Re: [PATCH 2/2] ipvs: Use cond_resched_rcu_lock() helper when dumpingconnections

From: Julian Anastasov
Date: Sat Apr 27 2013 - 07:40:17 EST


On Fri, 26 Apr 2013, Eric Dumazet wrote:

> On Fri, 2013-04-26 at 10:48 -0700, Paul E. McKenney wrote:
> > Don't get me wrong, I am not opposing cond_resched_rcu_lock() because it
> > will be difficult to validate. For one thing, until there are a lot of
> > them, manual inspection is quite possible. So feel free to apply my
> > Acked-by to the patch.
> One question : If some thread(s) is(are) calling rcu_barrier() and
> waiting we exit from rcu_read_lock() section, is need_resched() enough
> for allowing to break the section ?
> If not, maybe we should not test need_resched() at all.
> rcu_read_unlock();
> cond_resched();
> rcu_read_lock();

So, I assume, to help realtime kernels and rcu_barrier
it is not a good idea to guard rcu_read_unlock with checks.
I see that rcu_read_unlock will try to reschedule in the
!CONFIG_PREEMPT_RCU case (via preempt_enable), can we
use ifdefs to avoid double TIF_NEED_RESCHED check?:

#if !defined(CONFIG_PREEMPT) || defined(CONFIG_PREEMPT_RCU)


Julian Anastasov <ja@xxxxxx>
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