diff options
authorEd Cashin <>2012-09-19 15:49:00 +0000
committerDavid S. Miller <>2012-09-20 22:23:40 -0400
commitc0d680e577ff171e7b37dbdb1b1bf5451e851f04 (patch)
parent8babe8cc6570ed896b7b596337eb8fe730c3ff45 (diff)
net: do not disable sg for packets requiring no checksum
A change in a series of VLAN-related changes appears to have inadvertently disabled the use of the scatter gather feature of network cards for transmission of non-IP ethernet protocols like ATA over Ethernet (AoE). Below is a reference to the commit that introduces a "harmonize_features" function that turns off scatter gather when the NIC does not support hardware checksumming for the ethernet protocol of an sk buff. commit f01a5236bd4b140198fbcc550f085e8361fd73fa Author: Jesse Gross <> Date: Sun Jan 9 06:23:31 2011 +0000 net offloading: Generalize netif_get_vlan_features(). The can_checksum_protocol function is not equipped to consider a protocol that does not require checksumming. Calling it for a protocol that requires no checksum is inappropriate. The patch below has harmonize_features call can_checksum_protocol when the protocol needs a checksum, so that the network layer is not forced to perform unnecessary skb linearization on the transmission of AoE packets. Unnecessary linearization results in decreased performance and increased memory pressure, as reported here: The problem has probably not been widely experienced yet, because only recently has the aoe driver acquired the ability to use payloads of over a page in size, with the patchset recently included in the mm tree: The aoe driver already could use payloads of greater than a page in size, but its users generally do not use the newest kernels. Signed-off-by: Ed Cashin <> Signed-off-by: David S. Miller <>
1 files changed, 2 insertions, 1 deletions
diff --git a/net/core/dev.c b/net/core/dev.c
index ac7609d8518..89e33a5d4d9 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2134,7 +2134,8 @@ static bool can_checksum_protocol(netdev_features_t features, __be16 protocol)
static netdev_features_t harmonize_features(struct sk_buff *skb,
__be16 protocol, netdev_features_t features)
- if (!can_checksum_protocol(features, protocol)) {
+ if (skb->ip_summed != CHECKSUM_NONE &&
+ !can_checksum_protocol(features, protocol)) {
features &= ~NETIF_F_ALL_CSUM;
features &= ~NETIF_F_SG;
} else if (illegal_highdma(skb->dev, skb)) {