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

To: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Subject: Re: [PATCH 2/2] ipvs: Use cond_resched_rcu_lock() helper when dumping connections
Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Simon Horman <horms@xxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, lvs-devel@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxxxxxx, netfilter-devel@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>, Dipankar Sarma <dipankar@xxxxxxxxxx>, dhaval.giani@xxxxxxxxx
From: Julian Anastasov <ja@xxxxxx>
Date: Tue, 30 Apr 2013 00:08:18 +0300 (EEST)

On Sat, 27 Apr 2013, Paul E. McKenney wrote:

> On Sat, Apr 27, 2013 at 02:32:48PM +0300, Julian Anastasov wrote:
> > 
> >     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?:
> > 
> >     rcu_read_unlock();
> > #if !defined(CONFIG_PREEMPT) || defined(CONFIG_PREEMPT_RCU)
> I would instead suggest something like:
> But yes, in the CONFIG_PREEMPT_RCU case, the cond_resched() is not
> needed.

        Hm, is this correct? If I follow the ifdefs
preempt_schedule is called when CONFIG_PREEMPT is
defined _and_ CONFIG_PREEMPT_RCU is not defined.
Your example for CONFIG_PREEMPT_RCU is the opposite to this?

>                                                       Thanx, Paul
> >     cond_resched();
> > #endif
> >     rcu_read_lock();


Julian Anastasov <ja@xxxxxx>
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