Messages in this thread Patch in this message | | | From | Patrick Bellasi <> | Subject | [PATCH v4 04/16] sched/core: uclamp: update CPU's refcount on clamp changes | Date | Tue, 28 Aug 2018 14:53:12 +0100 |
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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 can be 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 the clamp group refcount getter to trigger a CPU refcount syncup. Such a syncup is required only by currently RUNNABLE tasks which are also referencing at least one valid clamp group.
Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Paul Turner <pjt@google.com> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Todd Kjos <tkjos@google.com> Cc: Joel Fernandes <joelaf@google.com> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Quentin Perret <quentin.perret@arm.com> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> Cc: Morten Rasmussen <morten.rasmussen@arm.com> Cc: linux-kernel@vger.kernel.org Cc: linux-pm@vger.kernel.org
--- 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+thhN0dwpKCgUzs9sg@mail.gmail.com> - rename UCLAMP_NONE into UCLAMP_NOT_VALID Other: - rabased on tip/sched/core Changes in v2: Message-ID: <20180413111900.GF4082@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 | 65 ++++++++++++++++++++++++++++++++++++++++---- kernel/sched/sched.h | 16 +++++++++++ 2 files changed, 76 insertions(+), 5 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 8f908035701f..64e5c96bfdaf 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1080,6 +1080,54 @@ 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 + * @group_id: the clamp group to update + * + * Each time the clamp value of a task group is changed, the old and new clamp + * groups have to be updated for each CPU containing a RUNNABLE task belonging + * to this tasks 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, int clamp_id, int group_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 (!task_on_rq_queued(p) && !p->on_cpu) + goto done; + if (!uclamp_task_affects(p, clamp_id)) + goto done; + + /* Release p's currently referenced clamp group */ + uclamp_cpu_put_id(p, rq, clamp_id); + + /* Get p's new clamp group */ + 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 @@ -1115,6 +1163,7 @@ static inline void uclamp_group_put(int clamp_id, int group_id) /** * uclamp_group_get: increase the reference count for a clamp group + * @p: the task which clamp value must be tracked * @clamp_id: the clamp index affected by the task * @next_group_id: the clamp group to refcount * @uc_se: the utilization clamp data for the task @@ -1125,7 +1174,8 @@ static inline void uclamp_group_put(int clamp_id, int group_id) * this new clamp value. The corresponding clamp group index will be used by * the task to reference count the clamp value on CPUs while enqueued. */ -static inline void uclamp_group_get(int clamp_id, int next_group_id, +static inline void uclamp_group_get(struct task_struct *p, + int clamp_id, int next_group_id, struct uclamp_se *uc_se, unsigned int clamp_value) { @@ -1144,6 +1194,10 @@ static inline void uclamp_group_get(int clamp_id, int next_group_id, uc_map[next_group_id].se_count += 1; raw_spin_unlock_irqrestore(&uc_map[next_group_id].se_lock, flags); + /* Update CPU's clamp group refcounts of RUNNABLE task */ + if (p) + uclamp_task_update_active(p, clamp_id, next_group_id); + /* Release the previous clamp group */ uclamp_group_put(clamp_id, prev_group_id); } @@ -1202,12 +1256,12 @@ static inline int __setscheduler_uclamp(struct task_struct *p, /* Update each required clamp group */ if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) { uc_se = &p->uclamp[UCLAMP_MIN]; - uclamp_group_get(UCLAMP_MIN, group_id[UCLAMP_MIN], + uclamp_group_get(p, UCLAMP_MIN, group_id[UCLAMP_MIN], uc_se, attr->sched_util_min); } if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX) { uc_se = &p->uclamp[UCLAMP_MAX]; - uclamp_group_get(UCLAMP_MAX, group_id[UCLAMP_MAX], + uclamp_group_get(p, UCLAMP_MAX, group_id[UCLAMP_MAX], uc_se, attr->sched_util_max); } @@ -1255,7 +1309,7 @@ static void uclamp_fork(struct task_struct *p, bool reset) } p->uclamp[clamp_id].group_id = UCLAMP_NOT_VALID; - uclamp_group_get(clamp_id, next_group_id, uc_se, + uclamp_group_get(NULL, clamp_id, next_group_id, uc_se, p->uclamp[clamp_id].value); } } @@ -1289,7 +1343,8 @@ static void __init init_uclamp(void) /* Init init_task's clamp group */ uc_se = &init_task.uclamp[clamp_id]; uc_se->group_id = UCLAMP_NOT_VALID; - uclamp_group_get(clamp_id, 0, uc_se, uclamp_none(clamp_id)); + uclamp_group_get(NULL, clamp_id, 0, uc_se, + uclamp_none(clamp_id)); } } diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 513608ae4908..25d1d218ae10 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2210,6 +2210,22 @@ static inline bool uclamp_group_active(struct uclamp_group *uc_grp, { return uc_grp[group_id].tasks > 0; } + +/** + * uclamp_task_affects: check if a task affects a utilization clamp + * @p: the task to consider + * @clamp_id: the utilization clamp to check + * + * A task affects a clamp index if: + * - it's currently enqueued on a CPU + * - it references a valid clamp group index for the specified clamp index + * + * Return: true if p currently affects the specified clamp_id + */ +static inline bool uclamp_task_affects(struct task_struct *p, int clamp_id) +{ + return (p->uclamp[clamp_id].group_id != UCLAMP_NOT_VALID); +} #endif /* CONFIG_UCLAMP_TASK */ #ifdef CONFIG_CPU_FREQ -- 2.18.0
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