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sched: Ensure cpu_power periodic update

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With a lot of small tasks, the softirq sched is nearly never called
when no_hz is enabled. In this case load_balance() is mainly called
with the newly_idle mode which doesn't update the cpu_power.

Add a next_update field which ensure a maximum update period when
there is short activity.

Having stale cpu_power information can skew the load-balancing
decisions, this is cured by the guaranteed update.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1323717668-2143-1-git-send-email-vincent.guittot@linaro.org
This commit is contained in:
Vincent Guittot 2011-12-12 20:21:08 +01:00 committed by Ingo Molnar
parent 39be350127
commit 4ec4412e1e
2 changed files with 17 additions and 8 deletions
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1
include/linux/sched.h
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@ -905,6 +905,7 @@ struct sched_group_power {
* single CPU. * single CPU.
*/ */
unsigned int power, power_orig; unsigned int power, power_orig;
unsigned long next_update;
/* /*
* Number of busy cpus in this group. * Number of busy cpus in this group.
*/ */

24
kernel/sched/fair.c
View file

@ -215,6 +215,8 @@ calc_delta_mine(unsigned long delta_exec, unsigned long weight,
const struct sched_class fair_sched_class; const struct sched_class fair_sched_class;
static unsigned long __read_mostly max_load_balance_interval = HZ/10;
/************************************************************** /**************************************************************
* CFS operations on generic schedulable entities: * CFS operations on generic schedulable entities:
*/ */
@ -3776,6 +3778,11 @@ void update_group_power(struct sched_domain *sd, int cpu)
struct sched_domain *child = sd->child; struct sched_domain *child = sd->child;
struct sched_group *group, *sdg = sd->groups; struct sched_group *group, *sdg = sd->groups;
unsigned long power; unsigned long power;
unsigned long interval;
interval = msecs_to_jiffies(sd->balance_interval);
interval = clamp(interval, 1UL, max_load_balance_interval);
sdg->sgp->next_update = jiffies + interval;
if (!child) { if (!child) {
update_cpu_power(sd, cpu); update_cpu_power(sd, cpu);
@ -3883,12 +3890,15 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
* domains. In the newly idle case, we will allow all the cpu's * domains. In the newly idle case, we will allow all the cpu's
* to do the newly idle load balance. * to do the newly idle load balance.
*/ */
if (idle != CPU_NEWLY_IDLE && local_group) { if (local_group) {
if (balance_cpu != this_cpu) { if (idle != CPU_NEWLY_IDLE) {
*balance = 0; if (balance_cpu != this_cpu) {
return; *balance = 0;
} return;
update_group_power(sd, this_cpu); }
update_group_power(sd, this_cpu);
} else if (time_after_eq(jiffies, group->sgp->next_update))
update_group_power(sd, this_cpu);
} }
/* Adjust by relative CPU power of the group */ /* Adjust by relative CPU power of the group */
@ -4945,8 +4955,6 @@ static int __cpuinit sched_ilb_notifier(struct notifier_block *nfb,
static DEFINE_SPINLOCK(balancing); static DEFINE_SPINLOCK(balancing);
static unsigned long __read_mostly max_load_balance_interval = HZ/10;
/* /*
* Scale the max load_balance interval with the number of CPUs in the system. * Scale the max load_balance interval with the number of CPUs in the system.
* This trades load-balance latency on larger machines for less cross talk. * This trades load-balance latency on larger machines for less cross talk.