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udp: scalability improvements

PATCH Superseded Paolo Abeni 3 participants 10 messages May 15, 2017 – Oct 25, 2018

Subsystems (4)
Networking Network drivers Sockets UDP

v1 of 2 Superseded Latest is v2 →

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Paolo Abeni

author maintainer
#0 lore raw

cover udp: scalability improvements

This patch series implement an idea suggested by Eric Dumazet to reduce the contention of the udp sk_receive_queue lock when the socket is under flood.

An ancillary queue is added to the udp socket, and the socket always tries first to read packets from such queue. If it's empty, we splice the content from sk_receive_queue into the ancillary queue.

The first patch introduces some helpers to keep the udp code small, and the following two implement the ancillary queue strategy. The code is split to hopefully help the reviewing process.

The measured overall gain under udp flood is up to the 30% depending on the numa layout and the number of ingress queue used by the relevant nic.

The performance numbers have been gathered using pktgen as sender, with 64 bytes packets, random src port on a host b2b connected via a 10Gbs link with the dut.

The receiver used the udp_sink program by Jesper [1] and an h/w l4 rx hash on the ingress nic, so that the number of ingress nic rx queues hit by the udp traffic could be controlled via ethtool -L.

The udp_sink program was bound to the first idle cpu, to get more stable numbers.

On a single numa node receiver:

nic rx queues           vanilla                 patched kernel
1                       1820 kpps               1900 kpps
2                       1950 kpps               2500 kpps
16                      1670 kpps               2120 kpps

When using a single nic rx queue, busy polling was also enabled, elsewhere, in the above scenario, the bh processing becomes the bottle-neck and this produces large artifacts in the measured performances (e.g. improving the udp sink run time, decreases the overall tput, since more action from the scheduler comes into play).

[1] https://github.com/netoptimizer/network-testing/blob/master/src/udp_sink.c

No changes since the RFC.

Paolo Abeni (3):
net/sock: factor out dequeue/peek with offset code
udp: use a separate rx queue for packet reception
udp: keep the sk_receive_queue held when splicing

 include/linux/skbuff.h |   7 +++
 include/linux/udp.h    |   3 +
 include/net/sock.h     |   4 +-
 include/net/udp.h      |   9 +--
 include/net/udplite.h  |   2 +-
 net/core/datagram.c    |  90 +++++++++++++++------------
 net/ipv4/udp.c         | 162 +++++++++++++++++++++++++++++++++++++++++++------
 net/ipv6/udp.c         |   3 +-
 8 files changed, 211 insertions(+), 69 deletions(-)
Signature · 1 line
2.9.3
author maintainer
#1 lore raw

PATCH 1/3 net/sock: factor out dequeue/peek with offset code

And update __sk_queue_drop_skb() to work on the specified queue. This will help the udp protocol to use an additional private rx queue in a later patch.

Signed-off-by Paolo Abeni <[email protected]>
---
 include/linux/skbuff.h |  7 ++++
 include/net/sock.h     |  4 +--
 net/core/datagram.c    | 90 ++++++++++++++++++++++++++++----------------------
 3 files changed, 60 insertions(+), 41 deletions(-)
include/linux/skbuff.h +7 -0
index a098d95..bfc7892 100644
@@ -3056,6 +3056,13 @@ static inline void skb_frag_list_init(struct sk_buff *skb)
 
 int __skb_wait_for_more_packets(struct sock *sk, int *err, long *timeo_p,
 				const struct sk_buff *skb);
+struct sk_buff *__skb_try_recv_from_queue(struct sock *sk,
+					  struct sk_buff_head *queue,
+					  unsigned int flags,
+					  void (*destructor)(struct sock *sk,
+							   struct sk_buff *skb),
+					  int *peeked, int *off, int *err,
+					  struct sk_buff **last);
 struct sk_buff *__skb_try_recv_datagram(struct sock *sk, unsigned flags,
 					void (*destructor)(struct sock *sk,
 							   struct sk_buff *skb),
include/net/sock.h +2 -2
index 66349e4..49d226f 100644
@@ -2035,8 +2035,8 @@ void sk_reset_timer(struct sock *sk, struct timer_list *timer,
 
 void sk_stop_timer(struct sock *sk, struct timer_list *timer);
 
-int __sk_queue_drop_skb(struct sock *sk, struct sk_buff *skb,
-			unsigned int flags,
+int __sk_queue_drop_skb(struct sock *sk, struct sk_buff_head *sk_queue,
+			struct sk_buff *skb, unsigned int flags,
 			void (*destructor)(struct sock *sk,
 					   struct sk_buff *skb));
 int __sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb);
net/core/datagram.c +51 -39

133 lines not on this page · raw message

Signature · 1 line
2.9.3
#3 lore raw

Re: [PATCH net-next 1/3] net/sock: factor out dequeue/peek with offset code

In reply to Paolo Abeni
Quoted 53 lines · Paolo Abeni

And update __sk_queue_drop_skb() to work on the specified queue. This will help the udp protocol to use an additional private rx queue in a later patch.

Signed-off-by Paolo Abeni <[email protected]>
---
 include/linux/skbuff.h |  7 ++++
 include/net/sock.h     |  4 +--
 net/core/datagram.c    | 90 ++++++++++++++++++++++++++++----------------------
 3 files changed, 60 insertions(+), 41 deletions(-)
include/linux/skbuff.h +7 -0
index a098d95..bfc7892 100644
@@ -3056,6 +3056,13 @@ static inline void skb_frag_list_init(struct sk_buff *skb)
 
 int __skb_wait_for_more_packets(struct sock *sk, int *err, long *timeo_p,
 				const struct sk_buff *skb);
+struct sk_buff *__skb_try_recv_from_queue(struct sock *sk,
+					  struct sk_buff_head *queue,
+					  unsigned int flags,
+					  void (*destructor)(struct sock *sk,
+							   struct sk_buff *skb),
+					  int *peeked, int *off, int *err,
+					  struct sk_buff **last);
 struct sk_buff *__skb_try_recv_datagram(struct sock *sk, unsigned flags,
 					void (*destructor)(struct sock *sk,
 							   struct sk_buff *skb),
include/net/sock.h +2 -2
index 66349e4..49d226f 100644
@@ -2035,8 +2035,8 @@ void sk_reset_timer(struct sock *sk, struct timer_list *timer,
 
 void sk_stop_timer(struct sock *sk, struct timer_list *timer);
 
-int __sk_queue_drop_skb(struct sock *sk, struct sk_buff *skb,
-			unsigned int flags,
+int __sk_queue_drop_skb(struct sock *sk, struct sk_buff_head *sk_queue,
+			struct sk_buff *skb, unsigned int flags,
 			void (*destructor)(struct sock *sk,
 					   struct sk_buff *skb));
 int __sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb);
net/core/datagram.c +1 -0
index db1866f2..a4592b4 100644
@@ -161,6 +161,43 @@ static struct sk_buff *skb_set_peeked(struct sk_buff *skb)
 	return skb;
 }
 
+struct sk_buff *__skb_try_recv_from_queue(struct sock *sk,

net/core/datagram.c static struct sk_buff *skb_set_peeked(struct sk_buff *skb) · line 174

Quoted 10 lines
net/core/datagram.c +10 -0
+					  struct sk_buff_head *queue,
+					  unsigned int flags,
+					  void (*destructor)(struct sock *sk,
+							   struct sk_buff *skb),
+					  int *peeked, int *off, int *err,
+					  struct sk_buff **last)
+{
+	struct sk_buff *skb;
+
+	*last = queue->prev;

this refactoring changed the behavior.
Now queue->prev is returned as last.
Whereas it was *last = queue before.

net/core/datagram.c static struct sk_buff *skb_set_peeked(struct sk_buff *skb) · line 175

Quoted 1 line
net/core/datagram.c +1 -0
+	skb_queue_walk(queue, skb) {

and *last = skb assignment is gone too.

Was this intentional ? Is this the right behavior?

Quoted 125 lines
net/core/datagram.c +39 -39
+		if (flags & MSG_PEEK) {
+			if (*off >= skb->len && (skb->len || *off ||
+						 skb->peeked)) {
+				*off -= skb->len;
+				continue;
+			}
+			if (!skb->len) {
+				skb = skb_set_peeked(skb);
+				if (unlikely(IS_ERR(skb))) {
+					*err = PTR_ERR(skb);
+					return skb;
+				}
+			}
+			*peeked = 1;
+			atomic_inc(&skb->users);
+		} else {
+			__skb_unlink(skb, queue);
+			if (destructor)
+				destructor(sk, skb);
+		}
+		return skb;
+	}
+	return NULL;
+}
+
 /**
  *	__skb_try_recv_datagram - Receive a datagram skbuff
  *	@sk: socket

@@ -216,46 +253,20 @@ struct sk_buff *__skb_try_recv_datagram(struct sock *sk, unsigned int flags,
 
 	*peeked = 0;
 	do {
+		int _off = *off;
+
 		/* Again only user level code calls this function, so nothing
 		 * interrupt level will suddenly eat the receive_queue.
 		 *
 		 * Look at current nfs client by the way...
 		 * However, this function was correct in any case. 8)
 		 */
-		int _off = *off;
-
-		*last = (struct sk_buff *)queue;
 		spin_lock_irqsave(&queue->lock, cpu_flags);
-		skb_queue_walk(queue, skb) {
-			*last = skb;
-			if (flags & MSG_PEEK) {
-				if (_off >= skb->len && (skb->len || _off ||
-							 skb->peeked)) {
-					_off -= skb->len;
-					continue;
-				}
-				if (!skb->len) {
-					skb = skb_set_peeked(skb);
-					if (IS_ERR(skb)) {
-						error = PTR_ERR(skb);
-						spin_unlock_irqrestore(&queue->lock,
-								       cpu_flags);
-						goto no_packet;
-					}
-				}
-				*peeked = 1;
-				atomic_inc(&skb->users);
-			} else {
-				__skb_unlink(skb, queue);
-				if (destructor)
-					destructor(sk, skb);
-			}
-			spin_unlock_irqrestore(&queue->lock, cpu_flags);
-			*off = _off;
-			return skb;
-		}
-
+		skb = __skb_try_recv_from_queue(sk, queue, flags, destructor,
+						peeked, &_off, err, last);
 		spin_unlock_irqrestore(&queue->lock, cpu_flags);
+		if (skb)
+			return skb;
 
 		if (!sk_can_busy_loop(sk))
 			break;

@@ -335,8 +346,8 @@ void __skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb, int len)
 }
 EXPORT_SYMBOL(__skb_free_datagram_locked);
 
-int __sk_queue_drop_skb(struct sock *sk, struct sk_buff *skb,
-			unsigned int flags,
+int __sk_queue_drop_skb(struct sock *sk, struct sk_buff_head *sk_queue,
+			struct sk_buff *skb, unsigned int flags,
 			void (*destructor)(struct sock *sk,
 					   struct sk_buff *skb))
 {

@@ -344,15 +355,15 @@ int __sk_queue_drop_skb(struct sock *sk, struct sk_buff *skb,
 
 	if (flags & MSG_PEEK) {
 		err = -ENOENT;
-		spin_lock_bh(&sk->sk_receive_queue.lock);
-		if (skb == skb_peek(&sk->sk_receive_queue)) {
-			__skb_unlink(skb, &sk->sk_receive_queue);
+		spin_lock_bh(&sk_queue->lock);
+		if (skb == skb_peek(sk_queue)) {
+			__skb_unlink(skb, sk_queue);
 			atomic_dec(&skb->users);
 			if (destructor)
 				destructor(sk, skb);
 			err = 0;
 		}
-		spin_unlock_bh(&sk->sk_receive_queue.lock);
+		spin_unlock_bh(&sk_queue->lock);
 	}
 
 	atomic_inc(&sk->sk_drops);

@@ -383,7 +394,8 @@ EXPORT_SYMBOL(__sk_queue_drop_skb);
 
 int skb_kill_datagram(struct sock *sk, struct sk_buff *skb, unsigned int flags)
 {
-	int err = __sk_queue_drop_skb(sk, skb, flags, NULL);
+	int err = __sk_queue_drop_skb(sk, &sk->sk_receive_queue, skb, flags,
+				      NULL);
 
 	kfree_skb(skb);
 	sk_mem_reclaim_partial(sk);
Signature · 1 line
2.9.3
author maintainer
#4 lore raw

Re: [PATCH net-next 1/3] net/sock: factor out dequeue/peek with offset code

Hi,

Quoted 69 lines · Alexei Starovoitov
Quoted 53 lines · Paolo Abeni

And update __sk_queue_drop_skb() to work on the specified queue. This will help the udp protocol to use an additional private rx queue in a later patch.

Signed-off-by Paolo Abeni <[email protected]>
---
 include/linux/skbuff.h |  7 ++++
 include/net/sock.h     |  4 +--
 net/core/datagram.c    | 90 ++++++++++++++++++++++++++++----------------------
 3 files changed, 60 insertions(+), 41 deletions(-)
include/linux/skbuff.h +7 -0
index a098d95..bfc7892 100644
@@ -3056,6 +3056,13 @@ static inline void skb_frag_list_init(struct sk_buff *skb)
 
 int __skb_wait_for_more_packets(struct sock *sk, int *err, long *timeo_p,
 				const struct sk_buff *skb);
+struct sk_buff *__skb_try_recv_from_queue(struct sock *sk,
+					  struct sk_buff_head *queue,
+					  unsigned int flags,
+					  void (*destructor)(struct sock *sk,
+							   struct sk_buff *skb),
+					  int *peeked, int *off, int *err,
+					  struct sk_buff **last);
 struct sk_buff *__skb_try_recv_datagram(struct sock *sk, unsigned flags,
 					void (*destructor)(struct sock *sk,
 							   struct sk_buff *skb),
include/net/sock.h +2 -2
index 66349e4..49d226f 100644
@@ -2035,8 +2035,8 @@ void sk_reset_timer(struct sock *sk, struct timer_list *timer,
 
 void sk_stop_timer(struct sock *sk, struct timer_list *timer);
 
-int __sk_queue_drop_skb(struct sock *sk, struct sk_buff *skb,
-			unsigned int flags,
+int __sk_queue_drop_skb(struct sock *sk, struct sk_buff_head *sk_queue,
+			struct sk_buff *skb, unsigned int flags,
 			void (*destructor)(struct sock *sk,
 					   struct sk_buff *skb));
 int __sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb);
net/core/datagram.c +1 -0
index db1866f2..a4592b4 100644
@@ -161,6 +161,43 @@ static struct sk_buff *skb_set_peeked(struct sk_buff *skb)
 	return skb;
 }
 
+struct sk_buff *__skb_try_recv_from_queue(struct sock *sk,

net/core/datagram.c static struct sk_buff *skb_set_peeked(struct sk_buff *skb) · line 174

Quoted 10 lines
net/core/datagram.c +10 -0
+					  struct sk_buff_head *queue,
+					  unsigned int flags,
+					  void (*destructor)(struct sock *sk,
+							   struct sk_buff *skb),
+					  int *peeked, int *off, int *err,
+					  struct sk_buff **last)
+{
+	struct sk_buff *skb;
+
+	*last = queue->prev;

this refactoring changed the behavior.
Now queue->prev is returned as last.
Whereas it was *last = queue before.

Quoted 5 lines

net/core/datagram.c static struct sk_buff *skb_set_peeked(struct sk_buff *skb) · line 175

Quoted 1 line
net/core/datagram.c +1 -0
+	skb_queue_walk(queue, skb) {

and *last = skb assignment is gone too.

Was this intentional ?

Yes.

Quoted 1 line

Is this the right behavior?

I think so. queue->prev is the last skb in the queue. With the old
code, __skb_try_recv_datagram(), when returning NULL, used the
instructions you quoted to overall set 'last' to the last skb in the queue. We did not use 'last' elsewhere. So overall this just reduce the number of instructions inside the loop. (unless I'm missing something).

Are you experiencing any specific issues due to the mentioned commit?

Thanks,

Paolo

#5 lore raw

Re: [PATCH net-next 1/3] net/sock: factor out dequeue/peek with offset code

Quoted 80 lines · Paolo Abeni

Hi,

Quoted 69 lines · Alexei Starovoitov
Quoted 53 lines · Paolo Abeni

And update __sk_queue_drop_skb() to work on the specified queue. This will help the udp protocol to use an additional private rx queue in a later patch.

Signed-off-by Paolo Abeni <[email protected]>
---
 include/linux/skbuff.h |  7 ++++
 include/net/sock.h     |  4 +--
 net/core/datagram.c    | 90 ++++++++++++++++++++++++++++----------------------
 3 files changed, 60 insertions(+), 41 deletions(-)
include/linux/skbuff.h +7 -0
index a098d95..bfc7892 100644
@@ -3056,6 +3056,13 @@ static inline void skb_frag_list_init(struct sk_buff *skb)
 
 int __skb_wait_for_more_packets(struct sock *sk, int *err, long *timeo_p,
 				const struct sk_buff *skb);
+struct sk_buff *__skb_try_recv_from_queue(struct sock *sk,
+					  struct sk_buff_head *queue,
+					  unsigned int flags,
+					  void (*destructor)(struct sock *sk,
+							   struct sk_buff *skb),
+					  int *peeked, int *off, int *err,
+					  struct sk_buff **last);
 struct sk_buff *__skb_try_recv_datagram(struct sock *sk, unsigned flags,
 					void (*destructor)(struct sock *sk,
 							   struct sk_buff *skb),
include/net/sock.h +2 -2
index 66349e4..49d226f 100644
@@ -2035,8 +2035,8 @@ void sk_reset_timer(struct sock *sk, struct timer_list *timer,
 
 void sk_stop_timer(struct sock *sk, struct timer_list *timer);
 
-int __sk_queue_drop_skb(struct sock *sk, struct sk_buff *skb,
-			unsigned int flags,
+int __sk_queue_drop_skb(struct sock *sk, struct sk_buff_head *sk_queue,
+			struct sk_buff *skb, unsigned int flags,
 			void (*destructor)(struct sock *sk,
 					   struct sk_buff *skb));
 int __sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb);
net/core/datagram.c +1 -0
index db1866f2..a4592b4 100644
@@ -161,6 +161,43 @@ static struct sk_buff *skb_set_peeked(struct sk_buff *skb)
 	return skb;
 }
 
+struct sk_buff *__skb_try_recv_from_queue(struct sock *sk,

net/core/datagram.c static struct sk_buff *skb_set_peeked(struct sk_buff *skb) · line 174

Quoted 10 lines
net/core/datagram.c +10 -0
+					  struct sk_buff_head *queue,
+					  unsigned int flags,
+					  void (*destructor)(struct sock *sk,
+							   struct sk_buff *skb),
+					  int *peeked, int *off, int *err,
+					  struct sk_buff **last)
+{
+	struct sk_buff *skb;
+
+	*last = queue->prev;

this refactoring changed the behavior.
Now queue->prev is returned as last.
Whereas it was *last = queue before.

Quoted 5 lines

net/core/datagram.c static struct sk_buff *skb_set_peeked(struct sk_buff *skb) · line 175

Quoted 1 line
net/core/datagram.c +1 -0
+	skb_queue_walk(queue, skb) {

and *last = skb assignment is gone too.

Was this intentional ?

Yes.

Quoted 7 lines
Quoted 1 line

Is this the right behavior?

I think so. queue->prev is the last skb in the queue. With the old
code, __skb_try_recv_datagram(), when returning NULL, used the
instructions you quoted to overall set 'last' to the last skb in the queue. We did not use 'last' elsewhere. So overall this just reduce the number of instructions inside the loop. (unless I'm missing something).

Right. On the second glance it does appear to be correct.

Quoted 1 line

Are you experiencing any specific issues due to the mentioned commit?

yes.

Just like what Baoyou Xie reported https://lore.kernel.org/patchwork/patch/962802/
we're hitting infinite loop in __skb_recv_datagram() on 4.11 kernel. and different, but also buggy, behavior on the net-next.

In particular __skb_try_recv_datagram() returns immediately,
because skb_queue_empty() is true (sk->sk_receive_queue.next == &sk->sk_receive_queue)

But __skb_wait_for_more_packets() also returns immediately because if (sk->sk_receive_queue.prev != skb) is also true.

There is a link list corruption in sk_receive_queue.

list->next == list, but list->prev still points to valid skb. Before your commit we had
*last = queue;
and we had this infinite loop I described above. After your commit
*last = queue->next;
which assigns buggy pointer into *last, but that accidentally makes if (sk->sk_receive_queue.prev != skb) to be false and __skb_wait_for_more_packets() goes into schedule_timeout(). Eventually bad things happen too, but in the different spot.

The corruption is somehow related to netlink_recvmsg() just like in that Baoyou Xie report.

The typical stack trace is

__skb_wait_for_more_packets+0x64/0x140
? skb_gro_receive+0x310/0x310
__skb_recv_datagram+0x5c/0xa0
skb_recv_datagram+0x31/0x40
netlink_recvmsg+0x51/0x3c0
? sock_write_iter+0xf8/0x110
SYSC_recvfrom+0x116/0x190

We didn't figure out a way to reproduce it yet.
kasan didn't help.
The way netlink socket pushes skbs into sk_receive_queue and drains it all looks correct. We thought it could be MSG_PEAK related, but skb->users refcnting also looks correct.

If anyone have any ideas what things to try, I'm all ears.

author maintainer
#6 lore raw

PATCH 2/3 udp: use a separate rx queue for packet reception

In reply to Paolo Abeni

under udp flood the sk_receive_queue spinlock is heavily contended. This patch try to reduce the contention on such lock adding a second receive queue to the udp sockets; recvmsg() looks first in such queue and, only if empty, tries to fetch the data from sk_receive_queue. The latter is spliced into the newly added queue every time the receive path has to acquire the sk_receive_queue lock.

The accounting of forward allocated memory is still protected with the sk_receive_queue lock, so udp_rmem_release() needs to acquire both locks when the forward deficit is flushed.

On specific scenarios we can end up acquiring and releasing the sk_receive_queue lock multiple times; that will be covered by the next patch

Suggested-by Eric Dumazet <[email protected]>
Signed-off-by Paolo Abeni <[email protected]>
---
 include/linux/udp.h   |   3 ++
 include/net/udp.h     |   9 +---
 include/net/udplite.h |   2 +-
 net/ipv4/udp.c        | 138 ++++++++++++++++++++++++++++++++++++++++++++------
 net/ipv6/udp.c        |   3 +-
 5 files changed, 131 insertions(+), 24 deletions(-)
include/linux/udp.h +3 -0
index 6cb4061..eaea63b 100644
@@ -80,6 +80,9 @@ struct udp_sock {
 						struct sk_buff *skb,
 						int nhoff);
 
+	/* udp_recvmsg try to use this before splicing sk_receive_queue */
+	struct sk_buff_head	reader_queue ____cacheline_aligned_in_smp;
+
 	/* This field is dirtied by udp_recvmsg() */
 	int		forward_deficit;
 };
include/net/udp.h +2 -7
index 3391dbd..1468dbd 100644
@@ -249,13 +249,8 @@ void udp_destruct_sock(struct sock *sk);
 void skb_consume_udp(struct sock *sk, struct sk_buff *skb, int len);
 int __udp_enqueue_schedule_skb(struct sock *sk, struct sk_buff *skb);
 void udp_skb_destructor(struct sock *sk, struct sk_buff *skb);
-static inline struct sk_buff *
-__skb_recv_udp(struct sock *sk, unsigned int flags, int noblock, int *peeked,
-	       int *off, int *err)
-{
-	return __skb_recv_datagram(sk, flags | (noblock ? MSG_DONTWAIT : 0),
-				   udp_skb_destructor, peeked, off, err);
-}
+struct sk_buff *__skb_recv_udp(struct sock *sk, unsigned int flags,
+			       int noblock, int *peeked, int *off, int *err);
 static inline struct sk_buff *skb_recv_udp(struct sock *sk, unsigned int flags,
 					   int noblock, int *err)
 {
include/net/udplite.h +1 -1
index ea34052..b7a18f6 100644
@@ -26,8 +26,8 @@ static __inline__ int udplite_getfrag(void *from, char *to, int  offset,
 /* Designate sk as UDP-Lite socket */
 static inline int udplite_sk_init(struct sock *sk)
 {
+	udp_init_sock(sk);
 	udp_sk(sk)->pcflag = UDPLITE_BIT;
-	sk->sk_destruct = udp_destruct_sock;
 	return 0;
 }
net/ipv4/udp.c +123 -15

214 lines not on this page · raw message

net/ipv6/udp.c +2 -1
index 04862ab..f78fdf8 100644
@@ -455,7 +455,8 @@ int udpv6_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 	return err;
 
 csum_copy_err:
-	if (!__sk_queue_drop_skb(sk, skb, flags, udp_skb_destructor)) {
+	if (!__sk_queue_drop_skb(sk, &udp_sk(sk)->reader_queue, skb, flags,
+				 udp_skb_destructor)) {
 		if (is_udp4) {
 			UDP_INC_STATS(sock_net(sk),
 				      UDP_MIB_CSUMERRORS, is_udplite);
Signature · 1 line
2.9.3
Acked-by on v1 2/3
#7 lore raw

Re: [PATCH net-next 2/3] udp: use a separate rx queue for packet reception

Quoted 12 lines · Paolo Abeni

under udp flood the sk_receive_queue spinlock is heavily contended. This patch try to reduce the contention on such lock adding a second receive queue to the udp sockets; recvmsg() looks first in such queue and, only if empty, tries to fetch the data from sk_receive_queue. The latter is spliced into the newly added queue every time the receive path has to acquire the sk_receive_queue lock.

The accounting of forward allocated memory is still protected with the sk_receive_queue lock, so udp_rmem_release() needs to acquire both locks when the forward deficit is flushed.

Quoted 7 lines

On specific scenarios we can end up acquiring and releasing the sk_receive_queue lock multiple times; that will be covered by the next patch

Suggested-by Eric Dumazet <[email protected]>
Signed-off-by Paolo Abeni <[email protected]>

---

Very nice, thanks for working on this Paolo.

Acked-by Eric Dumazet <[email protected]>
author maintainer
#8 lore raw

PATCH 3/3 udp: keep the sk_receive_queue held when splicing

In reply to Paolo Abeni

On packet reception, when we are forced to splice the sk_receive_queue, we can keep the related lock held, so that we can avoid re-acquiring it, if fwd memory scheduling is required.

Signed-off-by Paolo Abeni <[email protected]>
---
 net/ipv4/udp.c | 36 ++++++++++++++++++++++++++----------
 1 file changed, 26 insertions(+), 10 deletions(-)
net/ipv4/udp.c +26 -10
index 492c76b..d698973 100644
@@ -1164,7 +1164,8 @@ int udp_sendpage(struct sock *sk, struct page *page, int offset,
 }
 
 /* fully reclaim rmem/fwd memory allocated for skb */
-static void udp_rmem_release(struct sock *sk, int size, int partial)
+static void udp_rmem_release(struct sock *sk, int size, int partial,
+			     int rx_queue_lock_held)
 {
 	struct udp_sock *up = udp_sk(sk);
 	struct sk_buff_head *sk_queue;

@@ -1181,9 +1182,13 @@ static void udp_rmem_release(struct sock *sk, int size, int partial)
 	}
 	up->forward_deficit = 0;
 
-	/* acquire the sk_receive_queue for fwd allocated memory scheduling */
+	/* acquire the sk_receive_queue for fwd allocated memory scheduling,
+	 * if the called don't held it already
+	 */
 	sk_queue = &sk->sk_receive_queue;
-	spin_lock(&sk_queue->lock);
+	if (!rx_queue_lock_held)
+		spin_lock(&sk_queue->lock);
+
 
 	sk->sk_forward_alloc += size;
 	amt = (sk->sk_forward_alloc - partial) & ~(SK_MEM_QUANTUM - 1);

@@ -1197,7 +1202,8 @@ static void udp_rmem_release(struct sock *sk, int size, int partial)
 	/* this can save us from acquiring the rx queue lock on next receive */
 	skb_queue_splice_tail_init(sk_queue, &up->reader_queue);
 
-	spin_unlock(&sk_queue->lock);
+	if (!rx_queue_lock_held)
+		spin_unlock(&sk_queue->lock);
 }
 
 /* Note: called with reader_queue.lock held.

@@ -1207,10 +1213,16 @@ static void udp_rmem_release(struct sock *sk, int size, int partial)
  */
 void udp_skb_destructor(struct sock *sk, struct sk_buff *skb)
 {
-	udp_rmem_release(sk, skb->dev_scratch, 1);
+	udp_rmem_release(sk, skb->dev_scratch, 1, 0);
 }
 EXPORT_SYMBOL(udp_skb_destructor);
 
+/* as above, but the caller held the rx queue lock, too */
+void udp_skb_dtor_locked(struct sock *sk, struct sk_buff *skb)
+{
+	udp_rmem_release(sk, skb->dev_scratch, 1, 1);
+}
+
 /* Idea of busylocks is to let producers grab an extra spinlock
  * to relieve pressure on the receive_queue spinlock shared by consumer.
  * Under flood, this means that only one producer can be in line

@@ -1325,7 +1337,7 @@ void udp_destruct_sock(struct sock *sk)
 		total += skb->truesize;
 		kfree_skb(skb);
 	}
-	udp_rmem_release(sk, total, 0);
+	udp_rmem_release(sk, total, 0, 1);
 
 	inet_sock_destruct(sk);
 }

@@ -1397,7 +1409,7 @@ static int first_packet_length(struct sock *sk)
 	}
 	res = skb ? skb->len : -1;
 	if (total)
-		udp_rmem_release(sk, total, 1);
+		udp_rmem_release(sk, total, 1, 0);
 	spin_unlock_bh(&rcvq->lock);
 	return res;
 }

@@ -1471,16 +1483,20 @@ struct sk_buff *__skb_recv_udp(struct sock *sk, unsigned int flags,
 				goto busy_check;
 			}
 
-			/* refill the reader queue and walk it again */
+			/* refill the reader queue and walk it again
+			 * keep both queues locked to avoid re-acquiring
+			 * the sk_receive_queue lock if fwd memory scheduling
+			 * is needed.
+			 */
 			_off = *off;
 			spin_lock(&sk_queue->lock);
 			skb_queue_splice_tail_init(sk_queue, queue);
-			spin_unlock(&sk_queue->lock);
 
 			skb = __skb_try_recv_from_queue(sk, queue, flags,
-							udp_skb_destructor,
+							udp_skb_dtor_locked,
 							peeked, &_off, err,
 							&last);
+			spin_unlock(&sk_queue->lock);
 			spin_unlock_bh(&queue->lock);
 			if (skb) {
 				*off = _off;
Signature · 1 line
2.9.3
#9 lore raw

Re: [PATCH net-next 3/3] udp: keep the sk_receive_queue held when splicing

Quoted 15 lines · Paolo Abeni

On packet reception, when we are forced to splice the sk_receive_queue, we can keep the related lock held, so that we can avoid re-acquiring it, if fwd memory scheduling is required.

Signed-off-by Paolo Abeni <[email protected]>
---
 net/ipv4/udp.c | 36 ++++++++++++++++++++++++++----------
 1 file changed, 26 insertions(+), 10 deletions(-)
net/ipv4/udp.c +0 -0
index 492c76b..d698973 100644

net/ipv4/udp.c int udp_sendpage(struct sock *sk, struct page *page, int offset, · line 1168

Quoted 6 lines
net/ipv4/udp.c +2 -1
@@ -1164,7 +1164,8 @@ int udp_sendpage(struct sock *sk, struct page *page, int offset,
 }
 
 /* fully reclaim rmem/fwd memory allocated for skb */
-static void udp_rmem_release(struct sock *sk, int size, int partial)
+static void udp_rmem_release(struct sock *sk, int size, int partial,
+			     int rx_queue_lock_held)

Looks good, but please use a bool rx_queue_lock_held ?

Thanks !