Utilization clamp values enforced on a CPU by a task can be updated at run-time, for example via a sched_setattr syscall, while a task is currently RUNNABLE on that CPU. In these cases, the task is already refcounting a clamp group for its CPU and thus we need to update this reference to ensure the new constraints are immediately enforced.
Since a clamp value change always implies a clamp group refcount update, this patch hooks into uclamp_group_get() to trigger a CPU refcount syncup, via uclamp_cpu_{put,get}_id(), whenever a task is RUNNABLE. Signed-off-by: Patrick Bellasi <patrick.bell...@arm.com> Cc: Ingo Molnar <mi...@redhat.com> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Paul Turner <p...@google.com> Cc: Suren Baghdasaryan <sur...@google.com> Cc: Todd Kjos <tk...@google.com> Cc: Joel Fernandes <joe...@google.com> Cc: Juri Lelli <juri.le...@redhat.com> Cc: Quentin Perret <quentin.per...@arm.com> Cc: Dietmar Eggemann <dietmar.eggem...@arm.com> Cc: Morten Rasmussen <morten.rasmus...@arm.com> Cc: linux-kernel@vger.kernel.org Cc: linux...@vger.kernel.org --- Changes in v5: Message-ID: <20180914134128.GP1413@e110439-lin> - remove not required uclamp_task_affects() since now all tasks always have a valid clamp group assigned Others: - consistently use "unsigned int" for both clamp_id and group_id - fixup documentation - reduced usage of inline comments - rebased on v4.19 Changes in v4: Message-ID: <20180816132249.GA2960@e110439-lin> - inline uclamp_task_active() code into uclamp_task_update_active() - get rid of the now unused uclamp_task_active() Other: - allow to call uclamp_group_get() without a task pointer, which is used to refcount the initial clamp group for all the global objects (init_task, root_task_group and system_defaults) - rebased on v4.19-rc1 Changes in v3: Message-ID: <CAJuCfpF6=L=0lrmnnjrtnpazt4dwkqnv+thhn0dwpkcguzs...@mail.gmail.com> - rename UCLAMP_NONE into UCLAMP_NOT_VALID Other: - rabased on tip/sched/core Changes in v2: Message-ID: <20180413111900.gf4...@hirez.programming.kicks-ass.net> - get rid of the group_id back annotation which is not requires at this stage where we have only per-task clamping support. It will be introduce later when CGroups support is added. Other: - rabased on v4.18-rc4 - this code has been split from a previous patch to simplify the review --- kernel/sched/core.c | 60 ++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 54 insertions(+), 6 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index a98a96a7d9f1..21f6251a1d44 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -936,6 +936,48 @@ static inline void uclamp_cpu_put(struct rq *rq, struct task_struct *p) uclamp_cpu_put_id(p, rq, clamp_id); } +/** + * uclamp_task_update_active: update the clamp group of a RUNNABLE task + * @p: the task which clamp groups must be updated + * @clamp_id: the clamp index to consider + * + * Each time the clamp value of a task group is changed, the old and new clamp + * groups must be updated for each CPU containing a RUNNABLE task belonging to + * that task group. Sleeping tasks are not updated since they will be enqueued + * with the proper clamp group index at their next activation. + */ +static inline void +uclamp_task_update_active(struct task_struct *p, unsigned int clamp_id) +{ + struct rq_flags rf; + struct rq *rq; + + /* + * Lock the task and the CPU where the task is (or was) queued. + * + * We might lock the (previous) rq of a !RUNNABLE task, but that's the + * price to pay to safely serialize util_{min,max} updates with + * enqueues, dequeues and migration operations. + * This is the same locking schema used by __set_cpus_allowed_ptr(). + */ + rq = task_rq_lock(p, &rf); + + /* + * The setting of the clamp group is serialized by task_rq_lock(). + * Thus, if the task is not yet RUNNABLE and its task_struct is not + * affecting a valid clamp group, then the next time it's going to be + * enqueued it will already see the updated clamp group value. + */ + if (!p->uclamp[clamp_id].active) + goto done; + + uclamp_cpu_put_id(p, rq, clamp_id); + uclamp_cpu_get_id(p, rq, clamp_id); + +done: + task_rq_unlock(rq, p, &rf); +} + /** * uclamp_group_put: decrease the reference count for a clamp group * @clamp_id: the clamp index which was affected by a task group @@ -970,6 +1012,7 @@ static void uclamp_group_put(unsigned int clamp_id, unsigned int group_id) /** * uclamp_group_get: increase the reference count for a clamp group + * @p: the task which clamp value must be tracked * @uc_se: the utilization clamp data for the task * @clamp_id: the clamp index affected by the task * @clamp_value: the new clamp value for the task @@ -980,8 +1023,8 @@ static void uclamp_group_put(unsigned int clamp_id, unsigned int group_id) * reference count the corresponding clamp value while the task is enqueued on * a CPU. */ -static void uclamp_group_get(struct uclamp_se *uc_se, unsigned int clamp_id, - unsigned int clamp_value) +static void uclamp_group_get(struct task_struct *p, struct uclamp_se *uc_se, + unsigned int clamp_id, unsigned int clamp_value) { union uclamp_map *uc_maps = &uclamp_maps[clamp_id][0]; unsigned int prev_group_id = uc_se->group_id; @@ -1046,6 +1089,10 @@ static void uclamp_group_get(struct uclamp_se *uc_se, unsigned int clamp_id, uc_se->value = clamp_value; uc_se->group_id = group_id; + /* Update CPU's clamp group refcounts of RUNNABLE task */ + if (p) + uclamp_task_update_active(p, clamp_id); + /* Release the previous clamp group */ if (uc_se->mapped) uclamp_group_put(clamp_id, prev_group_id); @@ -1073,11 +1120,11 @@ static int __setscheduler_uclamp(struct task_struct *p, /* Update each required clamp group */ if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) { - uclamp_group_get(&p->uclamp[UCLAMP_MIN], + uclamp_group_get(p, &p->uclamp[UCLAMP_MIN], UCLAMP_MIN, lower_bound); } if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX) { - uclamp_group_get(&p->uclamp[UCLAMP_MAX], + uclamp_group_get(p, &p->uclamp[UCLAMP_MAX], UCLAMP_MAX, upper_bound); } @@ -1125,7 +1172,8 @@ static void uclamp_fork(struct task_struct *p, bool reset) p->uclamp[clamp_id].mapped = false; p->uclamp[clamp_id].active = false; - uclamp_group_get(&p->uclamp[clamp_id], clamp_id, clamp_value); + uclamp_group_get(NULL, &p->uclamp[clamp_id], + clamp_id, clamp_value); } } @@ -1146,7 +1194,7 @@ static void __init init_uclamp(void) memset(uclamp_maps, 0, sizeof(uclamp_maps)); for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id) { uc_se = &init_task.uclamp[clamp_id]; - uclamp_group_get(uc_se, clamp_id, uclamp_none(clamp_id)); + uclamp_group_get(NULL, uc_se, clamp_id, uclamp_none(clamp_id)); } } -- 2.18.0