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ANDROID: sched: Update max cpu capacity in case of max frequency constraints

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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.

Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>*
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
( Fixed cherry-pick issues )
Signed-off-by: Quentin Perret <quentin.perret@arm.com>
Change-Id: Idaa7a16723001e222e476de34df332558e48dd13
This commit is contained in:
Dietmar Eggemann 2015-09-26 18:19:54 +01:00 committed by Quentin Perret
parent 95247bf7cc
commit 9c83d8435a
3 changed files with 42 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
kernel/sched/fair.c
View File

@ -6787,7 +6787,7 @@ static int wake_cap(struct task_struct *p, int cpu, int prev_cpu)
return 0;
min_cap = min(capacity_orig_of(prev_cpu), capacity_orig_of(cpu));
max_cap = cpu_rq(cpu)->rd->max_cpu_capacity;
max_cap = cpu_rq(cpu)->rd->max_cpu_capacity.val;
/* Minimum capacity is close to max, no need to abort wake_affine */
if (max_cap - min_cap < max_cap >> 3)
@ -8379,16 +8379,45 @@ static unsigned long scale_rt_capacity(int cpu, unsigned long max)
return scale_irq_capacity(free, irq, max);
}
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;
capacity *= arch_scale_max_freq_capacity(sd, cpu);
capacity >>= SCHED_CAPACITY_SHIFT;
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);
if (!capacity)

10
kernel/sched/sched.h
View File

@ -711,6 +711,12 @@ struct perf_domain {
struct rcu_head rcu;
};
struct max_cpu_capacity {
raw_spinlock_t lock;
unsigned long val;
int cpu;
};
/* Scheduling group status flags */
#define SG_OVERLOAD 0x1 /* More than one runnable task on a CPU. */
#define SG_OVERUTILIZED 0x2 /* One or more CPUs are over-utilized. */
@ -769,7 +775,8 @@ struct root_domain {
cpumask_var_t rto_mask;
struct cpupri cpupri;
unsigned long max_cpu_capacity;
/* Maximum cpu capacity in the system. */
struct max_cpu_capacity max_cpu_capacity;
/*
* NULL-terminated list of performance domains intersecting with the
@ -782,6 +789,7 @@ extern struct root_domain def_root_domain;
extern struct mutex sched_domains_mutex;
extern void init_defrootdomain(void);
extern void init_max_cpu_capacity(struct max_cpu_capacity *mcc);
extern int sched_init_domains(const struct cpumask *cpu_map);
extern void rq_attach_root(struct rq *rq, struct root_domain *rd);
extern void sched_get_rd(struct root_domain *rd);

15
kernel/sched/topology.c
View File

@ -524,6 +524,9 @@ static int init_rootdomain(struct root_domain *rd)
if (cpupri_init(&rd->cpupri) != 0)
goto free_cpudl;
init_max_cpu_capacity(&rd->max_cpu_capacity);
return 0;
free_cpudl:
@ -1950,7 +1953,6 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
enum s_alloc alloc_state;
struct sched_domain *sd;
struct s_data d;
struct rq *rq = NULL;
int i, ret = -ENOMEM;
struct sched_domain_topology_level *tl_asym;
bool has_asym = false;
@ -2013,13 +2015,7 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
/* Attach the domains */
rcu_read_lock();
for_each_cpu(i, cpu_map) {
rq = cpu_rq(i);
sd = *per_cpu_ptr(d.sd, i);
/* Use READ_ONCE()/WRITE_ONCE() to avoid load/store tearing: */
if (rq->cpu_capacity_orig > READ_ONCE(d.rd->max_cpu_capacity))
WRITE_ONCE(d.rd->max_cpu_capacity, rq->cpu_capacity_orig);
cpu_attach_domain(sd, d.rd, i);
}
rcu_read_unlock();
@ -2027,11 +2023,6 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
if (has_asym)
static_branch_enable_cpuslocked(&sched_asym_cpucapacity);
if (rq && sched_debug_enabled) {
pr_info("root domain span: %*pbl (max cpu_capacity = %lu)\n",
cpumask_pr_args(cpu_map), rq->rd->max_cpu_capacity);
}
ret = 0;
error:
__free_domain_allocs(&d, alloc_state, cpu_map);