From 05a773bfc98b786cf504af1bce8bfe4a84a6a586 Mon Sep 17 00:00:00 2001 From: Dietmar Eggemann Date: Sat, 26 Sep 2015 18:19:54 +0100 Subject: [PATCH] sched: Update max cpu capacity in case of max frequency constraints Wakeup balancing uses cpu capacity awareness and needs to know the system-wide maximum cpu capacity. Patch "sched: Store system-wide maximum cpu capacity in root domain" finds the system-wide maximum cpu capacity during scheduler domain hierarchy setup. This is sufficient as long as maximum frequency invariance is not enabled. If it is enabled, the system-wide maximum cpu capacity can change between scheduler domain hierarchy setups due to frequency capping. The cpu capacity is changed in update_cpu_capacity() which is called in load balance on the lowest scheduler domain hierarchy level. To be able to know if a change in cpu capacity for a certain cpu also has an effect on the system-wide maximum cpu capacity it is normally necessary to iterate over all cpus. This would be way too costly. That's why this patch follows a different approach. The unsigned long max_cpu_capacity value in struct root_domain is replaced with a struct max_cpu_capacity, containing value (the max_cpu_capacity) and cpu (the cpu index of the cpu providing the maximum cpu_capacity). Changes to the system-wide maximum cpu capacity and the cpu index are made if: 1 System-wide maximum cpu capacity < cpu capacity 2 System-wide maximum cpu capacity > cpu capacity and cpu index == cpu There are no changes to the system-wide maximum cpu capacity in all other cases. Atomic read and write access to the pair (max_cpu_capacity.val, max_cpu_capacity.cpu) is enforced by max_cpu_capacity.lock. The access to max_cpu_capacity.val in task_fits_max() is still performed without taking the max_cpu_capacity.lock. The code to set max cpu capacity in build_sched_domains() has been removed because the whole functionality is now provided by update_cpu_capacity() instead. This approach can introduce errors temporarily, e.g. in case the cpu currently providing the max cpu capacity has its cpu capacity lowered due to frequency capping and calls update_cpu_capacity() before any cpu which might provide the max cpu now. There is also an outstanding question: Should the cpu capacity of a cpu going idle be set to a very small value? Signed-off-by: Dietmar Eggemann --- kernel/sched/core.c | 8 ++------ kernel/sched/fair.c | 32 +++++++++++++++++++++++++++++++- kernel/sched/sched.h | 10 +++++++++- 3 files changed, 42 insertions(+), 8 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index bc5bb26ccf3b..3680e76b6beb 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5888,6 +5888,8 @@ static int init_rootdomain(struct root_domain *rd) if (cpupri_init(&rd->cpupri) != 0) goto free_rto_mask; + + init_max_cpu_capacity(&rd->max_cpu_capacity); return 0; free_rto_mask: @@ -7105,15 +7107,9 @@ static int build_sched_domains(const struct cpumask *cpu_map, rq = cpu_rq(i); sd = *per_cpu_ptr(d.sd, i); cpu_attach_domain(sd, d.rd, i); - - if (rq->cpu_capacity_orig > rq->rd->max_cpu_capacity) - rq->rd->max_cpu_capacity = rq->cpu_capacity_orig; } rcu_read_unlock(); - if (rq) - pr_info("max cpu_capacity %lu\n", rq->rd->max_cpu_capacity); - ret = 0; error: __free_domain_allocs(&d, alloc_state, cpu_map); diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 7327221c991e..91dfc8aa8aff 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5078,7 +5078,7 @@ static inline bool __task_fits(struct task_struct *p, int cpu, int util) static inline bool task_fits_max(struct task_struct *p, int cpu) { unsigned long capacity = capacity_of(cpu); - unsigned long max_capacity = cpu_rq(cpu)->rd->max_cpu_capacity; + unsigned long max_capacity = cpu_rq(cpu)->rd->max_cpu_capacity.val; if (capacity == max_capacity) return true; @@ -6564,13 +6564,43 @@ static unsigned long scale_rt_capacity(int cpu) return 1; } +void init_max_cpu_capacity(struct max_cpu_capacity *mcc) +{ + raw_spin_lock_init(&mcc->lock); + mcc->val = 0; + mcc->cpu = -1; +} + static void update_cpu_capacity(struct sched_domain *sd, int cpu) { unsigned long capacity = arch_scale_cpu_capacity(sd, cpu); struct sched_group *sdg = sd->groups; + struct max_cpu_capacity *mcc; + unsigned long max_capacity; + int max_cap_cpu; + unsigned long flags; cpu_rq(cpu)->cpu_capacity_orig = capacity; + mcc = &cpu_rq(cpu)->rd->max_cpu_capacity; + + raw_spin_lock_irqsave(&mcc->lock, flags); + max_capacity = mcc->val; + max_cap_cpu = mcc->cpu; + + if ((max_capacity > capacity && max_cap_cpu == cpu) || + (max_capacity < capacity)) { + mcc->val = capacity; + mcc->cpu = cpu; +#ifdef CONFIG_SCHED_DEBUG + raw_spin_unlock_irqrestore(&mcc->lock, flags); + pr_info("CPU%d: update max cpu_capacity %lu\n", cpu, capacity); + goto skip_unlock; +#endif + } + raw_spin_unlock_irqrestore(&mcc->lock, flags); + +skip_unlock: __attribute__ ((unused)); capacity *= scale_rt_capacity(cpu); capacity >>= SCHED_CAPACITY_SHIFT; diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 2301b0476b90..aac581932eff 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -510,6 +510,12 @@ struct dl_rq { #ifdef CONFIG_SMP +struct max_cpu_capacity { + raw_spinlock_t lock; + unsigned long val; + int cpu; +}; + /* * We add the notion of a root-domain which will be used to define per-domain * variables. Each exclusive cpuset essentially defines an island domain by @@ -548,7 +554,7 @@ struct root_domain { struct cpupri cpupri; /* Maximum cpu capacity in the system. */ - unsigned long max_cpu_capacity; + struct max_cpu_capacity max_cpu_capacity; }; extern struct root_domain def_root_domain; @@ -1340,6 +1346,8 @@ unsigned long to_ratio(u64 period, u64 runtime); extern void init_entity_runnable_average(struct sched_entity *se); +extern void init_max_cpu_capacity(struct max_cpu_capacity *mcc); + static inline void add_nr_running(struct rq *rq, unsigned count) { unsigned prev_nr = rq->nr_running; -- 2.20.1