[PATCH net-next v3 0/3] pf_packet updates

[PATCH net-next v3 0/3] pf_packet updates

[Daniel Borkmann]

Changelog:

v1->v2:
 - put assignments under bind lock in patch 1
 - added 2 more relevant patches

v2->v3:
 - made refcnt unsigned in patch 3
 - rest unchanged

Thanks !

Daniel Borkmann (3):
  packet: improve socket create/bind latency in some cases
  packet: don't unconditionally schedule() in case of MSG_DONTWAIT
  packet: use percpu mmap tx frame pending refcount

 net/packet/af_packet.c | 106 +++++++++++++++++++++++++++++++++++++++----------
 net/packet/diag.c      |   1 +
 net/packet/internal.h  |   2 +-
 3 files changed, 87 insertions(+), 22 deletions(-)

-- 
1.7.11.7

[PATCH net-next v3 1/3] packet: improve socket create/bind latency in some cases

[Daniel Borkmann]

Most people acquire PF_PACKET sockets with a protocol argument in
the socket call, e.g. libpcap does so with htons(ETH_P_ALL) for
all its sockets. Most likely, at some point in time a subsequent
bind() call will follow, e.g. in libpcap with ...

  memset(&sll, 0, sizeof(sll));
  sll.sll_family          = AF_PACKET;
  sll.sll_ifindex         = ifindex;
  sll.sll_protocol        = htons(ETH_P_ALL);

... as arguments. What happens in the kernel is that already
in socket() syscall, we install a proto hook via register_prot_hook()
if our protocol argument is != 0. Yet, in bind() we're almost
doing the same work by doing a unregister_prot_hook() with an
expensive synchronize_net() call in case during socket() the proto
was != 0, plus follow-up register_prot_hook() with a bound device
to it this time, in order to limit traffic we get.

In the case when the protocol and user supplied device index (== 0)
does not change from socket() to bind(), we can spare us doing
the same work twice. Similarly for re-binding to the same device
and protocol. For these scenarios, we can decrease create/bind
latency from ~7447us (sock-bind-2 case) to ~89us (sock-bind-1 case)
with this patch.

Alternatively, for the first case, if people care, they should
simply create their sockets with proto == 0 argument and define
the protocol during bind() as this saves a call to synchronize_net()
as well (sock-bind-3 case).

In all other cases, we're tied to user space behaviour we must not
change, also since a bind() is not strictly required. Thus, we need
the synchronize_net() to make sure no asynchronous packet processing
paths still refer to the previous elements of po->prot_hook.

In case of mmap()ed sockets, the workflow that includes bind() is
socket() -> setsockopt(<ring>) -> bind(). In that case, a pair of
{__unregister, register}_prot_hook is being called from setsockopt()
in order to install the new protocol receive handler. Thus, when
we call bind and can skip a re-hook, we have already previously
installed the new handler. For fanout, this is handled different
entirely, so we should be good.

Timings on an i7-3520M machine:

  * sock-bind-1:   89 us
  * sock-bind-2: 7447 us
  * sock-bind-3:   75 us

sock-bind-1:
  socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP)) = 3
  bind(3, {sa_family=AF_PACKET, proto=htons(ETH_P_IP), if=all(0),
           pkttype=PACKET_HOST, addr(0)={0, }, 20) = 0

sock-bind-2:
  socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP)) = 3
  bind(3, {sa_family=AF_PACKET, proto=htons(ETH_P_IP), if=lo(1),
           pkttype=PACKET_HOST, addr(0)={0, }, 20) = 0

sock-bind-3:
  socket(PF_PACKET, SOCK_RAW, 0) = 3
  bind(3, {sa_family=AF_PACKET, proto=htons(ETH_P_IP), if=lo(1),
           pkttype=PACKET_HOST, addr(0)={0, }, 20) = 0

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
---
 net/packet/af_packet.c | 33 ++++++++++++++++++++++-----------
 1 file changed, 22 insertions(+), 11 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 279467b..85bb38c 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2567,9 +2567,12 @@ static int packet_release(struct socket *sock)
  *	Attach a packet hook.
  */
 
-static int packet_do_bind(struct sock *sk, struct net_device *dev, __be16 protocol)
+static int packet_do_bind(struct sock *sk, struct net_device *dev, __be16 proto)
 {
 	struct packet_sock *po = pkt_sk(sk);
+	const struct net_device *dev_curr;
+	__be16 proto_curr;
+	bool need_rehook;
 
 	if (po->fanout) {
 		if (dev)
@@ -2579,21 +2582,29 @@ static int packet_do_bind(struct sock *sk, struct net_device *dev, __be16 protoc
 	}
 
 	lock_sock(sk);
-
 	spin_lock(&po->bind_lock);
-	unregister_prot_hook(sk, true);
 
-	po->num = protocol;
-	po->prot_hook.type = protocol;
-	if (po->prot_hook.dev)
-		dev_put(po->prot_hook.dev);
+	proto_curr = po->prot_hook.type;
+	dev_curr = po->prot_hook.dev;
+
+	need_rehook = proto_curr != proto || dev_curr != dev;
+
+	if (need_rehook) {
+		unregister_prot_hook(sk, true);
 
-	po->prot_hook.dev = dev;
-	po->ifindex = dev ? dev->ifindex : 0;
+		po->num = proto;
+		po->prot_hook.type = proto;
+
+		if (po->prot_hook.dev)
+			dev_put(po->prot_hook.dev);
 
-	packet_cached_dev_assign(po, dev);
+		po->prot_hook.dev = dev;
+
+		po->ifindex = dev ? dev->ifindex : 0;
+		packet_cached_dev_assign(po, dev);
+	}
 
-	if (protocol == 0)
+	if (proto == 0 || !need_rehook)
 		goto out_unlock;
 
 	if (!dev || (dev->flags & IFF_UP)) {
-- 
1.7.11.7

[PATCH net-next v3 2/3] packet: don't unconditionally schedule() in case of MSG_DONTWAIT

[Daniel Borkmann]

In tpacket_snd(), when we've discovered a first frame that is
not in status TP_STATUS_SEND_REQUEST, and return a NULL buffer,
we exit the send routine in case of MSG_DONTWAIT, since we've
finished traversing the mmaped send ring buffer and don't care
about pending frames.

While doing so, we still unconditionally call an expensive
schedule() in the packet_current_frame() "error" path, which
is unnecessary in this case since it's enough to just quit
the function.

Also, in case MSG_DONTWAIT is not set, we should rather test
for need_resched() first and do schedule() only if necessary
since meanwhile pending frames could already have finished
processing and called skb destructor.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
---
 net/packet/af_packet.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 85bb38c..d5495d8 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2156,6 +2156,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
 	int err, reserve = 0;
 	void *ph;
 	struct sockaddr_ll *saddr = (struct sockaddr_ll *)msg->msg_name;
+	bool need_wait = !(msg->msg_flags & MSG_DONTWAIT);
 	int tp_len, size_max;
 	unsigned char *addr;
 	int len_sum = 0;
@@ -2198,10 +2199,10 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
 
 	do {
 		ph = packet_current_frame(po, &po->tx_ring,
-				TP_STATUS_SEND_REQUEST);
-
+					  TP_STATUS_SEND_REQUEST);
 		if (unlikely(ph == NULL)) {
-			schedule();
+			if (need_wait && need_resched())
+				schedule();
 			continue;
 		}
 
@@ -2255,10 +2256,8 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
 		}
 		packet_increment_head(&po->tx_ring);
 		len_sum += tp_len;
-	} while (likely((ph != NULL) ||
-			((!(msg->msg_flags & MSG_DONTWAIT)) &&
-			 (atomic_read(&po->tx_ring.pending))))
-		);
+	} while (likely((ph != NULL) || (need_wait &&
+					 atomic_read(&po->tx_ring.pending))));
 
 	err = len_sum;
 	goto out_put;
-- 
1.7.11.7

[PATCH net-next v3 3/3] packet: use percpu mmap tx frame pending refcount

[Daniel Borkmann]

In PF_PACKET's packet mmap(), we can avoid using one atomic_inc()
and one atomic_dec() call in skb destructor and use a percpu
reference count instead in order to determine if packets are
still pending to be sent out. Micro-benchmark with [1] that has
been slightly modified (that is, protcol = 0 in socket(2) and
bind(2)), example on a rather crappy testing machine; I expect
it to scale and have even better results on bigger machines:

./packet_mm_tx -s7000 -m7200 -z700000 em1, avg over 2500 runs:

With patch:    4,022,015 cyc
Without patch: 4,812,994 cyc

time ./packet_mm_tx -s64 -c10000000 em1 > /dev/null, stable:

With patch:
  real         1m32.241s
  user         0m0.287s
  sys          1m29.316s

Without patch:
  real         1m38.386s
  user         0m0.265s
  sys          1m35.572s

In function tpacket_snd(), it is okay to use packet_read_pending()
since in fast-path we short-circuit the condition already with
ph != NULL, since we have next frames to process. In case we have
MSG_DONTWAIT, we also do not execute this path as need_wait is
false here anyway, and in case of _no_ MSG_DONTWAIT flag, it is
okay to call a packet_read_pending(), because when we ever reach
that path, we're done processing outgoing frames anyway and only
look if there are skbs still outstanding to be orphaned. We can
stay lockless in this percpu counter since it's acceptable when we
reach this path for the sum to be imprecise first, but we'll level
out at 0 after all pending frames have reached the skb destructor
eventually through tx reclaim. When people pin a tx process to
particular CPUs, we expect overflows to happen in the reference
counter as on one CPU we expect heavy increase; and distributed
through ksoftirqd on all CPUs a decrease, for example. As
David Laight points out, since the C language doesn't define the
result of signed int overflow (i.e. rather than wrap, it is
allowed to saturate as a possible outcome), we have to use
unsigned int as reference count. The sum over all CPUs when tx
is complete will result in 0 again.

The BUG_ON() in tpacket_destruct_skb() we can remove as well. It
can _only_ be set from inside tpacket_snd() path and we made sure
to increase tx_ring.pending in any case before we called po->xmit(skb).
So testing for tx_ring.pending == 0 is not too useful. Instead, it
would rather have been useful to test if lower layers didn't orphan
the skb so that we're missing ring slots being put back to
TP_STATUS_AVAILABLE. But such a bug will be caught in user space
already as we end up realizing that we do not have any
TP_STATUS_AVAILABLE slots left anymore. Therefore, we're all set.

Btw, in case of RX_RING path, we do not make use of the pending
member, therefore we also don't need to use up any percpu memory
here. Also note that __alloc_percpu() already returns a zero-filled
percpu area, so initialization is done already.

  [1] http://wiki.ipxwarzone.com/index.php5?title=Linux_packet_mmap

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
---
 net/packet/af_packet.c | 66 +++++++++++++++++++++++++++++++++++++++++++++-----
 net/packet/diag.c      |  1 +
 net/packet/internal.h  |  2 +-
 3 files changed, 62 insertions(+), 7 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index d5495d8..12f2f72 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -89,6 +89,7 @@
 #include <linux/errqueue.h>
 #include <linux/net_tstamp.h>
 #include <linux/reciprocal_div.h>
+#include <linux/percpu.h>
 #ifdef CONFIG_INET
 #include <net/inet_common.h>
 #endif
@@ -1168,6 +1169,47 @@ static void packet_increment_head(struct packet_ring_buffer *buff)
 	buff->head = buff->head != buff->frame_max ? buff->head+1 : 0;
 }
 
+static void packet_inc_pending(struct packet_ring_buffer *rb)
+{
+	this_cpu_inc(*rb->pending_refcnt);
+}
+
+static void packet_dec_pending(struct packet_ring_buffer *rb)
+{
+	this_cpu_dec(*rb->pending_refcnt);
+}
+
+static unsigned int packet_read_pending(const struct packet_ring_buffer *rb)
+{
+	unsigned int refcnt = 0;
+	int cpu;
+
+	/* We don't use pending refcount in rx_ring. */
+	if (rb->pending_refcnt == NULL)
+		return 0;
+
+	for_each_possible_cpu(cpu)
+		refcnt += *per_cpu_ptr(rb->pending_refcnt, cpu);
+
+	return refcnt;
+}
+
+static int packet_alloc_pending(struct packet_sock *po)
+{
+	po->rx_ring.pending_refcnt = NULL;
+
+	po->tx_ring.pending_refcnt = alloc_percpu(unsigned int);
+	if (unlikely(po->tx_ring.pending_refcnt == NULL))
+		return -ENOBUFS;
+
+	return 0;
+}
+
+static void packet_free_pending(struct packet_sock *po)
+{
+	free_percpu(po->tx_ring.pending_refcnt);
+}
+
 static bool packet_rcv_has_room(struct packet_sock *po, struct sk_buff *skb)
 {
 	struct sock *sk = &po->sk;
@@ -2014,8 +2056,7 @@ static void tpacket_destruct_skb(struct sk_buff *skb)
 		__u32 ts;
 
 		ph = skb_shinfo(skb)->destructor_arg;
-		BUG_ON(atomic_read(&po->tx_ring.pending) == 0);
-		atomic_dec(&po->tx_ring.pending);
+		packet_dec_pending(&po->tx_ring);
 
 		ts = __packet_set_timestamp(po, ph, skb);
 		__packet_set_status(po, ph, TP_STATUS_AVAILABLE | ts);
@@ -2236,7 +2277,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
 		skb_set_queue_mapping(skb, packet_pick_tx_queue(dev));
 		skb->destructor = tpacket_destruct_skb;
 		__packet_set_status(po, ph, TP_STATUS_SENDING);
-		atomic_inc(&po->tx_ring.pending);
+		packet_inc_pending(&po->tx_ring);
 
 		status = TP_STATUS_SEND_REQUEST;
 		err = po->xmit(skb);
@@ -2256,8 +2297,14 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
 		}
 		packet_increment_head(&po->tx_ring);
 		len_sum += tp_len;
-	} while (likely((ph != NULL) || (need_wait &&
-					 atomic_read(&po->tx_ring.pending))));
+	} while (likely((ph != NULL) ||
+		/* Note: packet_read_pending() might be slow if we have
+		 * to call it as it's per_cpu variable, but in fast-path
+		 * we already short-circuit the loop with the first
+		 * condition, and luckily don't have to go that path
+		 * anyway.
+		 */
+		 (need_wait && packet_read_pending(&po->tx_ring))));
 
 	err = len_sum;
 	goto out_put;
@@ -2556,6 +2603,7 @@ static int packet_release(struct socket *sock)
 	/* Purge queues */
 
 	skb_queue_purge(&sk->sk_receive_queue);
+	packet_free_pending(po);
 	sk_refcnt_debug_release(sk);
 
 	sock_put(sk);
@@ -2717,6 +2765,10 @@ static int packet_create(struct net *net, struct socket *sock, int protocol,
 	po->num = proto;
 	po->xmit = dev_queue_xmit;
 
+	err = packet_alloc_pending(po);
+	if (err)
+		goto out2;
+
 	packet_cached_dev_reset(po);
 
 	sk->sk_destruct = packet_sock_destruct;
@@ -2749,6 +2801,8 @@ static int packet_create(struct net *net, struct socket *sock, int protocol,
 	preempt_enable();
 
 	return 0;
+out2:
+	sk_free(sk);
 out:
 	return err;
 }
@@ -3676,7 +3730,7 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u,
 	if (!closing) {
 		if (atomic_read(&po->mapped))
 			goto out;
-		if (atomic_read(&rb->pending))
+		if (packet_read_pending(rb))
 			goto out;
 	}
 
diff --git a/net/packet/diag.c b/net/packet/diag.c
index a9584a2..533ce4f 100644
--- a/net/packet/diag.c
+++ b/net/packet/diag.c
@@ -3,6 +3,7 @@
 #include <linux/net.h>
 #include <linux/netdevice.h>
 #include <linux/packet_diag.h>
+#include <linux/percpu.h>
 #include <net/net_namespace.h>
 #include <net/sock.h>
 
diff --git a/net/packet/internal.h b/net/packet/internal.h
index 0a87d7b..eb9580a 100644
--- a/net/packet/internal.h
+++ b/net/packet/internal.h
@@ -64,7 +64,7 @@ struct packet_ring_buffer {
 	unsigned int		pg_vec_pages;
 	unsigned int		pg_vec_len;
 
-	atomic_t		pending;
+	unsigned int __percpu	*pending_refcnt;
 
 	struct tpacket_kbdq_core	prb_bdqc;
 };
-- 
1.7.11.7

Re: [PATCH net-next v3 0/3] pf_packet updates

[David Miller]

From: Daniel Borkmann <dborkman@redhat.com>
Date: Wed, 15 Jan 2014 16:25:33 +0100

> Changelog:
> 
> v1->v2:
>  - put assignments under bind lock in patch 1
>  - added 2 more relevant patches
> 
> v2->v3:
>  - made refcnt unsigned in patch 3
>  - rest unchanged

Series applied, thanks Daniel.