Subject: [PATCH RFC net-next 02/11] udp: add gso

From: Willem de Bruijn <[email-masked]>
Date: Tue, 17 Apr 2018 16:00:52 -0400

From: Willem de Bruijn <[email-masked]>

Implement generic segmentation offload for udp datagrams. Callers can
concatenate and send at once the payload of multiple datagrams with
the same destination.

To set segment size, the caller sets socket option UDP_SEGMENT to the
length of each discrete payload. This value must be smaller than or
equal to the relevant MTU.

A follow-up patch adds cmsg UDP_SEGMENT to specify segment size on a
per send call basis.

Total byte length may then exceed MTU. If not an exact multiple of
segment size, the last segment will be shorter.

UDP GSO is not UFO. UFO fragments a single large datagram. GSO splits
a large payload into a number of discrete UDP datagrams.

The implementation adds a GSO type SKB_UDP_GSO_L4 to differentiate it
from UFO (SKB_UDP_GSO). It adds a gso_size field to the udp socket,
ip(v6) cmsg cookie and inet_cork structure to be able to set the value
at setsockopt or cmsg time and to work with both lockless and corked
paths. A lockless-only cmsg-only patch would be significantly shorter.

The feature requires udp checksum offload to avoid checksumming in the
GSO layer. This is disabled with MSG_MORE as of commit d749c9cbffd6
("ipv4: no CHECKSUM_PARTIAL on MSG_MORE corked sockets") and commit
682b1a9d3f96 ("ipv6: no CHECKSUM_PARTIAL on MSG_MORE corked sockets"),
so only the lockless fast path works. IPPROTO_UDPLITE is excluded as
well, as that protocol has no gso handler registered.

Initial benchmark numbers show UDP GSO about as expensive as TCP GSO.

    tcp tso
     3197 MB/s 54232 msg/s 54232 calls/s
         6,457,754,262      cycles

    tcp gso
     1765 MB/s 29939 msg/s 29939 calls/s
        11,203,021,806      cycles

    tcp without tso/gso *
      739 MB/s 12548 msg/s 12548 calls/s
        11,205,483,630      cycles

    udp
      876 MB/s 14873 msg/s 624666 calls/s
        11,205,777,429      cycles

    udp gso
     2139 MB/s 36282 msg/s 36282 calls/s
        11,204,374,561      cycles

   [*] after reverting commit 0a6b2a1dc2a2
       ("tcp: switch to GSO being always on")

Measured total system cycles ('-a') for one core while pinning both
the network receive path and benchmark process to that core:

  perf stat -a -C 12 -e cycles \
    ./udpgso_bench_tx -C 12 -4 -D "$DST" -l 4

Note the reduction in calls/s with GSO. Bytes per syscall drops
increases from 1470 to 61818.

Signed-off-by: Willem de Bruijn <[email-masked]>
---
 include/linux/skbuff.h   |  9 ++++++++
 include/linux/udp.h      |  1 +
 include/net/inet_sock.h  |  1 +
 include/net/ip.h         |  1 +
 include/net/ipv6.h       |  1 +
 include/net/udp.h        |  4 ++++
 include/uapi/linux/udp.h |  1 +
 net/core/skbuff.c        |  2 ++
 net/ipv4/af_inet.c       |  2 +-
 net/ipv4/ip_output.c     |  7 ++++--
 net/ipv4/udp.c           | 31 +++++++++++++++++++++++---
 net/ipv4/udp_offload.c   | 47 ++++++++++++++++++++++++++++++++++++++++
 net/ipv6/ip6_offload.c   |  5 +++--
 net/ipv6/ip6_output.c    |  4 +++-
 net/ipv6/udp.c           | 21 +++++++++++++++---
 net/ipv6/udp_offload.c   | 14 ++++++++++++
 16 files changed, 139 insertions(+), 12 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 9065477ed255..6850643508c1 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -573,6 +573,8 @@ enum {
 	SKB_GSO_ESP = 1 << 15,
 
 	SKB_GSO_UDP = 1 << 16,
+
+	SKB_GSO_UDP_L4 = 1 << 17,
 };
 
 #if BITS_PER_LONG > 32
@@ -4047,6 +4049,13 @@ static inline bool skb_is_gso_sctp(const struct sk_buff *skb)
 	return skb_shinfo(skb)->gso_type & SKB_GSO_SCTP;
 }
 
+static inline bool skb_is_ufo(const struct sk_buff *skb)
+{
+	const unsigned int gso_type = skb_shinfo(skb)->gso_type;
+
+	return (gso_type & (SKB_GSO_UDP | SKB_GSO_UDP_L4)) == SKB_GSO_UDP;
+}
+
 static inline void skb_gso_reset(struct sk_buff *skb)
 {
 	skb_shinfo(skb)->gso_size = 0;
diff --git a/include/linux/udp.h b/include/linux/udp.h
index eaea63bc79bb..f7184052ed32 100644
--- a/include/linux/udp.h
+++ b/include/linux/udp.h
@@ -55,6 +55,7 @@ struct udp_sock {
 	 * when the socket is uncorked.
 	 */
 	__u16		 len;		/* total length of pending frames */
+	__u16		 gso_size;
 	/*
 	 * Fields specific to UDP-Lite.
 	 */
diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
index 0a671c32d6b9..83d5b3c2ac42 100644
--- a/include/net/inet_sock.h
+++ b/include/net/inet_sock.h
@@ -147,6 +147,7 @@ struct inet_cork {
 	__u8			ttl;
 	__s16			tos;
 	char			priority;
+	__u16			gso_size;
 };
 
 struct inet_cork_full {
diff --git a/include/net/ip.h b/include/net/ip.h
index 5a0d2b660506..1190d10fb9b2 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -76,6 +76,7 @@ struct ipcm_cookie {
 	__u8			ttl;
 	__s16			tos;
 	char			priority;
+	__u16			gso_size;
 };
 
 #define IPCB(skb) ((struct inet_skb_parm*)((skb)->cb))
diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index 0dd722cab037..0a872a7c33c8 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -298,6 +298,7 @@ struct ipcm6_cookie {
 	__s16 tclass;
 	__s8  dontfrag;
 	struct ipv6_txoptions *opt;
+	__u16 gso_size;
 };
 
 static inline struct ipv6_txoptions *txopt_get(const struct ipv6_pinfo *np)
diff --git a/include/net/udp.h b/include/net/udp.h
index 0676b272f6ac..741d888d0fdb 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -174,6 +174,10 @@ struct sk_buff **udp_gro_receive(struct sk_buff **head, struct sk_buff *skb,
 				 struct udphdr *uh, udp_lookup_t lookup);
 int udp_gro_complete(struct sk_buff *skb, int nhoff, udp_lookup_t lookup);
 
+struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
+				  netdev_features_t features,
+				  unsigned int mss, __sum16 check);
+
 static inline struct udphdr *udp_gro_udphdr(struct sk_buff *skb)
 {
 	struct udphdr *uh;
diff --git a/include/uapi/linux/udp.h b/include/uapi/linux/udp.h
index efb7b5991c2f..09d00f8c442b 100644
--- a/include/uapi/linux/udp.h
+++ b/include/uapi/linux/udp.h
@@ -32,6 +32,7 @@ struct udphdr {
 #define UDP_ENCAP	100	/* Set the socket to accept encapsulated packets */
 #define UDP_NO_CHECK6_TX 101	/* Disable sending checksum for UDP6X */
 #define UDP_NO_CHECK6_RX 102	/* Disable accpeting checksum for UDP6 */
+#define UDP_SEGMENT	103	/* Set GSO segmentation size */
 
 /* UDP encapsulation types */
 #define UDP_ENCAP_ESPINUDP_NON_IKE	1 /* draft-ietf-ipsec-nat-t-ike-00/01 */
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 345b51837ca8..3eed21f64e0b 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -4926,6 +4926,8 @@ static unsigned int skb_gso_transport_seglen(const struct sk_buff *skb)
 		thlen = tcp_hdrlen(skb);
 	} else if (unlikely(skb_is_gso_sctp(skb))) {
 		thlen = sizeof(struct sctphdr);
+	} else if (shinfo->gso_type & SKB_GSO_UDP_L4) {
+		thlen = sizeof(struct udphdr);
 	}
 	/* UFO sets gso_size to the size of the fragmentation
 	 * payload, i.e. the size of the L4 (UDP) header is already
diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 3ebf599cebae..d6c3cd02ca2a 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1327,7 +1327,7 @@ struct sk_buff *inet_gso_segment(struct sk_buff *skb,
 	segs = ERR_PTR(-EPROTONOSUPPORT);
 
 	if (!skb->encapsulation || encap) {
-		udpfrag = !!(skb_shinfo(skb)->gso_type & SKB_GSO_UDP);
+		udpfrag = skb_is_ufo(skb);
 		fixedid = !!(skb_shinfo(skb)->gso_type & SKB_GSO_TCP_FIXEDID);
 
 		/* fixed ID is invalid if DF bit is not set */
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 83b14ea16654..7abfb24ec5e5 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -882,7 +882,8 @@ static int __ip_append_data(struct sock *sk,
 	skb = skb_peek_tail(queue);
 
 	exthdrlen = !skb ? rt->dst.header_len : 0;
-	mtu = cork->fragsize;
+	mtu = cork->gso_size ? IP_MAX_MTU : cork->fragsize;
+
 	if (cork->tx_flags & SKBTX_ANY_SW_TSTAMP &&
 	    sk->sk_tsflags & SOF_TIMESTAMPING_OPT_ID)
 		tskey = sk->sk_tskey++;
@@ -1133,6 +1134,8 @@ static int ip_setup_cork(struct sock *sk, struct inet_cork *cork,
 	*rtp = NULL;
 	cork->fragsize = ip_sk_use_pmtu(sk) ?
 			 dst_mtu(&rt->dst) : rt->dst.dev->mtu;
+
+	cork->gso_size = sk->sk_type == SOCK_DGRAM ? ipc->gso_size : 0;
 	cork->dst = &rt->dst;
 	cork->length = 0;
 	cork->ttl = ipc->ttl;
@@ -1212,7 +1215,7 @@ ssize_t	ip_append_page(struct sock *sk, struct flowi4 *fl4, struct page *page,
 		return -EOPNOTSUPP;
 
 	hh_len = LL_RESERVED_SPACE(rt->dst.dev);
-	mtu = cork->fragsize;
+	mtu = cork->gso_size ? IP_MAX_MTU : cork->fragsize;
 
 	fragheaderlen = sizeof(struct iphdr) + (opt ? opt->optlen : 0);
 	maxfraglen = ((mtu - fragheaderlen) & ~7) + fragheaderlen;
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 6b9d8017b319..731772a69043 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -757,7 +757,8 @@ void udp_set_csum(bool nocheck, struct sk_buff *skb,
 }
 EXPORT_SYMBOL(udp_set_csum);
 
-static int udp_send_skb(struct sk_buff *skb, struct flowi4 *fl4)
+static int udp_send_skb(struct sk_buff *skb, struct flowi4 *fl4,
+			struct inet_cork *cork)
 {
 	struct sock *sk = skb->sk;
 	struct inet_sock *inet = inet_sk(sk);
@@ -777,6 +778,19 @@ static int udp_send_skb(struct sk_buff *skb, struct flowi4 *fl4)
 	uh->len = htons(len);
 	uh->check = 0;
 
+	if (cork->gso_size) {
+		const int hlen = skb_network_header_len(skb) +
+				 sizeof(struct udphdr);
+
+		if (hlen + cork->gso_size > cork->fragsize)
+			return -EINVAL;
+		if (skb->ip_summed != CHECKSUM_PARTIAL || is_udplite)
+			return -EIO;
+
+		skb_shinfo(skb)->gso_size = cork->gso_size;
+		skb_shinfo(skb)->gso_type = SKB_GSO_UDP | SKB_GSO_UDP_L4;
+	}
+
 	if (is_udplite)  				 /*     UDP-Lite      */
 		csum = udplite_csum(skb);
 
@@ -828,7 +842,7 @@ int udp_push_pending_frames(struct sock *sk)
 	if (!skb)
 		goto out;
 
-	err = udp_send_skb(skb, fl4);
+	err = udp_send_skb(skb, fl4, &inet->cork.base);
 
 out:
 	up->len = 0;
@@ -922,6 +936,7 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	ipc.sockc.tsflags = sk->sk_tsflags;
 	ipc.addr = inet->inet_saddr;
 	ipc.oif = sk->sk_bound_dev_if;
+	ipc.gso_size = up->gso_size;
 
 	if (msg->msg_controllen) {
 		err = ip_cmsg_send(sk, msg, &ipc, sk->sk_family == AF_INET6);
@@ -1037,7 +1052,7 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 				  &cork, msg->msg_flags);
 		err = PTR_ERR(skb);
 		if (!IS_ERR_OR_NULL(skb))
-			err = udp_send_skb(skb, fl4);
+			err = udp_send_skb(skb, fl4, &cork);
 		goto out;
 	}
 
@@ -2367,6 +2382,12 @@ int udp_lib_setsockopt(struct sock *sk, int level, int optname,
 		up->no_check6_rx = valbool;
 		break;
 
+	case UDP_SEGMENT:
+		if (val < 0 || val > USHRT_MAX)
+			return -EINVAL;
+		up->gso_size = val;
+		break;
+
 	/*
 	 * 	UDP-Lite's partial checksum coverage (RFC 3828).
 	 */
@@ -2457,6 +2478,10 @@ int udp_lib_getsockopt(struct sock *sk, int level, int optname,
 		val = up->no_check6_rx;
 		break;
 
+	case UDP_SEGMENT:
+		val = up->gso_size;
+		break;
+
 	/* The following two cannot be changed on UDP sockets, the return is
 	 * always 0 (which corresponds to the full checksum coverage of UDP). */
 	case UDPLITE_SEND_CSCOV:
diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index ea6e6e7df0ee..3378f8dec9c7 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -187,6 +187,50 @@ struct sk_buff *skb_udp_tunnel_segment(struct sk_buff *skb,
 }
 EXPORT_SYMBOL(skb_udp_tunnel_segment);
 
+struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
+				  netdev_features_t features,
+				  unsigned int mss, __sum16 check)
+{
+	struct udphdr *uh = udp_hdr(gso_skb);
+	struct sk_buff *segs;
+	unsigned int hdrlen;
+
+	if (gso_skb->len <= sizeof(*uh) + mss)
+		return ERR_PTR(-EINVAL);
+
+	uh->len = htons(sizeof(*uh) + mss);
+	uh->check = check;
+	skb_pull(gso_skb, sizeof(*uh));
+	hdrlen = gso_skb->data - skb_mac_header(gso_skb);
+
+	segs = skb_segment(gso_skb, features);
+	if (unlikely(IS_ERR_OR_NULL(segs)))
+		return segs;
+
+	/* If last packet is not full, fix up its header */
+	if (segs->prev->len != hdrlen + mss) {
+		unsigned int mss_last = segs->prev->len - hdrlen;
+
+		uh = udp_hdr(segs->prev);
+		uh->len = htons(sizeof(*uh) + mss_last);
+		csum_replace2(&uh->check, htons(mss), htons(mss_last));
+	}
+
+	return segs;
+}
+
+static struct sk_buff *__udp4_gso_segment(struct sk_buff *gso_skb,
+					  netdev_features_t features)
+{
+	const struct iphdr *iph = ip_hdr(gso_skb);
+	unsigned int mss = skb_shinfo(gso_skb)->gso_size;
+
+	return __udp_gso_segment(gso_skb, features, mss,
+				 udp_v4_check(sizeof(struct udphdr) + mss,
+					      iph->saddr, iph->daddr, 0));
+}
+EXPORT_SYMBOL_GPL(__udp4_gso_segment);
+
 static struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
 					 netdev_features_t features)
 {
@@ -209,6 +253,9 @@ static struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
 	if (!pskb_may_pull(skb, sizeof(struct udphdr)))
 		goto out;
 
+	if (!skb_is_ufo(skb))
+		return __udp4_gso_segment(skb, features);
+
 	mss = skb_shinfo(skb)->gso_size;
 	if (unlikely(skb->len <= mss))
 		goto out;
diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c
index 4a87f9428ca5..e59f67c0bf89 100644
--- a/net/ipv6/ip6_offload.c
+++ b/net/ipv6/ip6_offload.c
@@ -88,9 +88,10 @@ static struct sk_buff *ipv6_gso_segment(struct sk_buff *skb,
 
 	if (skb->encapsulation &&
 	    skb_shinfo(skb)->gso_type & (SKB_GSO_IPXIP4 | SKB_GSO_IPXIP6))
-		udpfrag = proto == IPPROTO_UDP && encap;
+		udpfrag = proto == IPPROTO_UDP && encap && skb_is_ufo(skb);
 	else
-		udpfrag = proto == IPPROTO_UDP && !skb->encapsulation;
+		udpfrag = proto == IPPROTO_UDP && !skb->encapsulation &&
+			  skb_is_ufo(skb);
 
 	ops = rcu_dereference(inet6_offloads[proto]);
 	if (likely(ops && ops->callbacks.gso_segment)) {
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 6751f4c375b9..3ce947c1d173 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1234,6 +1234,8 @@ static int ip6_setup_cork(struct sock *sk, struct inet_cork_full *cork,
 	if (mtu < IPV6_MIN_MTU)
 		return -EINVAL;
 	cork->base.fragsize = mtu;
+	cork->base.gso_size = sk->sk_type == SOCK_DGRAM ? ipc6->gso_size : 0;
+
 	if (dst_allfrag(xfrm_dst_path(&rt->dst)))
 		cork->base.flags |= IPCORK_ALLFRAG;
 	cork->base.length = 0;
@@ -1275,7 +1277,7 @@ static int __ip6_append_data(struct sock *sk,
 		dst_exthdrlen = rt->dst.header_len - rt->rt6i_nfheader_len;
 	}
 
-	mtu = cork->fragsize;
+	mtu = cork->gso_size ? IP6_MAX_MTU : cork->fragsize;
 	orig_mtu = mtu;
 
 	hh_len = LL_RESERVED_SPACE(rt->dst.dev);
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 824797f8d1ab..16aee23b1e5f 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -1023,7 +1023,8 @@ static void udp6_hwcsum_outgoing(struct sock *sk, struct sk_buff *skb,
  *	Sending
  */
 
-static int udp_v6_send_skb(struct sk_buff *skb, struct flowi6 *fl6)
+static int udp_v6_send_skb(struct sk_buff *skb, struct flowi6 *fl6,
+			   struct inet_cork *cork)
 {
 	struct sock *sk = skb->sk;
 	struct udphdr *uh;
@@ -1042,6 +1043,19 @@ static int udp_v6_send_skb(struct sk_buff *skb, struct flowi6 *fl6)
 	uh->len = htons(len);
 	uh->check = 0;
 
+	if (cork->gso_size) {
+		const int hlen = skb_network_header_len(skb) +
+				 sizeof(struct udphdr);
+
+		if (hlen + cork->gso_size > cork->fragsize)
+			return -EINVAL;
+		if (skb->ip_summed != CHECKSUM_PARTIAL || is_udplite)
+			return -EIO;
+
+		skb_shinfo(skb)->gso_size = cork->gso_size;
+		skb_shinfo(skb)->gso_type = SKB_GSO_UDP | SKB_GSO_UDP_L4;
+	}
+
 	if (is_udplite)
 		csum = udplite_csum(skb);
 	else if (udp_sk(sk)->no_check6_tx) {   /* UDP csum disabled */
@@ -1093,7 +1107,7 @@ static int udp_v6_push_pending_frames(struct sock *sk)
 	if (!skb)
 		goto out;
 
-	err = udp_v6_send_skb(skb, &fl6);
+	err = udp_v6_send_skb(skb, &fl6, &inet_sk(sk)->cork.base);
 
 out:
 	up->len = 0;
@@ -1127,6 +1141,7 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	ipc6.hlimit = -1;
 	ipc6.tclass = -1;
 	ipc6.dontfrag = -1;
+	ipc6.gso_size = up->gso_size;
 	sockc.tsflags = sk->sk_tsflags;
 
 	/* destination address check */
@@ -1333,7 +1348,7 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 				   msg->msg_flags, &cork, &sockc);
 		err = PTR_ERR(skb);
 		if (!IS_ERR_OR_NULL(skb))
-			err = udp_v6_send_skb(skb, &fl6);
+			err = udp_v6_send_skb(skb, &fl6, &cork.base);
 		goto out;
 	}
 
diff --git a/net/ipv6/udp_offload.c b/net/ipv6/udp_offload.c
index 2a04dc9c781b..7410120fc114 100644
--- a/net/ipv6/udp_offload.c
+++ b/net/ipv6/udp_offload.c
@@ -17,6 +17,17 @@
 #include <net/ip6_checksum.h>
 #include "ip6_offload.h"
 
+static struct sk_buff *__udp6_gso_segment(struct sk_buff *gso_skb,
+					  netdev_features_t features)
+{
+	const struct ipv6hdr *ip6h = ipv6_hdr(gso_skb);
+	unsigned int mss = skb_shinfo(gso_skb)->gso_size;
+
+	return __udp_gso_segment(gso_skb, features, mss,
+				 udp_v6_check(sizeof(struct udphdr) + mss,
+					      &ip6h->saddr, &ip6h->daddr, 0));
+}
+
 static struct sk_buff *udp6_ufo_fragment(struct sk_buff *skb,
 					 netdev_features_t features)
 {
@@ -48,6 +59,9 @@ static struct sk_buff *udp6_ufo_fragment(struct sk_buff *skb,
 		if (!pskb_may_pull(skb, sizeof(struct udphdr)))
 			goto out;
 
+		if (!skb_is_ufo(skb))
+			return __udp6_gso_segment(skb, features);
+
 		/* Do software UFO. Complete and fill in the UDP checksum as HW cannot
 		 * do checksum of UDP packets sent as multiple IP fragments.
 		 */
-- 
2.17.0.484.g0c8726318c-goog