When a task's util_clamp value is configured via sched_setattr(2), this value has to be properly accounted in the corresponding clamp group every time the task is enqueued and dequeued. When cgroups are also in use, per-task clamp values have to be aggregated to those of the CPU's controller's Task Group (TG) in which the task is currently living.
Let's update uclamp_cpu_get() to provide aggregation between the task and the TG clamp values. Every time a task is enqueued, it will be accounted in the clamp_group which defines the smaller clamp between the task specific value and its TG effective value. This also mimics what already happen for a task's CPU affinity mask when the task is also living in a cpuset. The overall idea is that cgroup attributes are always used to restrict the per-task attributes. Thus, this implementation allows to: 1. ensure cgroup clamps are always used to restrict task specific requests, i.e. boosted only up to the effective granted value or clamped at least to a certain value 2. implements a "nice-like" policy, where tasks are still allowed to request less then what enforced by their current TG For this mecanisms to work properly, we add the concept of "active" clamp group, which is used to track the currently most restrictive clamp value each task is subject to. The active clamp is computed at enqueue time, by using an additional task_struct::uclamp_group_id to keep track of the clamp group in which each task is currently accounted into. This allows to update task constrains on demand, only when a task becames RUNNABLE, thus always using the most restrictive clamp depending on the current TG's settings. This solution allows also to better decouple the slow-path, where task and task group clamp values are updated, from the fast-path, where the most appropriate clamp value is tracked by refcounting clamp groups. For consistency purposes, as well as to properly inform userspace, the sched_getattr(2) call is updated to always return the properly aggregated constrains as described above. This will also make sched_getattr(2) a convenient userpace API to know the utilization constraints enforced on a task by the cgroup's CPU controller. Signed-off-by: Patrick Bellasi <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Tejun Heo <[email protected]> Cc: Paul Turner <[email protected]> Cc: Suren Baghdasaryan <[email protected]> Cc: Todd Kjos <[email protected]> Cc: Joel Fernandes <[email protected]> Cc: Steve Muckle <[email protected]> Cc: Juri Lelli <[email protected]> Cc: Dietmar Eggemann <[email protected]> Cc: Morten Rasmussen <[email protected]> Cc: [email protected] Cc: [email protected] --- Changes in v3: Message-ID: <CAJuCfpFnj2g3+ZpR4fP4yqfxs0zd=c-zehr2xm7m_c+wdl9...@mail.gmail.com> - rename UCLAMP_NONE into UCLAMP_NOT_VALID - fix not required override - fix typos in changelog Others: - clean up uclamp_cpu_get_id()/sched_getattr() code by moving task's clamp group_id/value code into dedicated getter functions: uclamp_task_group_id(), uclamp_group_value() and uclamp_task_value() - rebased on tip/sched/core Changes in v2: OSPM discussion: - implement a "nice" semantics where cgroup clamp values are always used to restrict task specific clamp values, i.e. tasks running on a TG are only allowed to demote themself. Other: - rabased on v4.18-rc4 - this code has been split from a previous patch to simplify the review --- include/linux/sched.h | 2 ++ kernel/sched/core.c | 78 ++++++++++++++++++++++++++++++++++++++----- kernel/sched/sched.h | 2 +- 3 files changed, 73 insertions(+), 9 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 04f3b47a31bc..753d10cd25f1 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -681,6 +681,8 @@ struct task_struct { struct sched_dl_entity dl; #ifdef CONFIG_UCLAMP_TASK + /* Clamp group the task is currently accounted into */ + int uclamp_group_id[UCLAMP_CNT]; /* Utlization clamp values for this task */ struct uclamp_se uclamp[UCLAMP_CNT]; #endif diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 01229864fd93..f54fd9bda9a7 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -941,14 +941,65 @@ static inline void uclamp_cpu_update(struct rq *rq, int clamp_id, rq->uclamp.value[clamp_id] = max_value; } +static inline int uclamp_task_group_id(struct task_struct *p, int clamp_id) +{ + struct uclamp_se *uc_se; + int clamp_value; + int group_id; + + /* Taks currently accounted into a clamp group */ + if (uclamp_task_affects(p, clamp_id)) + return p->uclamp_group_id[clamp_id]; + + /* Task specific clamp value */ + uc_se = &p->uclamp[clamp_id]; + clamp_value = uc_se->value; + group_id = uc_se->group_id; + +#ifdef CONFIG_UCLAMP_TASK_GROUP + /* Use TG's clamp value to limit task specific values */ + uc_se = &task_group(p)->uclamp[clamp_id]; + if (group_id == UCLAMP_NOT_VALID || + clamp_value > uc_se->effective.value) { + group_id = uc_se->effective.group_id; + } +#endif + + return group_id; +} + +static inline int uclamp_group_value(int clamp_id, int group_id) +{ + struct uclamp_map *uc_map = &uclamp_maps[clamp_id][0]; + + if (group_id == UCLAMP_NOT_VALID) + return uclamp_none(clamp_id); + + return uc_map[group_id].value; +} + +static inline int uclamp_task_value(struct task_struct *p, int clamp_id) +{ + int group_id = uclamp_task_group_id(p, clamp_id); + + return uclamp_group_value(clamp_id, group_id); +} + /** * uclamp_cpu_get_id(): increase reference count for a clamp group on a CPU * @p: the task being enqueued on a CPU * @rq: the CPU's rq where the clamp group has to be reference counted * @clamp_id: the utilization clamp (e.g. min or max utilization) to reference * - * Once a task is enqueued on a CPU's RQ, the clamp group currently defined by - * the task's uclamp.group_id is reference counted on that CPU. + * Once a task is enqueued on a CPU's RQ, the most restrictive clamp group, + * among the task specific and that of the task's cgroup one, is reference + * counted on that CPU. + * + * Since the CPUs reference counted clamp group can be either that of the task + * or of its cgroup, we keep track of the reference counted clamp group by + * storing its index (group_id) into the task's task_struct::uclamp_group_id. + * This group index will then be used at task's dequeue time to release the + * correct refcount. */ static inline void uclamp_cpu_get_id(struct task_struct *p, struct rq *rq, int clamp_id) @@ -959,17 +1010,20 @@ static inline void uclamp_cpu_get_id(struct task_struct *p, int group_id; /* No task specific clamp values: nothing to do */ - group_id = p->uclamp[clamp_id].group_id; + group_id = uclamp_task_group_id(p, clamp_id); if (group_id == UCLAMP_NOT_VALID) return; + clamp_value = uclamp_group_value(clamp_id, group_id); /* Reference count the task into its current group_id */ uc_grp = &rq->uclamp.group[clamp_id][0]; uc_grp[group_id].tasks += 1; + /* Track the effective clamp group */ + p->uclamp_group_id[clamp_id] = group_id; + /* Force clamp update on idle exit */ uc_cpu = &rq->uclamp; - clamp_value = p->uclamp[clamp_id].value; if (unlikely(uc_cpu->flags & UCLAMP_FLAG_IDLE)) { /* * This function is called for both UCLAMP_MIN (before) and @@ -1012,7 +1066,7 @@ static inline void uclamp_cpu_put_id(struct task_struct *p, int group_id; /* No task specific clamp values: nothing to do */ - group_id = p->uclamp[clamp_id].group_id; + group_id = p->uclamp_group_id[clamp_id]; if (group_id == UCLAMP_NOT_VALID) return; @@ -1027,6 +1081,9 @@ static inline void uclamp_cpu_put_id(struct task_struct *p, #endif uc_grp[group_id].tasks -= 1; + /* Flag the task as not affecting any clamp index */ + p->uclamp_group_id[clamp_id] = UCLAMP_NOT_VALID; + /* If this is not the last task, no updates are required */ if (uc_grp[group_id].tasks > 0) return; @@ -2885,6 +2942,8 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p) #endif #ifdef CONFIG_UCLAMP_TASK + memset(&p->uclamp_group_id, UCLAMP_NOT_VALID, + sizeof(p->uclamp_group_id)); p->uclamp[UCLAMP_MIN].value = 0; p->uclamp[UCLAMP_MIN].group_id = UCLAMP_NOT_VALID; p->uclamp[UCLAMP_MAX].value = SCHED_CAPACITY_SCALE; @@ -5467,8 +5526,8 @@ SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr, attr.sched_nice = task_nice(p); #ifdef CONFIG_UCLAMP_TASK - attr.sched_util_min = p->uclamp[UCLAMP_MIN].value; - attr.sched_util_max = p->uclamp[UCLAMP_MAX].value; + attr.sched_util_min = uclamp_task_value(p, UCLAMP_MIN); + attr.sched_util_max = uclamp_task_value(p, UCLAMP_MAX); #endif rcu_read_unlock(); @@ -7285,8 +7344,11 @@ static void cpu_util_update_hier(struct cgroup_subsys_state *css, * groups we consider their current value. */ uc_se = &css_tg(css)->uclamp[clamp_id]; - if (css != top_css) + if (css != top_css) { value = uc_se->value; + group_id = uc_se->effective.group_id; + } + /* * Skip the whole subtrees if the current effective clamp is * alredy matching the TG's clamp value. diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index a443b2c22cb7..a296b6463f1e 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2229,7 +2229,7 @@ static inline bool uclamp_group_active(struct uclamp_group *uc_grp, */ static inline bool uclamp_task_affects(struct task_struct *p, int clamp_id) { - return (p->uclamp[clamp_id].group_id != UCLAMP_NOT_VALID); + return (p->uclamp_group_id[clamp_id] != UCLAMP_NOT_VALID); } /** -- 2.18.0
