From 47e550e0105be9b716a3860545731735a67c6b3c Mon Sep 17 00:00:00 2001 From: Paolo Abeni Date: Fri, 9 Apr 2021 13:04:39 +0200 Subject: [PATCH] veth: refine napi usage After the previous patch, when enabling GRO, locally generated TCP traffic experiences some measurable overhead, as it traverses the GRO engine without any chance of aggregation. This change refine the NAPI receive path admission test, to avoid unnecessary GRO overhead in most scenarios, when GRO is enabled on a veth peer. Only skbs that are eligible for aggregation enter the GRO layer, the others will go through the traditional receive path. Signed-off-by: Paolo Abeni Signed-off-by: David S. Miller --- drivers/net/veth.c | 23 ++++++++++++++++++++++- 1 file changed, 22 insertions(+), 1 deletion(-) diff --git a/drivers/net/veth.c b/drivers/net/veth.c index c95c67aa52d2..15b2e3923c47 100644 --- a/drivers/net/veth.c +++ b/drivers/net/veth.c @@ -294,6 +294,25 @@ static int veth_forward_skb(struct net_device *dev, struct sk_buff *skb, netif_rx(skb); } +/* return true if the specified skb has chances of GRO aggregation + * Don't strive for accuracy, but try to avoid GRO overhead in the most + * common scenarios. + * When XDP is enabled, all traffic is considered eligible, as the xmit + * device has TSO off. + * When TSO is enabled on the xmit device, we are likely interested only + * in UDP aggregation, explicitly check for that if the skb is suspected + * - the sock_wfree destructor is used by UDP, ICMP and XDP sockets - + * to belong to locally generated UDP traffic. + */ +static bool veth_skb_is_eligible_for_gro(const struct net_device *dev, + const struct net_device *rcv, + const struct sk_buff *skb) +{ + return !(dev->features & NETIF_F_ALL_TSO) || + (skb->destructor == sock_wfree && + rcv->features & (NETIF_F_GRO_FRAGLIST | NETIF_F_GRO_UDP_FWD)); +} + static netdev_tx_t veth_xmit(struct sk_buff *skb, struct net_device *dev) { struct veth_priv *rcv_priv, *priv = netdev_priv(dev); @@ -317,8 +336,10 @@ static netdev_tx_t veth_xmit(struct sk_buff *skb, struct net_device *dev) /* The napi pointer is available when an XDP program is * attached or when GRO is enabled + * Don't bother with napi/GRO if the skb can't be aggregated */ - use_napi = rcu_access_pointer(rq->napi); + use_napi = rcu_access_pointer(rq->napi) && + veth_skb_is_eligible_for_gro(dev, rcv, skb); skb_record_rx_queue(skb, rxq); }