iMX/i2som-imx-linux
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

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

Browse Source 
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: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>
Change-Id: Idaa7a16723001e222e476de34df332558e48dd13
This commit is contained in:
Dietmar Eggemann
2015-09-26 18:19:54 +01:00
committed by Ionela Voinescu
parent d0df20f98c
commit 2cc3df5e1c
3 changed files with 42 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files

32
kernel/sched/fair.c
View File

@ -7236,7 +7236,7 @@ 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)
@ -8834,16 +8834,46 @@ 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;
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 >>= SCHED_CAPACITY_SHIFT;

10
kernel/sched/sched.h
View File

@ -612,6 +612,12 @@ static inline bool sched_asym_prefer(int a, int b)
return arch_asym_cpu_priority(a) > arch_asym_cpu_priority(b);
}
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
@ -663,7 +669,8 @@ 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;
/* First cpu with maximum and minimum original capacity */
int max_cap_orig_cpu, min_cap_orig_cpu;
@ -673,6 +680,7 @@ 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);

13
kernel/sched/topology.c
View File

@ -304,6 +304,8 @@ static int init_rootdomain(struct root_domain *rd)
rd->max_cap_orig_cpu = rd->min_cap_orig_cpu = -1;
init_max_cpu_capacity(&rd->max_cpu_capacity);
return 0;
free_cpudl:
@ -1818,7 +1820,6 @@ 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;
alloc_state = __visit_domain_allocation_hell(&d, cpu_map);
@ -1873,13 +1874,8 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
int max_cpu = READ_ONCE(d.rd->max_cap_orig_cpu);
int min_cpu = READ_ONCE(d.rd->min_cap_orig_cpu);
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);
if ((max_cpu < 0) || (cpu_rq(i)->cpu_capacity_orig >
cpu_rq(max_cpu)->cpu_capacity_orig))
WRITE_ONCE(d.rd->max_cap_orig_cpu, i);
@ -1895,11 +1891,6 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att
if (!cpumask_empty(cpu_map))
update_asym_cpucapacity(cpumask_first(cpu_map));
if (rq && sched_debug_enabled) {
pr_info("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);