Re: [PATCH net-next 2/3] myri10ge: Add vlan rx for better GRO perf.

On 11/14/12 09:46, Eric Dumazet wrote:

On Wed, 2012-11-14 at 08:06 -0500, Andrew Gallatin wrote:

quoted

Unlike LRO, GRO requires that vlan tags be removed before
aggregation can occur.  Since the myri10ge NIC does not support
hardware vlan tag offload, we must remove the tag in the driver
to achieve performance comparable to LRO for vlan tagged frames.

Signed-off-by: Andrew Gallatin <redacted>
---
   drivers/net/ethernet/myricom/myri10ge/myri10ge.c |   47
++++++++++++++++++++++
   1 file changed, 47 insertions(+)

diff --git a/drivers/net/ethernet/myricom/myri10ge/myri10ge.c

b/drivers/net/ethernet/myricom/myri10ge/myri10ge.c
index a5ab2f2..b9b6dfd 100644

--- a/drivers/net/ethernet/myricom/myri10ge/myri10ge.c
+++ b/drivers/net/ethernet/myricom/myri10ge/myri10ge.c

@@ -1264,6 +1264,48 @@ myri10ge_unmap_rx_page(struct pci_dev *pdev,
   	}
   }

+/*
+ * GRO does not support acceleration of tagged vlan frames, and
+ * this NIC does not support vlan tag offload, so we must pop
+ * the tag ourselves to be able to achieve GRO performance that
+ * is comparable to LRO.
+ */
+
+static inline void
+myri10ge_vlan_rx(struct net_device *dev, void *addr, struct sk_buff *skb)
+{
+	u8 *va;
+	struct vlan_ethhdr *veh;
+	struct ethhdr *eh;
+	struct skb_frag_struct *frag;
+	u16 proto;
+
+	va = addr;
+	va += MXGEFW_PAD;
+	veh = (struct vlan_ethhdr *) va;
+	if ((dev->features & (NETIF_F_HW_VLAN_RX | NETIF_F_GRO)) ==
+	    (NETIF_F_HW_VLAN_RX | NETIF_F_GRO) &&
+	    (veh->h_vlan_proto == ntohs(ETH_P_8021Q))) {
+		/* fixup csum if needed */
+		if (skb->ip_summed == CHECKSUM_COMPLETE)
+			skb->csum = csum_sub(skb->csum,
+					     csum_partial(va + ETH_HLEN,
+							  VLAN_HLEN, 0));
+		/* pop tag */
+		__vlan_hwaccel_put_tag(skb, ntohs(veh->h_vlan_TCI));
+		proto = veh->h_vlan_encapsulated_proto;

I am not sure you need this @proto ?

quoted

+		memmove(va + VLAN_HLEN, va, ETH_HLEN);

You could only memmove the mac addresses (2 * ETH_ALEN)
To not touch the proto (and avoid possible aliasing problems)

quoted

+		va += VLAN_HLEN;
+		eh = (struct ethhdr *)va;
+		eh->h_proto = proto;

and this should not be needed ?

Indeed, your suggestion works and is simpler and less risky.
Thank you for your help.

I also think that I am making a mistake by only popping the tag when
GRO is enabled.  My fear is that something will become confused when
skb->dev->features contains NETIF_F_HW_VLAN_RX, but the tag is not
decap'ed.  So I will remove the check for NETIF_F_GRO when popping
the vlan tag.

Thanks,

Drew