On Tue, 2015-04-07 at 16:28 -0700, Jason Low wrote:
> Okay, so perhaps we can also try continuing nohz load balancing if we
> find that there are overloaded CPUs in the system.
Something like the following.
---
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fdae26e..d636bf7 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7620,6 +7620,16 @@ out:
}
#ifdef CONFIG_NO_HZ_COMMON
+static inline bool nohz_kick_needed(struct rq *rq);
+
+static inline void pass_nohz_balance(struct rq *this_rq, int this_cpu)
+{
+ clear_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu));
+ nohz.next_balance = jiffies;
+ if (nohz_kick_needed(this_rq))
+ nohz_balancer_kick();
+}
+
/*
* In CONFIG_NO_HZ_COMMON case, the idle balance kickee will do the
* rebalancing for all the cpus for whom scheduler ticks are stopped.
@@ -7631,8 +7641,10 @@ static void nohz_idle_balance(struct rq *this_rq, enum
cpu_idle_type idle)
int balance_cpu;
if (idle != CPU_IDLE ||
- !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu)))
- goto end;
+ !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu))) {
+ pass_nohz_balance(this_rq, this_cpu);
+ return;
+ }
for_each_cpu(balance_cpu, nohz.idle_cpus_mask) {
if (balance_cpu == this_cpu || !idle_cpu(balance_cpu))
@@ -7643,8 +7655,10 @@ static void nohz_idle_balance(struct rq *this_rq, enum
cpu_idle_type idle)
* work being done for other cpus. Next load
* balancing owner will pick it up.
*/
- if (need_resched())
- break;
+ if (need_resched()) {
+ pass_nohz_balance(this_rq, this_cpu);
+ return;
+ }
rq = cpu_rq(balance_cpu);
@@ -7664,7 +7678,6 @@ static void nohz_idle_balance(struct rq *this_rq, enum
cpu_idle_type idle)
this_rq->next_balance = rq->next_balance;
}
nohz.next_balance = this_rq->next_balance;
-end:
clear_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu));
}
@@ -7687,7 +7700,7 @@ static inline bool nohz_kick_needed(struct rq *rq)
int nr_busy, cpu = rq->cpu;
bool kick = false;
- if (unlikely(rq->idle_balance))
+ if (unlikely(idle_cpu(cpu)))
return false;
/*
@@ -7707,7 +7720,7 @@ static inline bool nohz_kick_needed(struct rq *rq)
if (time_before(now, nohz.next_balance))
return false;
- if (rq->nr_running >= 2)
+ if (rq->nr_running >= 2 || rq->rd->overload)
return true;
rcu_read_lock();
@@ -7757,16 +7770,14 @@ static void run_rebalance_domains(struct softirq_action
*h)
enum cpu_idle_type idle = this_rq->idle_balance ?
CPU_IDLE : CPU_NOT_IDLE;
+ rebalance_domains(this_rq, idle);
+
/*
* If this cpu has a pending nohz_balance_kick, then do the
* balancing on behalf of the other idle cpus whose ticks are
- * stopped. Do nohz_idle_balance *before* rebalance_domains to
- * give the idle cpus a chance to load balance. Else we may
- * load balance only within the local sched_domain hierarchy
- * and abort nohz_idle_balance altogether if we pull some load.
+ * stopped.
*/
nohz_idle_balance(this_rq, idle);
- rebalance_domains(this_rq, idle);
}
/*
--
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