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Date: Tue, 4 Sep 2012 16:53:06 +0200
From: Daniel Borkmann <danborkmann@...earbox.net>
To: Iulius Curt <iulius.curt@...il.com>
Cc: davem@...emloft.net, edumazet@...gle.com, xemul@...allels.com,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
dbaluta@...acom.com, Iulius Curt <icurt@...acom.com>,
Sorin Dumitru <sdumitru@...acom.com>
Subject: Re: [RFC] packet: change call of synchronize_net to call_rcu
On Tue, Sep 4, 2012 at 4:16 PM, Iulius Curt <iulius.curt@...il.com> wrote:
> synchronize_net is called every time we close a PF_PACKET socket which is
> causing performance loss when doing this on many sockets.
Do you have any particular use case in mind? I can imagine if you are
closing a PF_PACKET socket in a network analyzer application, you're
more or less out of its 'critical path' anyway.
> Signed-off-by: Sorin Dumitru <sdumitru@...acom.com>
> Signed-off-by: Iulius Curt <icurt@...acom.com>
> ---
> Statistics using test program [1]
>
> Sockets count | Not patched | Patched
> _________________________________________
> 1 000 000 | 1.28 s | 1.22 s
> 5 000 000 | 7.3 s | 6.25 s
> 50 000 000 | 72.89 s | 64.41 s
>
> [1] http://pastebin.com/xQ9BziaP
> ---
> net/packet/af_packet.c | 46 ++++++++++++++++++++++++++++++++++++----------
> net/packet/internal.h | 1 +
> 2 files changed, 37 insertions(+), 10 deletions(-)
>
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index 5dafe84..7b60135 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -2299,6 +2299,32 @@ static int packet_sendmsg(struct kiocb *iocb, struct socket *sock,
> return packet_snd(sock, msg, len);
> }
>
> +void packet_release_finish(struct sock *sk, int null)
> +{
> + struct socket *sock = sk->sk_socket;
> +
> + sock_orphan(sk);
> + /* Modifing this after the socket has been released
> + * might lead to memory corruption so we don't do it */
> + if (null)
> + sock->sk = NULL;
One minor remark: please don't name this variable "null" since it can
have a value of 0 or 1 in your code, it's a bit misleading. Maybe
rather "nullify" or something.
> + /* Purge queues */
> +
> + skb_queue_purge(&sk->sk_receive_queue);
> + sk_refcnt_debug_release(sk);
> +
> + sock_put(sk);
> +}
> +
> +void packet_release_rcu(struct rcu_head *rcu)
> +{
> + struct packet_sock *po = container_of(rcu, struct packet_sock, rcu_head);
> + struct sock *sk = &po->sk;
> +
> + packet_release_finish(sk, 0);
> +}
> +
> /*
> * Close a PACKET socket. This is fairly simple. We immediately go
> * to 'closed' state and remove our protocol entry in the device list.
> @@ -2310,6 +2336,7 @@ static int packet_release(struct socket *sock)
> struct packet_sock *po;
> struct net *net;
> union tpacket_req_u req_u;
> + int postpone = 0;
>
> if (!sk)
> return 0;
> @@ -2326,7 +2353,10 @@ static int packet_release(struct socket *sock)
> preempt_enable();
>
> spin_lock(&po->bind_lock);
> - unregister_prot_hook(sk, false);
> + if (po->running) {
> + postpone = 1;
> + __unregister_prot_hook(sk, false);
> + }
> if (po->prot_hook.dev) {
> dev_put(po->prot_hook.dev);
> po->prot_hook.dev = NULL;
> @@ -2345,19 +2375,15 @@ static int packet_release(struct socket *sock)
>
> fanout_release(sk);
>
> - synchronize_net();
> /*
> * Now the socket is dead. No more input will appear.
> */
> - sock_orphan(sk);
> - sock->sk = NULL;
> -
> - /* Purge queues */
> -
> - skb_queue_purge(&sk->sk_receive_queue);
> - sk_refcnt_debug_release(sk);
> + if (postpone) {
> + call_rcu(&po->rcu_head, packet_release_rcu);
> + return 0;
> + }
>
> - sock_put(sk);
> + packet_release_finish(sk, 1);
> return 0;
> }
>
> diff --git a/net/packet/internal.h b/net/packet/internal.h
> index 44945f6..5778c12 100644
> --- a/net/packet/internal.h
> +++ b/net/packet/internal.h
> @@ -104,6 +104,7 @@ struct packet_sock {
> int ifindex; /* bound device */
> __be16 num;
> struct packet_mclist *mclist;
> + struct rcu_head rcu_head;
> atomic_t mapped;
> enum tpacket_versions tp_version;
> unsigned int tp_hdrlen;
> --
> 1.7.9.5
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