On 20/05/20 15:42, Dietmar Eggemann wrote: > From: Luca Abeni <[email protected]> > > 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 <[email protected]> > Signed-off-by: Dietmar Eggemann <[email protected]> > --- > 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 fa8566517715..f2e8f5a36707 100644 > --- a/kernel/sched/deadline.c > +++ b/kernel/sched/deadline.c > @@ -1643,6 +1643,7 @@ 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) > @@ -1662,10 +1663,19 @@ 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; > + > + /* > + * Take the capacity of the CPU into account 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 14cb6a97e2d2..6ebbb1f353c4 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -317,6 +317,21 @@ static inline bool __dl_overflow(struct dl_bw *dl_b, > unsigned long cap, > cap_scale(dl_b->bw, cap) < dl_b->total_bw - old_bw + new_bw; > } > > +/* > + * 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; > +} > + > extern void init_dl_bw(struct dl_bw *dl_b); > extern int sched_dl_global_validate(void); > extern void sched_dl_do_global(void); > --
Acked-by: Juri Lelli <[email protected]>
