Re: [PATCH tip/core/rcu 3/7] rcu: Kick adaptive-ticks CPUs that are holding up RCU grace periods

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Sat, Apr 13, 2013 at 04:06:58PM +0200, Frederic Weisbecker wrote:
> 2013/4/13 Paul E. McKenney <paulmck@linux.vnet.ibm.com>:
> > From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> >
> > Adaptive-ticks CPUs inform RCU when they enter kernel mode, but they do
> > not necessarily turn the scheduler-clock tick back on.  This state of
> > affairs could result in RCU waiting on an adaptive-ticks CPU running
> > for an extended period in kernel mode.  Such a CPU will never run the
> > RCU state machine, and could therefore indefinitely extend the RCU state
> > machine, sooner or later resulting in an OOM condition.
> >
> > This patch, inspired by an earlier patch by Frederic Weisbecker, therefore
> > causes RCU's force-quiescent-state processing to check for this condition
> > and to send an IPI to CPUs that remain in that state for too long.
> > "Too long" currently means about three jiffies by default, which is
> > quite some time for a CPU to remain in the kernel without blocking.
> > The rcu_tree.jiffies_till_first_fqs and rcutree.jiffies_till_next_fqs
> > sysfs variables may be used to tune "too long" if needed.
> >
> > Reported-by: Frederic Weisbecker <fweisbec@gmail.com>
> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> 
> It might be better if I take this patch to get it through
> tip:timers/nohz so that I can keep it in sync with the rest. What do
> you think?

Works for me!  Let me know when you have picked it up and I will drop
it from my tree.

							Thanx, Paul