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SubjectRe: [PATCH v8 06/16] sched/core: uclamp: Extend sched_setattr() to support utilization clamping
On Tue, Apr 2, 2019 at 3:42 AM Patrick Bellasi <patrick.bellasi@arm.com> wrote:
>
> The SCHED_DEADLINE scheduling class provides an advanced and formal
> model to define tasks requirements that can translate into proper
> decisions for both task placements and frequencies selections. Other
> classes have a more simplified model based on the POSIX concept of
> priorities.
>
> Such a simple priority based model however does not allow to exploit
> most advanced features of the Linux scheduler like, for example, driving
> frequencies selection via the schedutil cpufreq governor. However, also
> for non SCHED_DEADLINE tasks, it's still interesting to define tasks
> properties to support scheduler decisions.
>
> Utilization clamping exposes to user-space a new set of per-task
> attributes the scheduler can use as hints about the expected/required
> utilization for a task. This allows to implement a "proactive" per-task
> frequency control policy, a more advanced policy than the current one
> based just on "passive" measured task utilization. For example, it's
> possible to boost interactive tasks (e.g. to get better performance) or
> cap background tasks (e.g. to be more energy/thermal efficient).
>
> Introduce a new API to set utilization clamping values for a specified
> task by extending sched_setattr(), a syscall which already allows to
> define task specific properties for different scheduling classes. A new
> pair of attributes allows to specify a minimum and maximum utilization
> the scheduler can consider for a task.
>
> Do that by validating the required clamp values before and then applying
> the required changes using _the_ same pattern already in use for
> __setscheduler(). This ensures that the task is re-enqueued with the new
> clamp values.
>
> Do not allow to change sched class specific params and non class
> specific params (i.e. clamp values) at the same time. This keeps things
> simple and still works for the most common cases since we are usually
> interested in just one of the two actions.

Sorry, I can't find where you are checking to eliminate the
possibility of simultaneous changes to both sched class specific
params and non class specific params... Am I too tired or they are
indeed missing?

>
> Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
>
> ---
> Changes in v8:
> Others:
> - using p->uclamp_req to track clamp values "requested" from userspace
> ---
> include/linux/sched.h | 9 ++++
> include/uapi/linux/sched.h | 12 ++++-
> include/uapi/linux/sched/types.h | 66 ++++++++++++++++++++----
> kernel/sched/core.c | 87 +++++++++++++++++++++++++++++++-
> 4 files changed, 162 insertions(+), 12 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index d8491954e2e1..c2b81a84985b 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -585,6 +585,7 @@ struct sched_dl_entity {
> * @value: clamp value "assigned" to a se
> * @bucket_id: bucket index corresponding to the "assigned" value
> * @active: the se is currently refcounted in a rq's bucket
> + * @user_defined: the requested clamp value comes from user-space
> *
> * The bucket_id is the index of the clamp bucket matching the clamp value
> * which is pre-computed and stored to avoid expensive integer divisions from
> @@ -594,11 +595,19 @@ struct sched_dl_entity {
> * which can be different from the clamp value "requested" from user-space.
> * This allows to know a task is refcounted in the rq's bucket corresponding
> * to the "effective" bucket_id.
> + *
> + * The user_defined bit is set whenever a task has got a task-specific clamp
> + * value requested from userspace, i.e. the system defaults apply to this task
> + * just as a restriction. This allows to relax default clamps when a less
> + * restrictive task-specific value has been requested, thus allowing to
> + * implement a "nice" semantic. For example, a task running with a 20%
> + * default boost can still drop its own boosting to 0%.
> */
> struct uclamp_se {
> unsigned int value : bits_per(SCHED_CAPACITY_SCALE);
> unsigned int bucket_id : bits_per(UCLAMP_BUCKETS);
> unsigned int active : 1;
> + unsigned int user_defined : 1;
> };
> #endif /* CONFIG_UCLAMP_TASK */
>
> diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
> index 075c610adf45..d2c65617a4a4 100644
> --- a/include/uapi/linux/sched.h
> +++ b/include/uapi/linux/sched.h
> @@ -53,10 +53,20 @@
> #define SCHED_FLAG_RECLAIM 0x02
> #define SCHED_FLAG_DL_OVERRUN 0x04
> #define SCHED_FLAG_KEEP_POLICY 0x08
> +#define SCHED_FLAG_KEEP_PARAMS 0x10
> +#define SCHED_FLAG_UTIL_CLAMP_MIN 0x20
> +#define SCHED_FLAG_UTIL_CLAMP_MAX 0x40
> +
> +#define SCHED_FLAG_KEEP_ALL (SCHED_FLAG_KEEP_POLICY | \
> + SCHED_FLAG_KEEP_PARAMS)
> +
> +#define SCHED_FLAG_UTIL_CLAMP (SCHED_FLAG_UTIL_CLAMP_MIN | \
> + SCHED_FLAG_UTIL_CLAMP_MAX)
>
> #define SCHED_FLAG_ALL (SCHED_FLAG_RESET_ON_FORK | \
> SCHED_FLAG_RECLAIM | \
> SCHED_FLAG_DL_OVERRUN | \
> - SCHED_FLAG_KEEP_POLICY)
> + SCHED_FLAG_KEEP_ALL | \
> + SCHED_FLAG_UTIL_CLAMP)
>
> #endif /* _UAPI_LINUX_SCHED_H */
> diff --git a/include/uapi/linux/sched/types.h b/include/uapi/linux/sched/types.h
> index 10fbb8031930..c852153ddb0d 100644
> --- a/include/uapi/linux/sched/types.h
> +++ b/include/uapi/linux/sched/types.h
> @@ -9,6 +9,7 @@ struct sched_param {
> };
>
> #define SCHED_ATTR_SIZE_VER0 48 /* sizeof first published struct */
> +#define SCHED_ATTR_SIZE_VER1 56 /* add: util_{min,max} */
>
> /*
> * Extended scheduling parameters data structure.
> @@ -21,8 +22,33 @@ struct sched_param {
> * the tasks may be useful for a wide variety of application fields, e.g.,
> * multimedia, streaming, automation and control, and many others.
> *
> - * This variant (sched_attr) is meant at describing a so-called
> - * sporadic time-constrained task. In such model a task is specified by:
> + * This variant (sched_attr) allows to define additional attributes to
> + * improve the scheduler knowledge about task requirements.
> + *
> + * Scheduling Class Attributes
> + * ===========================
> + *
> + * A subset of sched_attr attributes specifies the
> + * scheduling policy and relative POSIX attributes:
> + *
> + * @size size of the structure, for fwd/bwd compat.
> + *
> + * @sched_policy task's scheduling policy
> + * @sched_nice task's nice value (SCHED_NORMAL/BATCH)
> + * @sched_priority task's static priority (SCHED_FIFO/RR)
> + *
> + * Certain more advanced scheduling features can be controlled by a
> + * predefined set of flags via the attribute:
> + *
> + * @sched_flags for customizing the scheduler behaviour
> + *
> + * Sporadic Time-Constrained Task Attributes
> + * =========================================
> + *
> + * A subset of sched_attr attributes allows to describe a so-called
> + * sporadic time-constrained task.
> + *
> + * In such a model a task is specified by:
> * - the activation period or minimum instance inter-arrival time;
> * - the maximum (or average, depending on the actual scheduling
> * discipline) computation time of all instances, a.k.a. runtime;
> @@ -34,14 +60,8 @@ struct sched_param {
> * than the runtime and must be completed by time instant t equal to
> * the instance activation time + the deadline.
> *
> - * This is reflected by the actual fields of the sched_attr structure:
> + * This is reflected by the following fields of the sched_attr structure:
> *
> - * @size size of the structure, for fwd/bwd compat.
> - *
> - * @sched_policy task's scheduling policy
> - * @sched_flags for customizing the scheduler behaviour
> - * @sched_nice task's nice value (SCHED_NORMAL/BATCH)
> - * @sched_priority task's static priority (SCHED_FIFO/RR)
> * @sched_deadline representative of the task's deadline
> * @sched_runtime representative of the task's runtime
> * @sched_period representative of the task's period
> @@ -53,6 +73,29 @@ struct sched_param {
> * As of now, the SCHED_DEADLINE policy (sched_dl scheduling class) is the
> * only user of this new interface. More information about the algorithm
> * available in the scheduling class file or in Documentation/.
> + *
> + * Task Utilization Attributes
> + * ===========================
> + *
> + * A subset of sched_attr attributes allows to specify the utilization
> + * expected for a task. These attributes allow to inform the scheduler about
> + * the utilization boundaries within which it should schedule the task. These
> + * boundaries are valuable hints to support scheduler decisions on both task
> + * placement and frequency selection.
> + *
> + * @sched_util_min represents the minimum utilization
> + * @sched_util_max represents the maximum utilization
> + *
> + * Utilization is a value in the range [0..SCHED_CAPACITY_SCALE]. It
> + * represents the percentage of CPU time used by a task when running at the
> + * maximum frequency on the highest capacity CPU of the system. For example, a
> + * 20% utilization task is a task running for 2ms every 10ms at maximum
> + * frequency.
> + *
> + * A task with a min utilization value bigger than 0 is more likely scheduled
> + * on a CPU with a capacity big enough to fit the specified value.
> + * A task with a max utilization value smaller than 1024 is more likely
> + * scheduled on a CPU with no more capacity than the specified value.
> */
> struct sched_attr {
> __u32 size;
> @@ -70,6 +113,11 @@ struct sched_attr {
> __u64 sched_runtime;
> __u64 sched_deadline;
> __u64 sched_period;
> +
> + /* Utilization hints */
> + __u32 sched_util_min;
> + __u32 sched_util_max;
> +
> };
>
> #endif /* _UAPI_LINUX_SCHED_TYPES_H */
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 20efb32e1a7e..68aed32e8ec7 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1020,6 +1020,50 @@ int sysctl_sched_uclamp_handler(struct ctl_table *table, int write,
> return result;
> }
>
> +static int uclamp_validate(struct task_struct *p,
> + const struct sched_attr *attr)
> +{
> + unsigned int lower_bound = p->uclamp_req[UCLAMP_MIN].value;
> + unsigned int upper_bound = p->uclamp_req[UCLAMP_MAX].value;
> +
> + if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN)
> + lower_bound = attr->sched_util_min;
> + if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX)
> + upper_bound = attr->sched_util_max;
> +
> + if (lower_bound > upper_bound)
> + return -EINVAL;
> + if (upper_bound > SCHED_CAPACITY_SCALE)
> + return -EINVAL;
> +
> + return 0;
> +}
> +
> +static void __setscheduler_uclamp(struct task_struct *p,
> + const struct sched_attr *attr)
> +{
> + if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)))
> + return;
> +
> + if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) {
> + unsigned int lower_bound = attr->sched_util_min;
> +
> + p->uclamp_req[UCLAMP_MIN].user_defined = true;
> + p->uclamp_req[UCLAMP_MIN].value = lower_bound;
> + p->uclamp_req[UCLAMP_MIN].bucket_id =
> + uclamp_bucket_id(lower_bound);
> + }
> +
> + if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX) {
> + unsigned int upper_bound = attr->sched_util_max;
> +
> + p->uclamp_req[UCLAMP_MAX].user_defined = true;
> + p->uclamp_req[UCLAMP_MAX].value = upper_bound;
> + p->uclamp_req[UCLAMP_MAX].bucket_id =
> + uclamp_bucket_id(upper_bound);
> + }
> +}
> +
> static void uclamp_fork(struct task_struct *p)
> {
> unsigned int clamp_id;
> @@ -1056,6 +1100,13 @@ static void __init init_uclamp(void)
> #else /* CONFIG_UCLAMP_TASK */
> static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p) { }
> static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p) { }
> +static inline int uclamp_validate(struct task_struct *p,
> + const struct sched_attr *attr)
> +{
> + return -ENODEV;

ENOSYS might be more appropriate?

> +}
> +static void __setscheduler_uclamp(struct task_struct *p,
> + const struct sched_attr *attr) { }
> static inline void uclamp_fork(struct task_struct *p) { }
> static inline void init_uclamp(void) { }
> #endif /* CONFIG_UCLAMP_TASK */
> @@ -4424,6 +4475,13 @@ static void __setscheduler_params(struct task_struct *p,
> static void __setscheduler(struct rq *rq, struct task_struct *p,
> const struct sched_attr *attr, bool keep_boost)
> {
> + /*
> + * If params can't change scheduling class changes aren't allowed
> + * either.
> + */
> + if (attr->sched_flags & SCHED_FLAG_KEEP_PARAMS)
> + return;
> +
> __setscheduler_params(p, attr);
>
> /*
> @@ -4561,6 +4619,13 @@ static int __sched_setscheduler(struct task_struct *p,
> return retval;
> }
>
> + /* Update task specific "requested" clamps */
> + if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP) {
> + retval = uclamp_validate(p, attr);
> + if (retval)
> + return retval;
> + }
> +
> /*
> * Make sure no PI-waiters arrive (or leave) while we are
> * changing the priority of the task:
> @@ -4590,6 +4655,8 @@ static int __sched_setscheduler(struct task_struct *p,
> goto change;
> if (dl_policy(policy) && dl_param_changed(p, attr))
> goto change;
> + if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)
> + goto change;
>
> p->sched_reset_on_fork = reset_on_fork;
> task_rq_unlock(rq, p, &rf);
> @@ -4670,7 +4737,9 @@ static int __sched_setscheduler(struct task_struct *p,
> put_prev_task(rq, p);
>
> prev_class = p->sched_class;
> +
> __setscheduler(rq, p, attr, pi);
> + __setscheduler_uclamp(p, attr);
>
> if (queued) {
> /*
> @@ -4846,6 +4915,10 @@ static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *a
> if (ret)
> return -EFAULT;
>
> + if ((attr->sched_flags & SCHED_FLAG_UTIL_CLAMP) &&
> + size < SCHED_ATTR_SIZE_VER1)
> + return -EINVAL;
> +
> /*
> * XXX: Do we want to be lenient like existing syscalls; or do we want
> * to be strict and return an error on out-of-bounds values?
> @@ -4922,10 +4995,15 @@ SYSCALL_DEFINE3(sched_setattr, pid_t, pid, struct sched_attr __user *, uattr,
> rcu_read_lock();
> retval = -ESRCH;
> p = find_process_by_pid(pid);
> - if (p != NULL)
> - retval = sched_setattr(p, &attr);
> + if (likely(p))
> + get_task_struct(p);
> rcu_read_unlock();
>
> + if (likely(p)) {
> + retval = sched_setattr(p, &attr);
> + put_task_struct(p);
> + }
> +
> return retval;
> }
>
> @@ -5076,6 +5154,11 @@ SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
> else
> attr.sched_nice = task_nice(p);
>
> +#ifdef CONFIG_UCLAMP_TASK
> + attr.sched_util_min = p->uclamp_req[UCLAMP_MIN].value;
> + attr.sched_util_max = p->uclamp_req[UCLAMP_MAX].value;
> +#endif
> +
> rcu_read_unlock();
>
> retval = sched_read_attr(uattr, &attr, size);
> --
> 2.20.1
>

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