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Subject: Re: Driver has suspect GRO implementation, TCP performance may be
 compromised.
To:     Eric Dumazet <eric.dumazet@gmail.com>,
        Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Cc:     intel-wired-lan@lists.osuosl.org,
        Eric Dumazet <edumazet@google.com>, netdev@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
References: <e070e241-fb65-a5b0-3155-7380a9203bcf@molgen.mpg.de>
 <8627ea1e-8e51-c425-97f6-aeb57176e11a@gmail.com>
From:   Paul Menzel <pmenzel@molgen.mpg.de>
Message-ID: <eb730f01-0c6d-0589-36cc-7193d64c1ee8@molgen.mpg.de>
Date:   Wed, 29 May 2019 16:49:28 +0200
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Dear Eric,


Thank you for the quick reply.

On 05/28/19 19:18, Eric Dumazet wrote:
> On 5/28/19 8:42 AM, Paul Menzel wrote:

>> 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:=20
>> 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.
>=20
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index c61edd023b352123e2a77465782e0d32689e96b0..cb0194f66125bcba427e6e7=
e3cacf0c93040ef61 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, cons=
t struct sk_buff *skb,
>                 rcu_read_lock();
>                 dev =3D dev_get_by_index_rcu(sock_net(sk), skb->skb_iif=
);
>                 if (!dev || len >=3D dev->mtu)
> -                       pr_warn("%s: Driver has suspect GRO implementat=
ion, TCP performance may be compromised.\n",
> -                               dev ? dev->name : "Unknown driver");
> +                       pr_warn("%s: Driver has suspect GRO implementat=
ion, TCP performance may be compromised."
> +                               " len %u mtu %u\n",
> +                               dev ? dev->name : "Unknown driver",
> +                               len, dev ? dev->mtu : 0);
>                 rcu_read_unlock();
>         }
>  }

I applied your patch on commit 9fb67d643 (Merge tag 'pinctrl-v5.2-2' of
git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrl):

     [ 5507.291769] TCP: net00: Driver has suspect GRO implementation, TC=
P performance may be compromised. len 1856 mtu 1500


Kind regards,

Paul


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