linux-kernel - Re: [PATCH 2/2] ipvs: Use cond_resched_rcu_lock() helper when dumping connections

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Message-ID: <alpine.LFD.2.00.1304292356220.1822@ja.ssi.bg>
Date:	Tue, 30 Apr 2013 00:08:18 +0300 (EEST)
From:	Julian Anastasov <ja@....bg>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Simon Horman <horms@...ge.net.au>,
	Ingo Molnar <mingo@...hat.com>, lvs-devel@...r.kernel.org,
	netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Pablo Neira Ayuso <pablo@...filter.org>,
	Dipankar Sarma <dipankar@...ibm.com>, dhaval.giani@...il.com
Subject: Re: [PATCH 2/2] ipvs: Use cond_resched_rcu_lock() helper when dumping
 connections


	Hello,

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:
> 
> #ifndef CONFIG_PREEMPT_RCU
> 
> 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();

Regards

--
Julian Anastasov <ja@....bg>
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