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

Paul E. McKenney
2011-05-06T05:47:06Z

On Thu, May 05, 2011 at 05:31:35PM +0800, Yong Zhang wrote:
> On Sun, May 1, 2011 at 9:20 PM, Paul E. McKenney
> <paulmck@linux.vnet.ibm.com> wrote:
> > From: Paul E. McKenney <paul.mckenney@linaro.org>
> >
> > If RCU priority boosting is to be meaningful, callback invocation must
> > be boosted in addition to preempted RCU readers.  Otherwise, in presence
> > of CPU real-time threads, the grace period ends, but the callbacks don't
> > get invoked.  If 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@linaro.org>
> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > ---
> [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.  Either way, we restore our real-time priority
> > + * before returning.
> > + */
> > +static void rcu_yield(int cpu)
> > +{
> > +       struct rcu_data *rdp = per_cpu_ptr(rcu_sched_state.rda, cpu);
> > +       struct sched_param sp;
> > +       struct timer_list yield_timer;
> > +
> > +       setup_timer(&yield_timer, rcu_cpu_kthread_timer, (unsigned long)rdp);
>
> setup_timer_on_stack() should be used here :)

Good eyes!!! Fixed, will update the -rcu git tree.

Thanx, Paul