef CONFIG_UCLAMP_TASK_GROUP
> +       {
> +               .name = "util_min",
> +               .read_u64 = cpu_util_min_read_u64,
> +               .write_u64 = cpu_util_min_write_u64,
> +       },
> +       {
> +               .name = "util_max",
> +               .read_u64 = cpu_util_max_read_u64,
> +               .write_u64 = cpu_util_max_write_u64,
> +       },
>  #endif
>         { }     /* Terminate */
>  };
> @@ -7604,6 +7776,20 @@ static struct cftype cpu_files[] = {
>                 .seq_show = cpu_max_show,
>                 .write = cpu_max_write,
>         },
> +#endif
> +#ifdef CONFIG_UCLAMP_TASK_GROUP
> +       {
> +               .name = "util_min",
> +               .flags = CFTYPE_NOT_ON_ROOT,
> +               .read_u64 = cpu_util_min_read_u64,
> +               .write_u64 = cpu_util_min_write_u64,
> +       },
> +       {
> +               .name = "util_max",
> +               .flags = CFTYPE_NOT_ON_ROOT,
> +               .read_u64 = cpu_util_max_read_u64,
> +               .write_u64 = cpu_util_max_write_u64,
> +       },
>  #endif
>         { }     /* terminate */
>  };
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 7e4f10c507b7..1471a23e8f57 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -389,6 +389,11 @@ struct task_group {
>  #endif
>
>         struct cfs_bandwidth    cfs_bandwidth;
> +
> +#ifdef CONFIG_UCLAMP_TASK_GROUP
> +       struct                  uclamp_se uclamp[UCLAMP_CNT];
> +#endif
> +
>  };
>
>  #ifdef CONFIG_FAIR_GROUP_SCHED
> --
> 2.17.1
>