Hi,
I use a Xen domU with vanilla Linux 3.19 kernel as a middle node. SG is
switched off via ethtool. I get random packet drops for about 7% of
small packets (pings, TCP ACKs/SYNs/little payload).
From the code in Linux 4.0 it seems that the behavior should be the same.
I posted on Xen-users before with more information:
http://lists.xen.org/archives/html/xen-users/2015-05/msg00170.html
I narrowed down the issue, and the below patch seems to work. Any
comments are highly welcome.
Thanks,
Lennart
diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index d8c1076..f5e403b 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -611,11 +611,19 @@ static int xennet_start_xmit(struct sk_buff *skb,
struct net_device *dev)
spin_lock_irqsave(&queue->tx_lock, flags);
if (unlikely(!netif_carrier_ok(dev) ||
- (slots > 1 && !xennet_can_sg(dev)) ||
netif_needs_gso(dev, skb, netif_skb_features(skb)))) {
spin_unlock_irqrestore(&queue->tx_lock, flags);
goto drop;
}
+ if (unlikely(slots > 1 && !xennet_can_sg(dev))) {
+ if (skb_linearize(skb)) {
+ spin_unlock_irqrestore(&queue->tx_lock, flags);
+ goto drop;
+ }
+ data = skb->data;
+ offset = offset_in_page(data);
+ len = skb_headlen(skb);
+ }
i = queue->tx.req_prod_pvt;
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