On 20/05/20 15:42, Dietmar Eggemann wrote: > From: Luca Abeni <[email protected]> > > The current SCHED_DEADLINE (DL) admission control ensures that > > sum of reserved CPU bandwidth < x * M > > where > > x = /proc/sys/kernel/sched_rt_{runtime,period}_us > M = # CPUs in root domain. > > DL admission control works well for homogeneous systems where the > capacity of all CPUs are equal (1024). I.e. bounded tardiness for DL > and non-starvation of non-DL tasks is guaranteed. > > But on heterogeneous systems where capacity of CPUs are different it > could fail by over-allocating CPU time on smaller capacity CPUs. > > On an Arm big.LITTLE/DynamIQ system DL tasks can easily starve other > tasks making it unusable. > > Fix this by explicitly considering the CPU capacity in the DL admission > test by replacing M with the root domain CPU capacity sum. > > Signed-off-by: Luca Abeni <[email protected]> > Signed-off-by: Dietmar Eggemann <[email protected]> > --- > kernel/sched/deadline.c | 30 +++++++++++++++++------------- > kernel/sched/sched.h | 6 +++--- > 2 files changed, 20 insertions(+), 16 deletions(-) > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c > index ea7282ce484c..fa8566517715 100644 > --- a/kernel/sched/deadline.c > +++ b/kernel/sched/deadline.c > @@ -2590,11 +2590,12 @@ void sched_dl_do_global(void) > int sched_dl_overflow(struct task_struct *p, int policy, > const struct sched_attr *attr) > { > - struct dl_bw *dl_b = dl_bw_of(task_cpu(p)); > u64 period = attr->sched_period ?: attr->sched_deadline; > u64 runtime = attr->sched_runtime; > u64 new_bw = dl_policy(policy) ? to_ratio(period, runtime) : 0; > - int cpus, err = -1; > + int cpus, err = -1, cpu = task_cpu(p); > + struct dl_bw *dl_b = dl_bw_of(cpu); > + unsigned long cap; > > if (attr->sched_flags & SCHED_FLAG_SUGOV) > return 0; > @@ -2609,15 +2610,17 @@ int sched_dl_overflow(struct task_struct *p, int > policy, > * allocated bandwidth of the container. > */ > raw_spin_lock(&dl_b->lock); > - cpus = dl_bw_cpus(task_cpu(p)); > + cpus = dl_bw_cpus(cpu); > + cap = dl_bw_capacity(cpu); > + > if (dl_policy(policy) && !task_has_dl_policy(p) && > - !__dl_overflow(dl_b, cpus, 0, new_bw)) { > + !__dl_overflow(dl_b, cap, 0, new_bw)) { > if (hrtimer_active(&p->dl.inactive_timer)) > __dl_sub(dl_b, p->dl.dl_bw, cpus); > __dl_add(dl_b, new_bw, cpus); > err = 0; > } else if (dl_policy(policy) && task_has_dl_policy(p) && > - !__dl_overflow(dl_b, cpus, p->dl.dl_bw, new_bw)) { > + !__dl_overflow(dl_b, cap, p->dl.dl_bw, new_bw)) { > /* > * XXX this is slightly incorrect: when the task > * utilization decreases, we should delay the total > @@ -2753,19 +2756,19 @@ bool dl_param_changed(struct task_struct *p, const > struct sched_attr *attr) > #ifdef CONFIG_SMP > int dl_task_can_attach(struct task_struct *p, const struct cpumask > *cs_cpus_allowed) > { > + unsigned long flags, cap; > unsigned int dest_cpu; > struct dl_bw *dl_b; > bool overflow; > - int cpus, ret; > - unsigned long flags; > + int ret; > > dest_cpu = cpumask_any_and(cpu_active_mask, cs_cpus_allowed); > > rcu_read_lock_sched(); > dl_b = dl_bw_of(dest_cpu); > raw_spin_lock_irqsave(&dl_b->lock, flags); > - cpus = dl_bw_cpus(dest_cpu); > - overflow = __dl_overflow(dl_b, cpus, 0, p->dl.dl_bw); > + cap = dl_bw_capacity(dest_cpu); > + overflow = __dl_overflow(dl_b, cap, 0, p->dl.dl_bw); > if (overflow) { > ret = -EBUSY; > } else { > @@ -2775,6 +2778,8 @@ int dl_task_can_attach(struct task_struct *p, const > struct cpumask *cs_cpus_allo > * We will free resources in the source root_domain > * later on (see set_cpus_allowed_dl()). > */ > + int cpus = dl_bw_cpus(dest_cpu); > + > __dl_add(dl_b, p->dl.dl_bw, cpus); > ret = 0; > } > @@ -2807,16 +2812,15 @@ int dl_cpuset_cpumask_can_shrink(const struct cpumask > *cur, > > bool dl_cpu_busy(unsigned int cpu) > { > - unsigned long flags; > + unsigned long flags, cap; > struct dl_bw *dl_b; > bool overflow; > - int cpus; > > rcu_read_lock_sched(); > dl_b = dl_bw_of(cpu); > raw_spin_lock_irqsave(&dl_b->lock, flags); > - cpus = dl_bw_cpus(cpu); > - overflow = __dl_overflow(dl_b, cpus, 0, 0); > + cap = dl_bw_capacity(cpu); > + overflow = __dl_overflow(dl_b, cap, 0, 0); > raw_spin_unlock_irqrestore(&dl_b->lock, flags); > rcu_read_unlock_sched(); > > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index 21416b30c520..14cb6a97e2d2 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -310,11 +310,11 @@ void __dl_add(struct dl_bw *dl_b, u64 tsk_bw, int cpus) > __dl_update(dl_b, -((s32)tsk_bw / cpus)); > } > > -static inline > -bool __dl_overflow(struct dl_bw *dl_b, int cpus, u64 old_bw, u64 new_bw) > +static inline bool __dl_overflow(struct dl_bw *dl_b, unsigned long cap, > + u64 old_bw, u64 new_bw) > { > return dl_b->bw != -1 && > - dl_b->bw * cpus < dl_b->total_bw - old_bw + new_bw; > + cap_scale(dl_b->bw, cap) < dl_b->total_bw - old_bw + new_bw; > } > > extern void init_dl_bw(struct dl_bw *dl_b); > --
Acked-by: Juri Lelli <[email protected]>
