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