With a lot of small task, the softirq sched is nearly never called
when no_hz is enable. Te 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
Signed-off-by: Vincent Guittot <vincent.guit...@linaro.org>
---
include/linux/sched.h | 1 +
kernel/sched_fair.c | 24 ++++++++++++++++--------
2 files changed, 17 insertions(+), 8 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 41d0237..8610921 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -901,6 +901,7 @@ struct sched_group_power {
* single CPU.
*/
unsigned int power, power_orig;
+ unsigned long next_update;
};
struct sched_group {
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index bc8ee99..320b7a0 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -91,6 +91,8 @@ unsigned int __read_mostly sysctl_sched_shares_window =
10000000UL;
static const struct sched_class fair_sched_class;
+static unsigned long __read_mostly max_load_balance_interval = HZ/10;
+
/**************************************************************
* CFS operations on generic schedulable entities:
*/
@@ -2667,6 +2669,11 @@ static void update_group_power(struct sched_domain *sd,
int cpu)
struct sched_domain *child = sd->child;
struct sched_group *group, *sdg = sd->groups;
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) {
update_cpu_power(sd, cpu);
@@ -2774,12 +2781,15 @@ static inline void update_sg_lb_stats(struct
sched_domain *sd,
* domains. In the newly idle case, we will allow all the cpu's
* to do the newly idle load balance.
*/
- if (idle != CPU_NEWLY_IDLE && local_group) {
- if (balance_cpu != this_cpu) {
- *balance = 0;
- return;
- }
- update_group_power(sd, this_cpu);
+ if (local_group) {
+ if (idle != CPU_NEWLY_IDLE) {
+ if (balance_cpu != this_cpu) {
+ *balance = 0;
+ return;
+ }
+ 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 */
@@ -3879,8 +3889,6 @@ void select_nohz_load_balancer(int stop_tick)
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.
* This trades load-balance latency on larger machines for less cross talk.
--
1.7.4.1
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