Re: [PATCH net-next] igmp: hash a hash table to speedup ip_check_mc_rcu()

[Cong Wang <xiyou.wangcong@gmail.com>]

On Fri, 07 Jun 2013 at 15:48 GMT, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> diff --git a/include/linux/igmp.h b/include/linux/igmp.h
> index 7f2bf15..e3362b5 100644
> --- a/include/linux/igmp.h
> +++ b/include/linux/igmp.h
> @@ -84,6 +84,7 @@ struct ip_mc_list {
>  		struct ip_mc_list *next;
>  		struct ip_mc_list __rcu *next_rcu;
>  	};
> +	struct ip_mc_list __rcu *next_hash;


Why not put this into the above union?


> +static void ip_mc_hash_add(struct in_device *in_dev,
> +			   struct ip_mc_list *im)
> +{
> +	struct ip_mc_list __rcu **mc_hash;
> +	u32 hash;
> +
> +	mc_hash = rtnl_dereference(in_dev->mc_hash);
> +	if (mc_hash) {
> +		hash = ip_mc_hash(im);
> +		im->next_hash = rtnl_dereference(mc_hash[hash]);
> +		rcu_assign_pointer(mc_hash[hash], im);
> +		return;
> +	}
> +
> +	/* do not use a hash table for small number of items */
> +	if (in_dev->mc_count < 4)
> +		return;


Can this check be moved to the beginning of this function?


> +
> +	mc_hash = kzalloc(sizeof(struct ip_mc_list *) << MC_HASH_SZ_LOG,
> +			  GFP_KERNEL);
> +	if (!mc_hash)
> +		return;
> +
> +	for_each_pmc_rtnl(in_dev, im) {
> +		hash = ip_mc_hash(im);
> +		im->next_hash = rtnl_dereference(mc_hash[hash]);
> +		RCU_INIT_POINTER(mc_hash[hash], im);
> +	}
> +
> +	rcu_assign_pointer(in_dev->mc_hash, mc_hash);
> +}
> +

Thanks!