netdev - Re: [PATCH] ipv4 : igmp : optimize timer modify logic in igmp_mod

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Date:	Wed, 23 Nov 2011 23:44:36 +0800
From:	Jun Zhao <mypopydev@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH] ipv4 : igmp : optimize timer modify logic in
 igmp_mod_timer()

On Wed, 2011-11-23 at 16:42 +0100, Eric Dumazet wrote:
> Le mercredi 23 novembre 2011 à 23:26 +0800, Jun Zhao a écrit :
> > When timer is pending and expires less-than-or-equal-to new delay,
> > we need not used del_timer()/add_timer().
> > 
> > Signed-off-by: Jun Zhao <mypopydev@...il.com>
> > ---
> >  net/ipv4/igmp.c |   12 ++++++------
> >  1 files changed, 6 insertions(+), 6 deletions(-)
> > 
> > diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
> > index c7472ef..50d06c5 100644
> > --- a/net/ipv4/igmp.c
> > +++ b/net/ipv4/igmp.c
> > @@ -215,14 +215,14 @@ static void igmp_mod_timer(struct ip_mc_list *im, int max_delay)
> >  {
> >  	spin_lock_bh(&im->lock);
> >  	im->unsolicit_count = 0;
> > -	if (del_timer(&im->timer)) {
> > -		if ((long)(im->timer.expires-jiffies) < max_delay) {
> > -			add_timer(&im->timer);
> > -			im->tm_running = 1;
> > -			spin_unlock_bh(&im->lock);
> > +	if (timer_pending(&im->timer)) {
> > +		if (time_before_eq(im->timer.expires, (jiffies + max_delay))) {
> > +			spin_lock_bh(&im->lock);
> 
> And you actually tested this patch ?

Sorry for this mistake. :(.  spin_lock_bh -> spin_unlock_bh

> 
> >  			return;
> > +		} else {
> > +			del_timer(&im->timer);
> > +			atomic_dec(&im->refcnt);
> >  		}
> > -		atomic_dec(&im->refcnt);
> >  	}
> >  	igmp_start_timer(im, max_delay);
> >  	spin_unlock_bh(&im->lock);
> 
> 
> Not sure why you want to optimize this very rare function call, risking
> adding bugs in it.
> 
> 
> 


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