On Fri, 2012-09-07 at 09:20 +0800, Fengguang Wu wrote:
> FYI, the bisect result is
>
> commit 554cecaf733623b327eef9652b65965eb1081b81
> Author: Diwakar Tundlam <dtund...@nvidia.com>
> Date: Wed Mar 7 14:44:26 2012 -0800
>
> sched/nohz: Correctly initialize 'next_balance' in 'nohz' idle balancer
>
> The 'next_balance' field of 'nohz' idle balancer must be initialized
> to jiffies. Since jiffies is initialized to negative 300 seconds the
> 'nohz' idle balancer does not run for the first 300s (5mins) after
> bootup. If no new processes are spawed or no idle cycles happen, the
> load on the cpus will remain unbalanced for that duration.
>
> Signed-off-by: Diwakar Tundlam <dtund...@nvidia.com>
> Signed-off-by: Peter Zijlstra <a.p.zijls...@chello.nl>
> Link:
> http://lkml.kernel.org/r/1dd7bfedd3147247b1355befefe4665237994f3...@hqmail04.nvidia.com
> Signed-off-by: Ingo Molnar <mi...@elte.hu>
Oh fun.. does the below 'fix' it?
The thing I'm thinking of a tick happening right after we set jiffies
but before the zalloc (specifically the memset(0)) is complete. Since
we've already registered the softirq we can end up in the load-balancer
and see a completely weird idle mask.
Hmm?
---
kernel/sched/fair.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1ca4fe4..ac57bb6 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5346,13 +5346,12 @@ void print_cfs_stats(struct seq_file *m, int
cpu)
__init void init_sched_fair_class(void)
{
#ifdef CONFIG_SMP
- open_softirq(SCHED_SOFTIRQ, run_rebalance_domains);
-
#ifdef CONFIG_NO_HZ
nohz.next_balance = jiffies;
zalloc_cpumask_var(&nohz.idle_cpus_mask, GFP_NOWAIT);
cpu_notifier(sched_ilb_notifier, 0);
#endif
-#endif /* SMP */
+ open_softirq(SCHED_SOFTIRQ, run_rebalance_domains);
+#endif /* SMP */
}
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