Problem:
-------
GRO is enabled on the interfaces in the following test,
but GRO does not take effect for vxlan-encapsulated tcp streams. The
root
cause of why GRO does not take effect is described below.
VM nic (mtu 1450)---bridge---vxlan----10Gb nic (intel 82599ES)-----|
VM nic (mtu 1450)---bridge---vxlan----10Gb nic (intel 82599ES)-----|
Because gro is not effective, the throughput for vxlan-encapsulated
tcp-stream is around 3 Gbps.
With the proposed patch, gro takes effect for vxlan-encapsulated tcp
streams,
and performance in the same test is around 8.6 Gbps.
Root Cause:
----------
At entry to udp4_gro_receive(), the gro parameters are set as follows:
skb->ip_summed == 0 (CHECKSUM_NONE)
NAPI_GRO_CB(skb)->csum_cnt == 0
NAPI_GRO_CB(skb)->csum_valid == 0
UDH header checksum is 0.
static struct sk_buff **udp4_gro_receive(struct sk_buff **head,
struct sk_buff *skb)
{
<snip>
if (skb_gro_checksum_validate_zero_check(skb, IPPROTO_UDP, uh->check,
inet_gro_compute_pseudo))
This calls __skb_incr_checksum_unnecessary which sets
skb->ip_summed to CHECKSUM_UNNECESSARY
goto flush;
else if (uh->check)
skb_gro_checksum_try_convert(skb, IPPROTO_UDP, uh->check,
inet_gro_compute_pseudo);
skip:
NAPI_GRO_CB(skb)->is_ipv6 = 0;
return udp_gro_receive(head, skb, uh);
}
struct sk_buff **udp_gro_receive(struct sk_buff **head, struct sk_buff
*skb,
struct udphdr *uh)
{
struct udp_offload_priv *uo_priv;
struct sk_buff *p, **pp = NULL;
struct udphdr *uh2;
unsigned int off = skb_gro_offset(skb);
int flush = 1;
if (NAPI_GRO_CB(skb)->udp_mark ||
(skb->ip_summed != CHECKSUM_PARTIAL &&
NAPI_GRO_CB(skb)->csum_cnt == 0 &&
!NAPI_GRO_CB(skb)->csum_valid))
goto out;
vxlan GRO gets skipped due to the above condition because here,:
skb->ip_summed == CHECKSUM_UNNECESSARY
NAPI_GRO_CB(skb)->csum_cnt == 0
NAPI_GRO_CB(skb)->csum_valid == 0
There is no reason for skipping vxlan gro in the above combination of
conditions,
because, tcp4_gro_receive() validates the inner tcp checksum anyway !
Patch:
------
Signed-off-by: Ramu Ramamurthy <ramu.ramamur...@us.ibm.com>
---
net/ipv4/udp_offload.c | 1 +
1 files changed, 1 insertions(+), 0 deletions(-)
diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index f938616..17fc12b 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -301,6 +301,7 @@ struct sk_buff **udp_gro_receive(struct sk_buff
**head, struct sk_buff *skb,
if (NAPI_GRO_CB(skb)->udp_mark ||
(skb->ip_summed != CHECKSUM_PARTIAL &&
+ skb->ip_summed != CHECKSUM_UNNECESSARY &&
NAPI_GRO_CB(skb)->csum_cnt == 0 &&
!NAPI_GRO_CB(skb)->csum_valid))
goto out;
--
1.7.1
Notes:
-------
The above gro fix applies to all udp-encapsulation protocols (vxlan,
geneve)
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