On Wed, 2015-04-01 at 18:04 +0100, Morten Rasmussen wrote:
> On Wed, Apr 01, 2015 at 07:49:56AM +0100, Preeti U Murthy wrote:
> > I am sorry I don't quite get this. Can you please elaborate?
>
> I think the scenario is that we are in nohz_idle_balance() and decide to
> bail out because we have pulled some tasks, but before leaving
> nohz_idle_balance() we want to check if more balancing is necessary
> using nohz_kick_needed() and potentially kick somebody to continue.
Also, below is an example patch.
(Without the conversion to idle_cpu(), the check for rq->idle_balance
would not be accurate anymore)
---
kernel/sched/fair.c | 17 ++++++++++-------
1 files changed, 10 insertions(+), 7 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fdae26e..7749a14 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7620,6 +7620,8 @@ out:
}
#ifdef CONFIG_NO_HZ_COMMON
+static inline bool nohz_kick_needed(struct rq *rq);
+
/*
* In CONFIG_NO_HZ_COMMON case, the idle balance kickee will do the
* rebalancing for all the cpus for whom scheduler ticks are stopped.
@@ -7629,6 +7631,7 @@ static void nohz_idle_balance(struct rq *this_rq, enum
cpu_idle_type idle)
int this_cpu = this_rq->cpu;
struct rq *rq;
int balance_cpu;
+ bool done_balancing = false;
if (idle != CPU_IDLE ||
!test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu)))
@@ -7644,7 +7647,7 @@ static void nohz_idle_balance(struct rq *this_rq, enum
cpu_idle_type idle)
* balancing owner will pick it up.
*/
if (need_resched())
- break;
+ goto end;
rq = cpu_rq(balance_cpu);
@@ -7663,9 +7666,12 @@ static void nohz_idle_balance(struct rq *this_rq, enum
cpu_idle_type idle)
if (time_after(this_rq->next_balance, rq->next_balance))
this_rq->next_balance = rq->next_balance;
}
+ done_balancing = true;
nohz.next_balance = this_rq->next_balance;
end:
clear_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu));
+ if (!done_balancing && nohz_kick_needed(this_rq))
+ nohz_balancer_kick();
}
/*
@@ -7687,7 +7693,7 @@ 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;
/*
@@ -7757,16 +7763,13 @@ 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);
}
/*
--
1.7.2.5
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