Re: [PATCH v8 12/16] sched/core: uclamp: Extend CPU's cgroup controller

[Suren Baghdasaryan]

On Tue, Apr 2, 2019 at 3:43 AM Patrick Bellasi <patrick.bellasi@xxxxxxx> wrote:
>
> The cgroup CPU bandwidth 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.
>
> Giving the mechanisms described above, it is now possible to extend the
> cpu controller to specify the minimum (or maximum) utilization which
> should be considered for tasks RUNNABLE on a cpu.
> This makes it possible to better defined the actual computational
> power assigned to task groups, thus improving the cgroup CPU bandwidth
> controller which is currently based just on time constraints.
>
> Extend the CPU controller with a couple of new attributes util.{min,max}
> which allows to enforce utilization boosting and capping for all the
> tasks in a group. Specifically:
>
> - util.min: defines the minimum utilization which should be considered
>             i.e. the RUNNABLE tasks of this group will run at least at a
>                  minimum frequency which corresponds to the util.min
>                  utilization
>
> - util.max: defines the maximum utilization which should be considered
>             i.e. the RUNNABLE tasks of this group will run up to a
>                  maximum frequency which corresponds to the util.max
>                  utilization
>
> These attributes:
>
> a) are available only for non-root nodes, both on default and legacy
>    hierarchies, while system wide clamps are defined by a generic
>    interface which does not depends on cgroups. This system wide
>    interface enforces constraints on tasks in the root node.
>
> b) enforce effective constraints at each level of the hierarchy which
>    are a restriction of the group requests considering its parent's
>    effective constraints. Root group effective constraints are defined
>    by the system wide interface.
>    This mechanism allows each (non-root) level of the hierarchy to:
>    - request whatever clamp values it would like to get
>    - effectively get only up to the maximum amount allowed by its parent
>
> c) have higher priority than task-specific clamps, defined via
>    sched_setattr(), thus allowing to control and restrict task requests
>
> Add two new attributes to the cpu controller to collect "requested"
> clamp values. Allow that at each non-root level of the hierarchy.
> Validate local consistency by enforcing util.min < util.max.
> Keep it simple by do not caring now about "effective" values computation
> and propagation along the hierarchy.
>
> Signed-off-by: Patrick Bellasi <patrick.bellasi@xxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Tejun Heo <tj@xxxxxxxxxx>
>
> --
> Changes in v8:
>  Message-ID: <20190214154817.GN50184@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
>  - update changelog description for points b), c) and following paragraph
> ---
>  Documentation/admin-guide/cgroup-v2.rst |  27 +++++
>  init/Kconfig                            |  22 ++++
>  kernel/sched/core.c                     | 142 +++++++++++++++++++++++-
>  kernel/sched/sched.h                    |   6 +
>  4 files changed, 196 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index 7bf3f129c68b..47710a77f4fa 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -909,6 +909,12 @@ 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
> @@ -974,6 +980,27 @@ All time durations are in microseconds.
>         Shows pressure stall information for CPU. See
>         Documentation/accounting/psi.txt for details.
>
> +  cpu.util.min
> +        A read-write single value file which exists on non-root cgroups.
> +        The default is "0", i.e. no utilization boosting.
> +
> +        The requested minimum utilization in the range [0, 1024].
> +
> +        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 "1024". i.e. no utilization capping
> +
> +        The requested maximum utilization in the range [0, 1024].
> +
> +        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 7439cbf4d02e..33006e8de996 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -877,6 +877,28 @@ 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 71c9dd6487b1..aeed2dd315cc 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1130,8 +1130,12 @@ static void __init init_uclamp(void)
>         /* System defaults allow max clamp values for both indexes */
>         uc_max.value = uclamp_none(UCLAMP_MAX);
>         uc_max.bucket_id = uclamp_bucket_id(uc_max.value);
> -       for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id)
> +       for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id) {
>                 uclamp_default[clamp_id] = uc_max;
> +#ifdef CONFIG_UCLAMP_TASK_GROUP
> +               root_task_group.uclamp_req[clamp_id] = uc_max;
> +#endif
> +       }
>  }
>
>  #else /* CONFIG_UCLAMP_TASK */
> @@ -6720,6 +6724,19 @@ void ia64_set_curr_task(int cpu, struct task_struct *p)
>  /* task_group_lock serializes the addition/removal of task groups */
>  static DEFINE_SPINLOCK(task_group_lock);
>
> +static inline int alloc_uclamp_sched_group(struct task_group *tg,
> +                                          struct task_group *parent)
> +{
> +#ifdef CONFIG_UCLAMP_TASK_GROUP
> +       int clamp_id;
> +
> +       for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id)
> +               tg->uclamp_req[clamp_id] = parent->uclamp_req[clamp_id];
> +#endif
> +
> +       return 1;

Looks like you never return anything else neither here nor in the
following patches I think...

> +}
> +
>  static void sched_free_group(struct task_group *tg)
>  {
>         free_fair_sched_group(tg);
> @@ -6743,6 +6760,9 @@ 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:
> @@ -6963,6 +6983,100 @@ 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 = 0;
> +
> +       if (min_value > SCHED_CAPACITY_SCALE)
> +               return -ERANGE;
> +
> +       rcu_read_lock();
> +
> +       tg = css_tg(css);
> +       if (tg == &root_task_group) {
> +               ret = -EINVAL;
> +               goto out;
> +       }
> +       if (tg->uclamp_req[UCLAMP_MIN].value == min_value)
> +               goto out;
> +       if (tg->uclamp_req[UCLAMP_MAX].value < min_value) {
> +               ret = -EINVAL;
> +               goto out;
> +       }
> +
> +       /* Update tg's "requested" clamp value */
> +       tg->uclamp_req[UCLAMP_MIN].value = min_value;
> +       tg->uclamp_req[UCLAMP_MIN].bucket_id = uclamp_bucket_id(min_value);
> +
> +out:
> +       rcu_read_unlock();
> +
> +       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 = 0;
> +
> +       if (max_value > SCHED_CAPACITY_SCALE)
> +               return -ERANGE;
> +
> +       rcu_read_lock();
> +
> +       tg = css_tg(css);
> +       if (tg == &root_task_group) {
> +               ret = -EINVAL;
> +               goto out;
> +       }
> +       if (tg->uclamp_req[UCLAMP_MAX].value == max_value)
> +               goto out;
> +       if (tg->uclamp_req[UCLAMP_MIN].value > max_value) {
> +               ret = -EINVAL;
> +               goto out;
> +       }
> +
> +       /* Update tg's "requested" clamp value */
> +       tg->uclamp_req[UCLAMP_MAX].value = max_value;
> +       tg->uclamp_req[UCLAMP_MAX].bucket_id = uclamp_bucket_id(max_value);
> +
> +out:
> +       rcu_read_unlock();
> +
> +       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_req[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)
> @@ -7300,6 +7414,18 @@ 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 */
>  };
> @@ -7467,6 +7593,20 @@ 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 6ae3628248eb..b46b6912beba 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -399,6 +399,12 @@ struct task_group {
>  #endif
>
>         struct cfs_bandwidth    cfs_bandwidth;
> +
> +#ifdef CONFIG_UCLAMP_TASK_GROUP
> +       /* Clamp values requested for a task group */
> +       struct uclamp_se        uclamp_req[UCLAMP_CNT];
> +#endif
> +
>  };
>
>  #ifdef CONFIG_FAIR_GROUP_SCHED
> --
> 2.20.1
>