[PATCH net-next 0/6] net: Checksum offload changes - Part VI

[PATCH net-next 0/6] net: Checksum offload changes - Part VI

[Tom Herbert]

I am working on overhauling RX checksum offload. Goals of this effort
are:

- Specify what exactly it means when driver returns CHECKSUM_UNNECESSARY
- Preserve CHECKSUM_COMPLETE through encapsulation layers
- Don't do skb_checksum more than once per packet
- Unify GRO and non-GRO csum verification as much as possible
- Unify the checksum functions (checksum_init)
- Simplify code

What is in this seventh patch set:

- Add skb->csum. This allows a device or GRO to indicate that an
  invalid checksum was detected.
- Checksum unncessary to checksum complete conversions.

With these changes, I believe that the third goal of the overhaul is
now mostly achieved. In the case of no encapsulation or one layer of
encapsulation, there should only be at most one skb_checksum over
each packet (between GRO and normal path). In the case of two layers
of encapsulation, it is still possible with the right combination of
non-zero and zero UDP checksums to have >1 skb_checksum. For instance:
IP>GRE(with csum)>IP>UDP(zero csum)>VXLAN>IP>UDP(non-zero csum),
would likely necessiate an skb_checksum in GRO and normal path.
This doesn't seem like a common scenario at all so I'm inclined to
not address this now, if multiple layers of encapsulation becomes
popular we can reassess.

Note that checksum conversion shows a nice improvement for RX VXLAN when
outer UDP checksum is enabled (12.65% CPU compared to 20.94%). This
is not only from the fact that we don't need checksum calculation on
the host, but also allows GRO for VXLAN in this case. Checksum
conversion does not help send side (which still needs to perform
a checksum on host). For that we will implement remote checksum offload
in a later patch
(http://tools.ietf.org/html/draft-herbert-remotecsumoffload-00).

Please review carefully and test if possible, mucking with basic
checksum functions is always a little precarious :-)

----

Test results with this patch set are below. I did not see any
obvious performace regression.

Tests run:
   TCP_STREAM: super_netperf with 200 streams

Device bnx2x (10Gbps):
   VXLAN UDP RSS port hashing enabled, UDP RX checksum offload supported.

* VXLAN with checksum
  With fix:
    TCP_STREAM
        12.65% CPU utilization
        9093.81 Mbps
  Without fix:
    TCP_STREAM
        20.94% CPU utilization
        9094.21 Mbps

* VXLAN without checksum
  With fix:
    TCP_STREAM
        24.59% CPU utilization
        9080.96 Mbps
  Without fix:
    TCP_STREAM
        24.69% CPU utilization
        9081.39 Mbps

Tom Herbert (6):
  net: Support for csum_bad in skbuff
  net: Infrastructure for checksum unnecessary conversions
  udp: Add support for doing checksum unnecessary conversion
  gre: Add support for checksum unnecessary conversions
  vxlan: Enable checksum unnecessary conversions for vxlan/UDP sockets
  l2tp: Enable checksum unnecessary conversions for l2tp/UDP sockets

 drivers/net/vxlan.c       |  2 ++
 include/linux/netdevice.h | 24 +++++++++++++++++++++++-
 include/linux/skbuff.h    | 41 ++++++++++++++++++++++++++++++++++++++++-
 include/linux/udp.h       | 16 +++++++++++++++-
 net/core/dev.c            |  2 +-
 net/ipv4/gre_demux.c      |  4 ++++
 net/ipv4/gre_offload.c    |  8 ++++++--
 net/ipv4/udp.c            |  4 ++++
 net/ipv4/udp_offload.c    | 25 +++++++++++++++++--------
 net/ipv6/udp.c            |  4 ++++
 net/ipv6/udp_offload.c    | 24 +++++++++++++++++-------
 net/l2tp/l2tp_core.c      |  2 ++
 12 files changed, 135 insertions(+), 21 deletions(-)

-- 
2.1.0.rc2.206.gedb03e5

[PATCH net-next 1/6] net: Support for csum_bad in skbuff

[Tom Herbert]

This flag indicates that an invalid checksum was detected in the
packet. __skb_mark_checksum_bad helper function was added to set this.

Checksums can be marked bad from a driver or the GRO path (the latter
is implemented in this patch). csum_bad is checked in
__skb_checksum_validate_complete (i.e. calling that when ip_summed ==
CHECKSUM_NONE).

csum_bad works in conjunction with ip_summed value. In the case that
ip_summed is CHECKSUM_NONE and csum_bad is set, this implies that the
first (or next) checksum encountered in the packet is bad. When
ip_summed is CHECKSUM_UNNECESSARY, the first checksum after the last
one validated is bad. For example, if ip_summed == CHECKSUM_UNNECESSARY,
csum_level == 1, and csum_bad is set-- then the third checksum in the
packet is bad. In the normal path, the packet will be dropped when
processing the protocol layer of the bad checksum:
__skb_decr_checksum_unnecessary called twice for the good checksums
changing ip_summed to CHECKSUM_NONE so that
__skb_checksum_validate_complete is called to validate the third
checksum and that will fail since csum_bad is set.

Signed-off-by: Tom Herbert <therbert@google.com>
---
 include/linux/netdevice.h |  4 +++-
 include/linux/skbuff.h    | 21 ++++++++++++++++++++-
 net/core/dev.c            |  2 +-
 3 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 456eb1f..024d8c1 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2216,7 +2216,9 @@ static inline void skb_gro_incr_csum_unnecessary(struct sk_buff *skb)
 	if (__skb_gro_checksum_validate_needed(skb, zero_okay, check))	\
 		__ret = __skb_gro_checksum_validate_complete(skb,	\
 				compute_pseudo(skb, proto));		\
-	if (!__ret)							\
+	if (__ret)							\
+		__skb_mark_checksum_bad(skb);				\
+	else								\
 		skb_gro_incr_csum_unnecessary(skb);			\
 	__ret;								\
 })
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index c93b585..23710a2 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -617,7 +617,8 @@ struct sk_buff {
 
 	kmemcheck_bitfield_begin(flags3);
 	__u8			csum_level:2;
-	/* 14 bit hole */
+	__u8			csum_bad:1;
+	/* 13 bit hole */
 	kmemcheck_bitfield_end(flags3);
 
 	__be16			inner_protocol;
@@ -2825,6 +2826,21 @@ static inline void __skb_incr_checksum_unnecessary(struct sk_buff *skb)
 	}
 }
 
+static inline void __skb_mark_checksum_bad(struct sk_buff *skb)
+{
+	/* Mark current checksum as bad (typically called from GRO
+	 * path). In the case that ip_summed is CHECKSUM_NONE
+	 * this must be the first checksum encountered in the packet.
+	 * When ip_summed is CHECKSUM_UNNECESSARY, this is the first
+	 * checksum after the last one validated. For UDP, a zero
+	 * checksum can not be marked as bad.
+	 */
+
+	if (skb->ip_summed == CHECKSUM_NONE ||
+	    skb->ip_summed == CHECKSUM_UNNECESSARY)
+		skb->csum_bad = 1;
+}
+
 /* Check if we need to perform checksum complete validation.
  *
  * Returns true if checksum complete is needed, false otherwise
@@ -2866,6 +2882,9 @@ static inline __sum16 __skb_checksum_validate_complete(struct sk_buff *skb,
 			skb->csum_valid = 1;
 			return 0;
 		}
+	} else if (skb->csum_bad) {
+		/* ip_summed == CHECKSUM_NONE in this case */
+		return 1;
 	}
 
 	skb->csum = psum;
diff --git a/net/core/dev.c b/net/core/dev.c
index a6077ef..960df22 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3957,7 +3957,7 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 	if (!(skb->dev->features & NETIF_F_GRO))
 		goto normal;
 
-	if (skb_is_gso(skb) || skb_has_frag_list(skb))
+	if (skb_is_gso(skb) || skb_has_frag_list(skb) || skb->csum_bad)
 		goto normal;
 
 	gro_list_prepare(napi, skb);
-- 
2.1.0.rc2.206.gedb03e5

[PATCH net-next 2/6] net: Infrastructure for checksum unnecessary conversions

[Tom Herbert]

For normal path, added skb_checksum_try_convert which is called
to attempt to convert CHECKSUM_UNNECESSARY to CHECKSUM_COMPLETE. The
primary condition to allow this is that ip_summed is CHECKSUM_NONE
and csum_valid is true, which will be the state after consuming
a CHECKSUM_UNNECESSARY.

For GRO path, added skb_gro_checksum_try_convert which is the GRO
analogue of skb_checksum_try_convert. The primary condition to allow
this is that NAPI_GRO_CB(skb)->csum_cnt == 0 and
NAPI_GRO_CB(skb)->csum_valid is set. This implies that we have consumed
all available CHECKSUM_UNNECESSARY checksums in the GRO path.

Signed-off-by: Tom Herbert <therbert@google.com>
---
 include/linux/netdevice.h | 20 ++++++++++++++++++++
 include/linux/skbuff.h    | 20 ++++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 024d8c1..9d4ab3e 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2233,6 +2233,26 @@ static inline void skb_gro_incr_csum_unnecessary(struct sk_buff *skb)
 #define skb_gro_checksum_simple_validate(skb)				\
 	__skb_gro_checksum_validate(skb, 0, false, 0, null_compute_pseudo)
 
+static inline bool __skb_gro_checksum_convert_check(struct sk_buff *skb)
+{
+	return (NAPI_GRO_CB(skb)->csum_cnt == 0 &&
+		!NAPI_GRO_CB(skb)->csum_valid);
+}
+
+static inline void __skb_gro_checksum_convert(struct sk_buff *skb,
+					      __sum16 check, __wsum pseudo)
+{
+	NAPI_GRO_CB(skb)->csum = ~pseudo;
+	NAPI_GRO_CB(skb)->csum_valid = 1;
+}
+
+#define skb_gro_checksum_try_convert(skb, proto, check, compute_pseudo)	\
+do {									\
+	if (__skb_gro_checksum_convert_check(skb))			\
+		__skb_gro_checksum_convert(skb, check,			\
+					   compute_pseudo(skb, proto));	\
+} while (0)
+
 static inline int dev_hard_header(struct sk_buff *skb, struct net_device *dev,
 				  unsigned short type,
 				  const void *daddr, const void *saddr,
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 23710a2..02529fc 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2942,6 +2942,26 @@ static inline __wsum null_compute_pseudo(struct sk_buff *skb, int proto)
 #define skb_checksum_simple_validate(skb)				\
 	__skb_checksum_validate(skb, 0, true, false, 0, null_compute_pseudo)
 
+static inline bool __skb_checksum_convert_check(struct sk_buff *skb)
+{
+	return (skb->ip_summed == CHECKSUM_NONE &&
+		skb->csum_valid && !skb->csum_bad);
+}
+
+static inline void __skb_checksum_convert(struct sk_buff *skb,
+					  __sum16 check, __wsum pseudo)
+{
+	skb->csum = ~pseudo;
+	skb->ip_summed = CHECKSUM_COMPLETE;
+}
+
+#define skb_checksum_try_convert(skb, proto, check, compute_pseudo)	\
+do {									\
+	if (__skb_checksum_convert_check(skb))				\
+		__skb_checksum_convert(skb, check,			\
+				       compute_pseudo(skb, proto));	\
+} while (0)
+
 #if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
 void nf_conntrack_destroy(struct nf_conntrack *nfct);
 static inline void nf_conntrack_put(struct nf_conntrack *nfct)
-- 
2.1.0.rc2.206.gedb03e5

[PATCH net-next 3/6] udp: Add support for doing checksum unnecessary conversion

[Tom Herbert]

Add support for doing CHECKSUM_UNNECESSARY to CHECKSUM_COMPLETE
conversion in UDP tunneling path.

In the normal UDP path, we call skb_checksum_try_convert after locating
the UDP socket. The check is that checksum conversion is enabled for
the socket (new flag in UDP socket) and that checksum field is
non-zero.

In the UDP GRO path, we call skb_gro_checksum_try_convert after
checksum is validated and checksum field is non-zero. Since this is
already in GRO we assume that checksum conversion is always wanted.

Signed-off-by: Tom Herbert <therbert@google.com>
---
 include/linux/udp.h    | 16 +++++++++++++++-
 net/ipv4/udp.c         |  4 ++++
 net/ipv4/udp_offload.c | 25 +++++++++++++++++--------
 net/ipv6/udp.c         |  4 ++++
 net/ipv6/udp_offload.c | 24 +++++++++++++++++-------
 5 files changed, 57 insertions(+), 16 deletions(-)

diff --git a/include/linux/udp.h b/include/linux/udp.h
index 247cfdc..ee32775 100644
--- a/include/linux/udp.h
+++ b/include/linux/udp.h
@@ -49,7 +49,11 @@ struct udp_sock {
 	unsigned int	 corkflag;	/* Cork is required */
 	__u8		 encap_type;	/* Is this an Encapsulation socket? */
 	unsigned char	 no_check6_tx:1,/* Send zero UDP6 checksums on TX? */
-			 no_check6_rx:1;/* Allow zero UDP6 checksums on RX? */
+			 no_check6_rx:1,/* Allow zero UDP6 checksums on RX? */
+			 convert_csum:1;/* On receive, convert checksum
+					 * unnecessary to checksum complete
+					 * if possible.
+					 */
 	/*
 	 * Following member retains the information to create a UDP header
 	 * when the socket is uncorked.
@@ -98,6 +102,16 @@ static inline bool udp_get_no_check6_rx(struct sock *sk)
 	return udp_sk(sk)->no_check6_rx;
 }
 
+static inline void udp_set_convert_csum(struct sock *sk, bool val)
+{
+	udp_sk(sk)->convert_csum = val;
+}
+
+static inline bool udp_get_convert_csum(struct sock *sk)
+{
+	return udp_sk(sk)->convert_csum;
+}
+
 #define udp_portaddr_for_each_entry(__sk, node, list) \
 	hlist_nulls_for_each_entry(__sk, node, list, __sk_common.skc_portaddr_node)
 
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 3549c21..0da3849 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1788,6 +1788,10 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 	if (sk != NULL) {
 		int ret;
 
+		if (udp_sk(sk)->convert_csum && uh->check && !IS_UDPLITE(sk))
+			skb_checksum_try_convert(skb, IPPROTO_UDP, uh->check,
+						 inet_compute_pseudo);
+
 		ret = udp_queue_rcv_skb(sk, skb);
 		sock_put(sk);
 
diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index a6adff9..84e0e05 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -290,16 +290,25 @@ static struct sk_buff **udp4_gro_receive(struct sk_buff **head,
 {
 	struct udphdr *uh = udp_gro_udphdr(skb);
 
-	/* Don't bother verifying checksum if we're going to flush anyway. */
-	if (unlikely(!uh) ||
-	    (!NAPI_GRO_CB(skb)->flush &&
-	     skb_gro_checksum_validate_zero_check(skb, IPPROTO_UDP, uh->check,
-						  inet_gro_compute_pseudo))) {
-		NAPI_GRO_CB(skb)->flush = 1;
-		return NULL;
-	}
+	if (unlikely(!uh))
+		goto flush;
 
+	/* Don't bother verifying checksum if we're going to flush anyway. */
+	if (!NAPI_GRO_CB(skb)->flush)
+		goto skip;
+
+	if (skb_gro_checksum_validate_zero_check(skb, IPPROTO_UDP, uh->check,
+						 inet_gro_compute_pseudo))
+		goto flush;
+	else if (uh->check)
+		skb_gro_checksum_try_convert(skb, IPPROTO_UDP, uh->check,
+					     inet_gro_compute_pseudo);
+skip:
 	return udp_gro_receive(head, skb, uh);
+
+flush:
+	NAPI_GRO_CB(skb)->flush = 1;
+	return NULL;
 }
 
 int udp_gro_complete(struct sk_buff *skb, int nhoff)
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 12fcce8f..f6ba535 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -891,6 +891,10 @@ int __udp6_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 			goto csum_error;
 		}
 
+		if (udp_sk(sk)->convert_csum && uh->check && !IS_UDPLITE(sk))
+			skb_checksum_try_convert(skb, IPPROTO_UDP, uh->check,
+						 ip6_compute_pseudo);
+
 		ret = udpv6_queue_rcv_skb(sk, skb);
 		sock_put(sk);
 
diff --git a/net/ipv6/udp_offload.c b/net/ipv6/udp_offload.c
index b13e377..89cb9a9 100644
--- a/net/ipv6/udp_offload.c
+++ b/net/ipv6/udp_offload.c
@@ -134,16 +134,26 @@ static struct sk_buff **udp6_gro_receive(struct sk_buff **head,
 {
 	struct udphdr *uh = udp_gro_udphdr(skb);
 
+	if (unlikely(!uh))
+		goto flush;
+
 	/* Don't bother verifying checksum if we're going to flush anyway. */
-	if (unlikely(!uh) ||
-	    (!NAPI_GRO_CB(skb)->flush &&
-	     skb_gro_checksum_validate_zero_check(skb, IPPROTO_UDP, uh->check,
-						  ip6_gro_compute_pseudo))) {
-		NAPI_GRO_CB(skb)->flush = 1;
-		return NULL;
-	}
+	if (!NAPI_GRO_CB(skb)->flush)
+		goto skip;
 
+	if (skb_gro_checksum_validate_zero_check(skb, IPPROTO_UDP, uh->check,
+						 ip6_gro_compute_pseudo))
+		goto flush;
+	else if (uh->check)
+		skb_gro_checksum_try_convert(skb, IPPROTO_UDP, uh->check,
+					     ip6_gro_compute_pseudo);
+
+skip:
 	return udp_gro_receive(head, skb, uh);
+
+flush:
+	NAPI_GRO_CB(skb)->flush = 1;
+	return NULL;
 }
 
 int udp6_gro_complete(struct sk_buff *skb, int nhoff)
-- 
2.1.0.rc2.206.gedb03e5

[PATCH net-next 4/6] gre: Add support for checksum unnecessary conversions

[Tom Herbert]

Call skb_checksum_try_convert and skb_gro_checksum_try_convert
after checksum is found present and validated in the GRE header
for normal and GRO paths respectively.

In GRO path, call skb_gro_checksum_try_convert

Signed-off-by: Tom Herbert <therbert@google.com>
---
 net/ipv4/gre_demux.c   | 4 ++++
 net/ipv4/gre_offload.c | 8 ++++++--
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/gre_demux.c b/net/ipv4/gre_demux.c
index 0485bf7..7e0756d 100644
--- a/net/ipv4/gre_demux.c
+++ b/net/ipv4/gre_demux.c
@@ -125,6 +125,10 @@ static int parse_gre_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
 			*csum_err = true;
 			return -EINVAL;
 		}
+
+		skb_checksum_try_convert(skb, IPPROTO_GRE, 0,
+					 null_compute_pseudo);
+
 		options++;
 	}
 
diff --git a/net/ipv4/gre_offload.c b/net/ipv4/gre_offload.c
index a4d7965..d3fe2ac 100644
--- a/net/ipv4/gre_offload.c
+++ b/net/ipv4/gre_offload.c
@@ -172,10 +172,14 @@ static struct sk_buff **gre_gro_receive(struct sk_buff **head,
 	}
 
 	/* Don't bother verifying checksum if we're going to flush anyway. */
-	if ((greh->flags & GRE_CSUM) && !NAPI_GRO_CB(skb)->flush &&
-	    skb_gro_checksum_simple_validate(skb))
+	if ((greh->flags & GRE_CSUM) && !NAPI_GRO_CB(skb)->flush) {
+		if (skb_gro_checksum_simple_validate(skb))
 			goto out_unlock;
 
+		skb_gro_checksum_try_convert(skb, IPPROTO_GRE, 0,
+					     null_compute_pseudo);
+	}
+
 	flush = 0;
 
 	for (p = *head; p; p = p->next) {
-- 
2.1.0.rc2.206.gedb03e5

[PATCH net-next 5/6] vxlan: Enable checksum unnecessary conversions for vxlan/UDP sockets

[Tom Herbert]

Signed-off-by: Tom Herbert <therbert@google.com>
---
 drivers/net/vxlan.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
index 67527f3..53c3ec1 100644
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -2370,6 +2370,8 @@ static struct socket *vxlan_create_sock(struct net *net, bool ipv6,
 	/* Disable multicast loopback */
 	inet_sk(sock->sk)->mc_loop = 0;
 
+	udp_set_convert_csum(sock->sk, true);
+
 	return sock;
 }
 
-- 
2.1.0.rc2.206.gedb03e5

[PATCH net-next 6/6] l2tp: Enable checksum unnecessary conversions for l2tp/UDP sockets

[Tom Herbert]

Signed-off-by: Tom Herbert <therbert@google.com>
---
 net/l2tp/l2tp_core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 1109d3b..797c0af 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1392,6 +1392,8 @@ static int l2tp_tunnel_sock_create(struct net *net,
 		if (err < 0)
 			goto out;
 
+		udp_set_convert_csum(sock->sk, true);
+
 		break;
 
 	case L2TP_ENCAPTYPE_IP:
-- 
2.1.0.rc2.206.gedb03e5

Re: [PATCH net-next 0/6] net: Checksum offload changes - Part VI

[David Miller]

From: Tom Herbert <therbert@google.com>
Date: Sun, 31 Aug 2014 15:12:40 -0700

> I am working on overhauling RX checksum offload. Goals of this effort
> are:
> 
> - Specify what exactly it means when driver returns CHECKSUM_UNNECESSARY
> - Preserve CHECKSUM_COMPLETE through encapsulation layers
> - Don't do skb_checksum more than once per packet
> - Unify GRO and non-GRO csum verification as much as possible
> - Unify the checksum functions (checksum_init)
> - Simplify code
> 
> What is in this seventh patch set:
> 
> - Add skb->csum. This allows a device or GRO to indicate that an
>   invalid checksum was detected.
> - Checksum unncessary to checksum complete conversions.
> 
> With these changes, I believe that the third goal of the overhaul is
> now mostly achieved. In the case of no encapsulation or one layer of
> encapsulation, there should only be at most one skb_checksum over
> each packet (between GRO and normal path). In the case of two layers
> of encapsulation, it is still possible with the right combination of
> non-zero and zero UDP checksums to have >1 skb_checksum. For instance:
> IP>GRE(with csum)>IP>UDP(zero csum)>VXLAN>IP>UDP(non-zero csum),
> would likely necessiate an skb_checksum in GRO and normal path.
> This doesn't seem like a common scenario at all so I'm inclined to
> not address this now, if multiple layers of encapsulation becomes
> popular we can reassess.
> 
> Note that checksum conversion shows a nice improvement for RX VXLAN when
> outer UDP checksum is enabled (12.65% CPU compared to 20.94%). This
> is not only from the fact that we don't need checksum calculation on
> the host, but also allows GRO for VXLAN in this case. Checksum
> conversion does not help send side (which still needs to perform
> a checksum on host). For that we will implement remote checksum offload
> in a later patch
> (http://tools.ietf.org/html/draft-herbert-remotecsumoffload-00).
> 
> Please review carefully and test if possible, mucking with basic
> checksum functions is always a little precarious :-)

Awesome work, I love watching infrastructure gradually fall into
place like this :-)

Series applied, thanks!