linux-kernel - Re: [PATCH v2 1/2] sched: Add cond_resched_rcu

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Date:	Tue, 30 Apr 2013 16:29:44 +0900
From:	Simon Horman <horms@...ge.net.au>
To:	Julian Anastasov <ja@....bg>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.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>
Subject: Re: [PATCH v2 1/2] sched: Add cond_resched_rcu_lock() helper

On Tue, Apr 30, 2013 at 10:12:38AM +0300, Julian Anastasov wrote:
> 
> 	Hello,
> 
> On Tue, 30 Apr 2013, Simon Horman wrote:
> 
> > This is intended for use in loops which read data protected by RCU and may
> > have a large number of iterations.  Such an example is dumping the list of
> > connections known to IPVS: ip_vs_conn_array() and ip_vs_conn_seq_next().
> > 
> > The call to cond_resched() is guarded by #ifndef CONFIG_PREEMPT_RCU as in
> > the case of CONFIG_PREEMPT_RCU _rcu_read_unlock() will check to see if the
> > RCU core needs to be informed, so there is no need to invoke cond_resched()
> > in that case. Thanks to Paul E. McKenney for explaining this.
> > 
> > cond_resched_rcu_lock() suggested by Eric Dumazet.
> > ifndef guard suggested by Paul E. McKenney and Julian Anastasov.
> > 
> > Cc: Eric Dumazet <eric.dumazet@...il.com>
> > Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > Cc: Julian Anastasov <ja@....bg>
> > Acked-by: Ingo Molnar <mingo@...nel.org>
> > Signed-off-by: Simon Horman <horms@...ge.net.au>
> > 
> > ---
> > 
> > v2
> > * Add guard the call to cond_resched()
> > ---
> >  include/linux/sched.h | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> > 
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index e692a02..66da71c 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -2787,3 +2787,14 @@ static inline unsigned long rlimit_max(unsigned int limit)
> >  }
> >  
> >  #endif
> > +
> > +static void inline cond_resched_rcu_lock(void)
> > +{
> > +	if (need_resched()) {
> 
> 	Ops, it should be without above need_resched.

Thanks, to clarify, just this:

static void inline cond_resched_rcu_lock(void)
{
	rcu_read_unlock();
#ifndef CONFIG_PREEMPT_RCU
	cond_resched();
#endif
	rcu_read_lock();
}
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