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authorEd Cashin <ecashin@coraid.com>2012-09-19 15:49:00 +0000
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-10-13 05:28:08 +0900
commit70875a0484cf2ce1864dab9f453bcc072f4b71c7 (patch)
tree264af58d6efc52716c0d6b764b440384c5fc8b91 /net
parent6a992a944a1c283359959745cb5e1f1dbca40a16 (diff)
net: do not disable sg for packets requiring no checksum
[ Upstream commit c0d680e577ff171e7b37dbdb1b1bf5451e851f04 ] 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 <jesse@nicira.com> 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: http://www.spinics.net/lists/linux-mm/msg15184.html The problem has probably not been widely experienced yet, because only recently has the kernel.org-distributed aoe driver acquired the ability to use payloads of over a page in size, with the patchset recently included in the mm tree: https://lkml.org/lkml/2012/8/28/140 The coraid.com-distributed 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 <ecashin@coraid.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'net')
-rw-r--r--net/core/dev.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/net/core/dev.c b/net/core/dev.c
index df6ee2884e7a..5b84eafb1a63 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2038,7 +2038,8 @@ static bool can_checksum_protocol(unsigned long features, __be16 protocol)
static u32 harmonize_features(struct sk_buff *skb, __be16 protocol, u32 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)) {