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Subject[tip:sched/core] sched/balancing: Periodically decay max cost of idle balance
Commit-ID:  f48627e686a69f5215cb0761e731edb3d9859dd9
Gitweb: http://git.kernel.org/tip/f48627e686a69f5215cb0761e731edb3d9859dd9
Author: Jason Low <jason.low2@hp.com>
AuthorDate: Fri, 13 Sep 2013 11:26:53 -0700
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 20 Sep 2013 12:03:46 +0200

sched/balancing: Periodically decay max cost of idle balance

This patch builds on patch 2 and periodically decays that max value to
do idle balancing per sched domain by approximately 1% per second. Also
decay the rq's max_idle_balance_cost value.

Signed-off-by: Jason Low <jason.low2@hp.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1379096813-3032-4-git-send-email-jason.low2@hp.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/metag/include/asm/topology.h | 1 +
include/linux/sched.h | 3 +++
include/linux/topology.h | 3 +++
kernel/sched/fair.c | 38 +++++++++++++++++++++++++++++++-------
4 files changed, 38 insertions(+), 7 deletions(-)

diff --git a/arch/metag/include/asm/topology.h b/arch/metag/include/asm/topology.h
index db19292..8e9c0b3 100644
--- a/arch/metag/include/asm/topology.h
+++ b/arch/metag/include/asm/topology.h
@@ -27,6 +27,7 @@
.balance_interval = 1, \
.nr_balance_failed = 0, \
.max_newidle_lb_cost = 0, \
+ .next_decay_max_lb_cost = jiffies, \
}

#define cpu_to_node(cpu) ((void)(cpu), 0)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index be078ff..b5344de 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -810,7 +810,10 @@ struct sched_domain {
unsigned int nr_balance_failed; /* initialise to 0 */

u64 last_update;
+
+ /* idle_balance() stats */
u64 max_newidle_lb_cost;
+ unsigned long next_decay_max_lb_cost;

#ifdef CONFIG_SCHEDSTATS
/* load_balance() stats */
diff --git a/include/linux/topology.h b/include/linux/topology.h
index e2a2c3d..12ae6ce 100644
--- a/include/linux/topology.h
+++ b/include/linux/topology.h
@@ -107,6 +107,7 @@ int arch_update_cpu_topology(void);
.balance_interval = 1, \
.smt_gain = 1178, /* 15% */ \
.max_newidle_lb_cost = 0, \
+ .next_decay_max_lb_cost = jiffies, \
}
#endif
#endif /* CONFIG_SCHED_SMT */
@@ -137,6 +138,7 @@ int arch_update_cpu_topology(void);
.last_balance = jiffies, \
.balance_interval = 1, \
.max_newidle_lb_cost = 0, \
+ .next_decay_max_lb_cost = jiffies, \
}
#endif
#endif /* CONFIG_SCHED_MC */
@@ -169,6 +171,7 @@ int arch_update_cpu_topology(void);
.last_balance = jiffies, \
.balance_interval = 1, \
.max_newidle_lb_cost = 0, \
+ .next_decay_max_lb_cost = jiffies, \
}
#endif

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index ffc99d8..2b89cd2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5681,15 +5681,39 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle)
/* Earliest time when we have to do rebalance again */
unsigned long next_balance = jiffies + 60*HZ;
int update_next_balance = 0;
- int need_serialize;
+ int need_serialize, need_decay = 0;
+ u64 max_cost = 0;

update_blocked_averages(cpu);

rcu_read_lock();
for_each_domain(cpu, sd) {
+ /*
+ * Decay the newidle max times here because this is a regular
+ * visit to all the domains. Decay ~1% per second.
+ */
+ if (time_after(jiffies, sd->next_decay_max_lb_cost)) {
+ sd->max_newidle_lb_cost =
+ (sd->max_newidle_lb_cost * 253) / 256;
+ sd->next_decay_max_lb_cost = jiffies + HZ;
+ need_decay = 1;
+ }
+ max_cost += sd->max_newidle_lb_cost;
+
if (!(sd->flags & SD_LOAD_BALANCE))
continue;

+ /*
+ * Stop the load balance at this level. There is another
+ * CPU in our sched group which is doing load balancing more
+ * actively.
+ */
+ if (!continue_balancing) {
+ if (need_decay)
+ continue;
+ break;
+ }
+
interval = sd->balance_interval;
if (idle != CPU_IDLE)
interval *= sd->busy_factor;
@@ -5723,14 +5747,14 @@ out:
next_balance = sd->last_balance + interval;
update_next_balance = 1;
}
-
+ }
+ if (need_decay) {
/*
- * Stop the load balance at this level. There is another
- * CPU in our sched group which is doing load balancing more
- * actively.
+ * Ensure the rq-wide value also decays but keep it at a
+ * reasonable floor to avoid funnies with rq->avg_idle.
*/
- if (!continue_balancing)
- break;
+ rq->max_idle_balance_cost =
+ max((u64)sysctl_sched_migration_cost, max_cost);
}
rcu_read_unlock();


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