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

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Message-ID: <1322062966.17693.44.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC>
Date:	Wed, 23 Nov 2011 16:42:46 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jun Zhao <mypopydev@...il.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH] ipv4 : igmp : optimize timer modify logic in
 igmp_mod_timer()

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 ?

>  			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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