Re: [PATCH tip/core/rcu 05/86] rcu: move TREE_RCU from softirq to kthread

[Yong Zhang]

On Sun, May 1, 2011 at 9:20 PM, Paul E. McKenney
<paulmck@xxxxxxxxxxxxxxxxxx> wrote:
> From: Paul E. McKenney <paul.mckenney@xxxxxxxxxx>
>
> If RCU priority boosting is to be meaningful, callback invocation must
> be boosted in addition to preempted RCU readers. ÂOtherwise, in presence
> of CPU real-time threads, the grace period ends, but the callbacks don't
> get invoked. ÂIf the callbacks don't get invoked, the associated memory
> doesn't get freed, so the system is still subject to OOM.
>
> But it is not reasonable to priority-boost RCU_SOFTIRQ, so this commit
> moves the callback invocations to a kthread, which can be boosted easily.
>
> Also add comments and properly synchronized all accesses to
> rcu_cpu_kthread_task, as suggested by Lai Jiangshan.
>
> Signed-off-by: Paul E. McKenney <paul.mckenney@xxxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> ---
[snip]
> + * Drop to non-real-time priority and yield, but only after posting a
> + * timer that will cause us to regain our real-time priority if we
> + * remain preempted. ÂEither way, we restore our real-time priority
> + * before returning.
> + */
> +static void rcu_yield(int cpu)
> +{
> + Â Â Â struct rcu_data *rdp = per_cpu_ptr(rcu_sched_state.rda, cpu);
> + Â Â Â struct sched_param sp;
> + Â Â Â struct timer_list yield_timer;
> +
> + Â Â Â setup_timer(&yield_timer, rcu_cpu_kthread_timer, (unsigned long)rdp);

setup_timer_on_stack() should be used here :)

Thanks,
Yong


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