Messages in this thread Patch in this message | | | From | Dietmar Eggemann <> | Subject | [PATCH 3/4] sched/deadline: Make DL capacity-aware | Date | Wed, 8 Apr 2020 11:50:11 +0200 |
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From: Luca Abeni <luca.abeni@santannapisa.it>
The current SCHED_DEADLINE (DL) scheduler uses a global EDF scheduling algorithm w/o considering CPU capacity or task utilization. This works well on homogeneous systems where DL tasks are guaranteed to have a bounded tardiness but presents issues on heterogeneous systems.
A DL task can migrate to a CPU which does not have enough CPU capacity to correctly serve the task (e.g. a task w/ 70ms runtime and 100ms period on a CPU w/ 512 capacity).
Add the DL fitness function dl_task_fits_capacity() for DL admission control on heterogeneous systems. A task fits onto a CPU if:
CPU original capacity / 1024 >= task runtime / task deadline
Use this function on heterogeneous systems to try to find a CPU which meets this criterion during task wakeup, push and offline migration.
On homogeneous systems the original behavior of the DL admission control should be retained.
Signed-off-by: Luca Abeni <luca.abeni@santannapisa.it> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com> --- kernel/sched/cpudeadline.c | 14 +++++++++++++- kernel/sched/deadline.c | 18 ++++++++++++++---- kernel/sched/sched.h | 15 +++++++++++++++ 3 files changed, 42 insertions(+), 5 deletions(-)
diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c index 5cc4012572ec..8630f2a40a3f 100644 --- a/kernel/sched/cpudeadline.c +++ b/kernel/sched/cpudeadline.c @@ -121,7 +121,19 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p, if (later_mask && cpumask_and(later_mask, cp->free_cpus, p->cpus_ptr)) { - return 1; + int cpu; + + if (!static_branch_unlikely(&sched_asym_cpucapacity)) + return 1; + + /* Ensure the capacity of the CPUs fits the task. */ + for_each_cpu(cpu, later_mask) { + if (!dl_task_fits_capacity(p, cpu)) + cpumask_clear_cpu(cpu, later_mask); + } + + if (!cpumask_empty(later_mask)) + return 1; } else { int best_cpu = cpudl_maximum(cp); diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 53b34a95e29e..e10adf1e3c27 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -1604,6 +1604,7 @@ static int select_task_rq_dl(struct task_struct *p, int cpu, int sd_flag, int flags) { struct task_struct *curr; + bool select_rq; struct rq *rq; if (sd_flag != SD_BALANCE_WAKE) @@ -1623,10 +1624,19 @@ select_task_rq_dl(struct task_struct *p, int cpu, int sd_flag, int flags) * other hand, if it has a shorter deadline, we * try to make it stay here, it might be important. */ - if (unlikely(dl_task(curr)) && - (curr->nr_cpus_allowed < 2 || - !dl_entity_preempt(&p->dl, &curr->dl)) && - (p->nr_cpus_allowed > 1)) { + select_rq = unlikely(dl_task(curr)) && + (curr->nr_cpus_allowed < 2 || + !dl_entity_preempt(&p->dl, &curr->dl)) && + p->nr_cpus_allowed > 1; + + /* + * We take into account the capacity of the CPU to + * ensure it fits the requirement of the task. + */ + if (static_branch_unlikely(&sched_asym_cpucapacity)) + select_rq |= !dl_task_fits_capacity(p, cpu); + + if (select_rq) { int target = find_later_rq(p); if (target != -1 && diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 6cbdf7a342a6..598b58c68639 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -306,6 +306,21 @@ void __dl_add(struct dl_bw *dl_b, u64 tsk_bw, int cpus) static inline unsigned long rd_capacity(int cpu); +/* + * Verify the fitness of task @p to run on @cpu taking into account the + * CPU original capacity and the runtime/deadline ratio of the task. + * + * The function will return true if the CPU original capacity of the + * @cpu scaled by SCHED_CAPACITY_SCALE >= runtime/deadline ratio of the + * task and false otherwise. + */ +static inline bool dl_task_fits_capacity(struct task_struct *p, int cpu) +{ + unsigned long cap = arch_scale_cpu_capacity(cpu); + + return cap_scale(p->dl.dl_deadline, cap) >= p->dl.dl_runtime; +} + static inline bool __dl_overflow(struct dl_bw *dl_b, int cpu, u64 old_bw, u64 new_bw) { -- 2.17.1
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