rcu: Cure load woes
Commit cc3ce5176d83 (rcu: Start RCU kthreads in TASK_INTERRUPTIBLE
state) fudges a sleeping task' state, resulting in the scheduler seeing
a TASK_UNINTERRUPTIBLE task going to sleep, but a TASK_INTERRUPTIBLE
task waking up. The result is unbalanced load calculation.
The problem that patch tried to address is that the RCU threads could
stay in UNINTERRUPTIBLE state for quite a while and triggering the hung
task detector due to on-demand wake-ups.
Cure the problem differently by always giving the tasks at least one
wake-up once the CPU is fully up and running, this will kick them out of
the initial UNINTERRUPTIBLE state and into the regular INTERRUPTIBLE
wait state.
[ The alternative would be teaching kthread_create() to start threads as
INTERRUPTIBLE but that needs a tad more thought. ]
Reported-by: Damien Wyart <damien.wyart@free.fr>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Paul E. McKenney <paul.mckenney@linaro.org>
Link: http://lkml.kernel.org/r/1306755291.1200.2872.camel@twins
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index a767b7d..c8bff30 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -1295,7 +1295,6 @@
if (IS_ERR(t))
return PTR_ERR(t);
raw_spin_lock_irqsave(&rnp->lock, flags);
- set_task_state(t, TASK_INTERRUPTIBLE);
rnp->boost_kthread_task = t;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
sp.sched_priority = RCU_KTHREAD_PRIO;
@@ -1303,6 +1302,12 @@
return 0;
}
+static void __cpuinit rcu_wake_one_boost_kthread(struct rcu_node *rnp)
+{
+ if (rnp->boost_kthread_task)
+ wake_up_process(rnp->boost_kthread_task);
+}
+
#else /* #ifdef CONFIG_RCU_BOOST */
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
@@ -1326,6 +1331,10 @@
return 0;
}
+static void __cpuinit rcu_wake_one_boost_kthread(struct rcu_node *rnp)
+{
+}
+
#endif /* #else #ifdef CONFIG_RCU_BOOST */
#ifndef CONFIG_SMP