netdev - Re: [PATCHv2 net-next] neigh: support smaller retrans

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Message-ID: <82a99a95-9a8c-48e8-133a-f249b5a25f3b@gmail.com>
Date:   Tue, 31 Mar 2020 19:36:49 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Hangbin Liu <liuhangbin@...il.com>, netdev@...r.kernel.org
Cc:     David Miller <davem@...emloft.net>
Subject: Re: [PATCHv2 net-next] neigh: support smaller retrans_time settting



On 3/31/20 7:07 PM, Hangbin Liu wrote:
> Currently, we limited the retrans_time to be greater than HZ/2. i.e.
> setting retrans_time less than 500ms will not work. This makes the user
> unable to achieve a more accurate control for bonding arp fast failover.
> 
> Update the sanity check to HZ/100, which is 10ms, to let users have more
> ability on the retrans_time control.
> 
> v2: use HZ instead of hard code number
> 
> Signed-off-by: Hangbin Liu <liuhangbin@...il.com>
> ---
>  net/core/neighbour.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> index 5bf8d22a47ec..46a5611a9f3d 100644
> --- a/net/core/neighbour.c
> +++ b/net/core/neighbour.c
> @@ -1125,7 +1125,7 @@ int __neigh_event_send(struct neighbour *neigh, struct sk_buff *skb)
>  			neigh->nud_state     = NUD_INCOMPLETE;
>  			neigh->updated = now;
>  			next = now + max(NEIGH_VAR(neigh->parms, RETRANS_TIME),
> -					 HZ/2);
> +					 HZ/100);
>  			neigh_add_timer(neigh, next);
>  			immediate_probe = true;
>  		} else {
> 

Note that IPv6 has a different limit (HZ/10)

It would be nice to have converged values.