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

To: Ingo Molnar <mingo@xxxxxxxxxx>
Subject: Re: [PATCH 2/2] ipvs: Use cond_resched_rcu_lock() helper when dumping connections
Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx>, Julian Anastasov <ja@xxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, lvs-devel@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxxxxxx, netfilter-devel@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>, Dipankar Sarma <dipankar@xxxxxxxxxx>, "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
From: Simon Horman <horms@xxxxxxxxxxxx>
Date: Tue, 30 Apr 2013 11:45:52 +0900
On Fri, Apr 26, 2013 at 08:15:34AM +0200, Ingo Molnar wrote:
> 
> * Simon Horman <horms@xxxxxxxxxxxx> wrote:
> 
> > This avoids the situation where a dump of a large number of connections
> > may prevent scheduling for a long time while also avoiding excessive
> > calls to rcu_read_unlock() and rcu_read_lock().
> > 
> > Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx>
> > Cc: Julian Anastasov <ja@xxxxxx>
> > Signed-off-by: Simon Horman <horms@xxxxxxxxxxxx>
> > ---
> >  net/netfilter/ipvs/ip_vs_conn.c | 6 ++----
> >  1 file changed, 2 insertions(+), 4 deletions(-)
> > 
> > diff --git a/net/netfilter/ipvs/ip_vs_conn.c 
> > b/net/netfilter/ipvs/ip_vs_conn.c
> > index a083bda..42a7b33 100644
> > --- a/net/netfilter/ipvs/ip_vs_conn.c
> > +++ b/net/netfilter/ipvs/ip_vs_conn.c
> > @@ -975,8 +975,7 @@ static void *ip_vs_conn_array(struct seq_file *seq, 
> > loff_t pos)
> >                             return cp;
> >                     }
> >             }
> > -           rcu_read_unlock();
> > -           rcu_read_lock();
> > +           cond_resched_rcu_lock();
> >     }
> >  
> >     return NULL;
> > @@ -1015,8 +1014,7 @@ static void *ip_vs_conn_seq_next(struct seq_file 
> > *seq, void *v, loff_t *pos)
> >                     iter->l = &ip_vs_conn_tab[idx];
> >                     return cp;
> >             }
> > -           rcu_read_unlock();
> > -           rcu_read_lock();
> > +           cond_resched_rcu_lock();
> 
> Feel free to route this via the networking tree.
> 
> Note that this change isn't a pure clean-up but has functional effects as 
> well: on !PREEMPT or PREEMPT_VOLUNTARY kernels it will add in a potential 
> cond_resched() - while previously it would only rcu unlock and relock 
> (which in itself isn't scheduling).
> 
> This should probably be pointed out in the changelog.

Thanks, I have added some text which I will include in v2.
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