netdev - Re: [rfc] IPVS: convert scheduler management to RCU

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Date:	Fri, 20 Aug 2010 21:44:08 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Simon Horman <horms@...ge.net.au>
Cc:	lvs-devel@...r.kernel.org, netdev@...r.kernel.org,
	netfilter-devel@...r.kernel.org,
	Stephen Hemminger <shemminger@...tta.com>,
	Wensong Zhang <wensong@...ux-vs.org>,
	Julian Anastasov <ja@....bg>,
	Paul E McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: [rfc] IPVS: convert scheduler management to RCU

On Fri, Aug 20, 2010 at 9:33 PM, Simon Horman <horms@...ge.net.au> wrote:
> Signed-off-by: Simon Horman <horms@...ge.net.au>
>
> ---
>
> I'm still getting my head around RCU, so review would be greatly appreciated.
>
> It occurs to me that this code is not performance critical, so
> perhaps simply replacing the rwlock with a spinlock would be better?
>
> Index: nf-next-2.6/net/netfilter/ipvs/ip_vs_sched.c
> ===================================================================
> --- nf-next-2.6.orig/net/netfilter/ipvs/ip_vs_sched.c   2010-08-20 22:21:01.000000000 +0900
> +++ nf-next-2.6/net/netfilter/ipvs/ip_vs_sched.c        2010-08-20 22:21:51.000000000 +0900
> @@ -35,7 +35,7 @@
>  static LIST_HEAD(ip_vs_schedulers);
>
>  /* lock for service table */
> -static DEFINE_RWLOCK(__ip_vs_sched_lock);
> +static DEFINE_SPINLOCK(ip_vs_sched_mutex);
>
>
>  /*
> @@ -91,9 +91,9 @@ static struct ip_vs_scheduler *ip_vs_sch
>
>        IP_VS_DBG(2, "%s(): sched_name \"%s\"\n", __func__, sched_name);
>
> -       read_lock_bh(&__ip_vs_sched_lock);
> +       rcu_read_lock_bh();
>
> -       list_for_each_entry(sched, &ip_vs_schedulers, n_list) {
> +       list_for_each_entry_rcu(sched, &ip_vs_schedulers, n_list) {
>                /*
>                 * Test and get the modules atomically
>                 */
> @@ -105,14 +105,14 @@ static struct ip_vs_scheduler *ip_vs_sch
>                }
>                if (strcmp(sched_name, sched->name)==0) {
>                        /* HIT */
> -                       read_unlock_bh(&__ip_vs_sched_lock);
> +                       rcu_read_unlock_bh();
>                        return sched;
>                }
>                if (sched->module)
>                        module_put(sched->module);
>        }
>
> -       read_unlock_bh(&__ip_vs_sched_lock);
> +       rcu_read_unlock_bh();
>        return NULL;
>  }
>
> @@ -167,10 +167,10 @@ int register_ip_vs_scheduler(struct ip_v
>        /* increase the module use count */
>        ip_vs_use_count_inc();
>
> -       write_lock_bh(&__ip_vs_sched_lock);
> +       spin_lock_bh(&ip_vs_sched_mutex);
>
>        if (!list_empty(&scheduler->n_list)) {
> -               write_unlock_bh(&__ip_vs_sched_lock);
> +               spin_unlock_bh(&ip_vs_sched_mutex);
>                ip_vs_use_count_dec();
>                pr_err("%s(): [%s] scheduler already linked\n",
>                       __func__, scheduler->name);
> @@ -181,9 +181,9 @@ int register_ip_vs_scheduler(struct ip_v
>         *  Make sure that the scheduler with this name doesn't exist
>         *  in the scheduler list.
>         */
> -       list_for_each_entry(sched, &ip_vs_schedulers, n_list) {
> +       list_for_each_entry_rcu(sched, &ip_vs_schedulers, n_list) {
>                if (strcmp(scheduler->name, sched->name) == 0) {
> -                       write_unlock_bh(&__ip_vs_sched_lock);
> +                       spin_unlock_bh(&ip_vs_sched_mutex);
>                        ip_vs_use_count_dec();
>                        pr_err("%s(): [%s] scheduler already existed "
>                               "in the system\n", __func__, scheduler->name);
> @@ -193,8 +193,8 @@ int register_ip_vs_scheduler(struct ip_v
>        /*
>         *      Add it into the d-linked scheduler list
>         */
> -       list_add(&scheduler->n_list, &ip_vs_schedulers);
> -       write_unlock_bh(&__ip_vs_sched_lock);
> +       list_add_rcu(&scheduler->n_list, &ip_vs_schedulers);
> +       spin_unlock_bh(&ip_vs_sched_mutex);
>
>        pr_info("[%s] scheduler registered.\n", scheduler->name);
>
> @@ -212,9 +212,9 @@ int unregister_ip_vs_scheduler(struct ip
>                return -EINVAL;
>        }
>
> -       write_lock_bh(&__ip_vs_sched_lock);
> +       spin_lock_bh(&ip_vs_sched_mutex);
>        if (list_empty(&scheduler->n_list)) {
> -               write_unlock_bh(&__ip_vs_sched_lock);
> +               spin_unlock_bh(&ip_vs_sched_mutex);
>                pr_err("%s(): [%s] scheduler is not in the list. failed\n",
>                       __func__, scheduler->name);
>                return -EINVAL;
> @@ -223,8 +223,8 @@ int unregister_ip_vs_scheduler(struct ip
>        /*
>         *      Remove it from the d-linked scheduler list
>         */
> -       list_del(&scheduler->n_list);
> -       write_unlock_bh(&__ip_vs_sched_lock);
> +       list_del_rcu(&scheduler->n_list);
> +       spin_unlock_bh(&ip_vs_sched_mutex);

Need a rcu_barrier_bh().

>
>        /* decrease the module use count */
>        ip_vs_use_count_dec();



-- 
Regards,
Changli Gao(xiaosuo@...il.com)
--
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