Re: Driver has suspect GRO implementation, TCP performance may be compromised.

quoted

Occasionally, Linux outputs the message below on the workstation Dell
OptiPlex 5040 MT.

    TCP: net00: Driver has suspect GRO implementation, TCP performance may be compromised.

Linux 4.14.55 and Linux 5.2-rc2 show the message, and the WWW also
gives some hits [1][2].

$ sudo ethtool -i net00
driver: e1000e
version: 3.2.6-k
firmware-version: 0.8-4
expansion-rom-version: 
bus-info: 0000:00:1f.6
supports-statistics: yes
supports-test: yes
supports-eeprom-access: yes
supports-register-dump: yes
supports-priv-flags: no

Can the driver e1000e be improved?

Any idea, what triggers this, as I do not see it every boot? Download
of big files?

Maybe the driver/NIC can receive frames bigger than MTU, although this would be strange.

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index c61edd023b352123e2a77465782e0d32689e96b0..cb0194f66125bcba427e6e7e3cacf0c93040ef61 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c

@@ -150,8 +150,10 @@ static void tcp_gro_dev_warn(struct sock *sk, const struct sk_buff *skb,
                rcu_read_lock();
                dev = dev_get_by_index_rcu(sock_net(sk), skb->skb_iif);
                if (!dev || len >= dev->mtu)
-                       pr_warn("%s: Driver has suspect GRO implementation, TCP performance may be compromised.\n",
-                               dev ? dev->name : "Unknown driver");
+                       pr_warn("%s: Driver has suspect GRO implementation, TCP performance may be compromised."
+                               " len %u mtu %u\n",
+                               dev ? dev->name : "Unknown driver",
+                               len, dev ? dev->mtu : 0);
                rcu_read_unlock();
        }
 }