netdev - Re: [PATCH 2/2] net: neighbor timer power saving

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Date:	Wed, 19 Dec 2007 08:23:43 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Stephen Hemminger <shemminger@...ux-foundation.org>
CC:	parag.warudkar@...il.com, David Miller <davem@...emloft.net>,
	netdev@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH 2/2] net: neighbor timer power saving

Stephen Hemminger a écrit :
> The neighbor GC timer runs once a second, but it doesn't need to wake
> up the machine.
> 
> Signed-off-by: Stephen Hemminger <shemminger@...tta.com>
> 
> --- a/net/core/neighbour.c	2007-12-18 07:46:07.000000000 -0800
> +++ b/net/core/neighbour.c	2007-12-18 07:47:36.000000000 -0800
> @@ -270,7 +270,7 @@ static struct neighbour *neigh_alloc(str
>  	n->nud_state	  = NUD_NONE;
>  	n->output	  = neigh_blackhole;
>  	n->parms	  = neigh_parms_clone(&tbl->parms);
> -	init_timer(&n->timer);
> +	init_timer_deferrable(&n->timer);
>  	n->timer.function = neigh_timer_handler;
>  	n->timer.data	  = (unsigned long)n;
>  
> @@ -740,7 +740,7 @@ static void neigh_timer_handler(unsigned
>  
>  	state = neigh->nud_state;
>  	now = jiffies;
> -	next = now + HZ;
> +	next = round_jiffies(now + HZ);
>  
>  	if (!(state & NUD_IN_TIMER)) {
>  #ifndef CONFIG_SMP
> @@ -1372,7 +1372,7 @@ void neigh_table_init_no_netlink(struct 
>  	get_random_bytes(&tbl->hash_rnd, sizeof(tbl->hash_rnd));
>  
>  	rwlock_init(&tbl->lock);
> -	init_timer(&tbl->gc_timer);
> +	init_timer_deferrable(&tbl->gc_timer);
>  	tbl->gc_timer.data     = (unsigned long)tbl;
>  	tbl->gc_timer.function = neigh_periodic_timer;
>  	tbl->gc_timer.expires  = now + 1;

I wonder if this deferrable timer thing is the right way to go.

(like read_mostly thing if you want :) )

We are going to convert 99% timers to deferrable.

Maybe the right move should be to have the reverse attribute, to mark a timer 
as non deferrable...

Also, why use round_jiffies() on a deferrable timer ? That sounds unecessary ?

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