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sched: Remove unnecessary iteration over sched domains to update nr_busy_cpus

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nr_busy_cpus parameter is used by nohz_kick_needed() to find out the
number of busy cpus in a sched domain which has SD_SHARE_PKG_RESOURCES
flag set.  Therefore instead of updating nr_busy_cpus at every level
of sched domain, since it is irrelevant, we can update this parameter
only at the parent domain of the sd which has this flag set. Introduce
a per-cpu parameter sd_busy which represents this parent domain.

In nohz_kick_needed() we directly query the nr_busy_cpus parameter
associated with the groups of sd_busy.

By associating sd_busy with the highest domain which has
SD_SHARE_PKG_RESOURCES flag set, we cover all lower level domains
which could have this flag set and trigger nohz_idle_balancing if any
of the levels have more than one busy cpu.

sd_busy is irrelevant for asymmetric load balancing. However sd_asym
has been introduced to represent the highest sched domain which has
SD_ASYM_PACKING flag set so that it can be queried directly when
required.

While we are at it, we might as well change the nohz_idle parameter to
be updated at the sd_busy domain level alone and not the base domain
level of a CPU.  This will unify the concept of busy cpus at just one
level of sched domain where it is currently used.

Signed-off-by: Preeti U Murthy<preeti@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: svaidy@linux.vnet.ibm.com
Cc: vincent.guittot@linaro.org
Cc: bitbucket@online.de
Cc: benh@kernel.crashing.org
Cc: anton@samba.org
Cc: Morten.Rasmussen@arm.com
Cc: pjt@google.com
Cc: peterz@infradead.org
Cc: mikey@neuling.org
Link: http://lkml.kernel.org/r/20131030031252.23426.4417.stgit@preeti.in.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Preeti U Murthy 2013-10-30 08:42:52 +05:30 committed by Ingo Molnar
parent 2042abe797
commit 37dc6b50ce
3 changed files with 29 additions and 19 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

6
kernel/sched/core.c
View file

@ -4883,6 +4883,8 @@ DEFINE_PER_CPU(struct sched_domain *, sd_llc);
DEFINE_PER_CPU(int, sd_llc_size);
DEFINE_PER_CPU(int, sd_llc_id);
DEFINE_PER_CPU(struct sched_domain *, sd_numa);
DEFINE_PER_CPU(struct sched_domain *, sd_busy);
DEFINE_PER_CPU(struct sched_domain *, sd_asym);
static void update_top_cache_domain(int cpu)
{
@ -4894,6 +4896,7 @@ static void update_top_cache_domain(int cpu)
if (sd) {
id = cpumask_first(sched_domain_span(sd));
size = cpumask_weight(sched_domain_span(sd));
rcu_assign_pointer(per_cpu(sd_busy, cpu), sd->parent);
}
rcu_assign_pointer(per_cpu(sd_llc, cpu), sd);
@ -4902,6 +4905,9 @@ static void update_top_cache_domain(int cpu)
sd = lowest_flag_domain(cpu, SD_NUMA);
rcu_assign_pointer(per_cpu(sd_numa, cpu), sd);
sd = highest_flag_domain(cpu, SD_ASYM_PACKING);
rcu_assign_pointer(per_cpu(sd_asym, cpu), sd);
}
/*

40
kernel/sched/fair.c
View file

@ -6534,16 +6534,16 @@ static inline void nohz_balance_exit_idle(int cpu)
static inline void set_cpu_sd_state_busy(void)
{
struct sched_domain *sd;
int cpu = smp_processor_id();
rcu_read_lock();
sd = rcu_dereference_check_sched_domain(this_rq()->sd);
sd = rcu_dereference(per_cpu(sd_busy, cpu));
if (!sd || !sd->nohz_idle)
goto unlock;
sd->nohz_idle = 0;
for (; sd; sd = sd->parent)
atomic_inc(&sd->groups->sgp->nr_busy_cpus);
atomic_inc(&sd->groups->sgp->nr_busy_cpus);
unlock:
rcu_read_unlock();
}
@ -6551,16 +6551,16 @@ static inline void set_cpu_sd_state_busy(void)
void set_cpu_sd_state_idle(void)
{
struct sched_domain *sd;
int cpu = smp_processor_id();
rcu_read_lock();
sd = rcu_dereference_check_sched_domain(this_rq()->sd);
sd = rcu_dereference(per_cpu(sd_busy, cpu));
if (!sd || sd->nohz_idle)
goto unlock;
sd->nohz_idle = 1;
for (; sd; sd = sd->parent)
atomic_dec(&sd->groups->sgp->nr_busy_cpus);
atomic_dec(&sd->groups->sgp->nr_busy_cpus);
unlock:
rcu_read_unlock();
}
@ -6767,6 +6767,8 @@ static inline int nohz_kick_needed(struct rq *rq, int cpu)
{
unsigned long now = jiffies;
struct sched_domain *sd;
struct sched_group_power *sgp;
int nr_busy;
if (unlikely(idle_cpu(cpu)))
return 0;
@ -6792,22 +6794,22 @@ static inline int nohz_kick_needed(struct rq *rq, int cpu)
goto need_kick;
rcu_read_lock();
for_each_domain(cpu, sd) {
struct sched_group *sg = sd->groups;
struct sched_group_power *sgp = sg->sgp;
int nr_busy = atomic_read(&sgp->nr_busy_cpus);
sd = rcu_dereference(per_cpu(sd_busy, cpu));
if (sd->flags & SD_SHARE_PKG_RESOURCES && nr_busy > 1)
if (sd) {
sgp = sd->groups->sgp;
nr_busy = atomic_read(&sgp->nr_busy_cpus);
if (nr_busy > 1)
goto need_kick_unlock;
if (sd->flags & SD_ASYM_PACKING
&& (cpumask_first_and(nohz.idle_cpus_mask,
sched_domain_span(sd)) < cpu))
goto need_kick_unlock;
if (!(sd->flags & (SD_SHARE_PKG_RESOURCES | SD_ASYM_PACKING)))
break;
}
sd = rcu_dereference(per_cpu(sd_asym, cpu));
if (sd && (cpumask_first_and(nohz.idle_cpus_mask,
sched_domain_span(sd)) < cpu))
goto need_kick_unlock;
rcu_read_unlock();
return 0;

2
kernel/sched/sched.h
View file

@ -623,6 +623,8 @@ DECLARE_PER_CPU(struct sched_domain *, sd_llc);
DECLARE_PER_CPU(int, sd_llc_size);
DECLARE_PER_CPU(int, sd_llc_id);
DECLARE_PER_CPU(struct sched_domain *, sd_numa);
DECLARE_PER_CPU(struct sched_domain *, sd_busy);
DECLARE_PER_CPU(struct sched_domain *, sd_asym);
struct sched_group_power {
atomic_t ref;