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rcu: put per-CPU kthread at non-RT priority during CPU hotplug operations 

If you are doing CPU hotplug operations, it is best not to have
CPU-bound realtime tasks running CPU-bound on the outgoing CPU.
So this commit makes per-CPU kthreads run at non-realtime priority
during that time.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
This commit is contained in:
Paul E. McKenney 2011-04-18 15:31:26 -07:00 committed by Paul E. McKenney
parent 0f962a5e72
commit e3995a25fa
1 changed files with 26 additions and 0 deletions
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26
kernel/rcutree.c
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@ -1463,6 +1463,30 @@ static void invoke_rcu_node_kthread(struct rcu_node *rnp)
wake_up_process(t);
}
/*
* Set the specified CPU's kthread to run RT or not, as specified by
* the to_rt argument. The CPU-hotplug locks are held, so the task
* is not going away.
*/
static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
{
int policy;
struct sched_param sp;
struct task_struct *t;
t = per_cpu(rcu_cpu_kthread_task, cpu);
if (t == NULL)
return;
if (to_rt) {
policy = SCHED_FIFO;
sp.sched_priority = RCU_KTHREAD_PRIO;
} else {
policy = SCHED_NORMAL;
sp.sched_priority = 0;
}
sched_setscheduler_nocheck(t, policy, &sp);
}
/*
* Timer handler to initiate the waking up of per-CPU kthreads that
* have yielded the CPU due to excess numbers of RCU callbacks.
@ -2166,9 +2190,11 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
case CPU_ONLINE:
case CPU_DOWN_FAILED:
rcu_node_kthread_setaffinity(rnp, -1);
rcu_cpu_kthread_setrt(cpu, 1);
break;
case CPU_DOWN_PREPARE:
rcu_node_kthread_setaffinity(rnp, cpu);
rcu_cpu_kthread_setrt(cpu, 0);
break;
case CPU_DYING:
case CPU_DYING_FROZEN: