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Subject: Re: Driver has suspect GRO implementation, TCP performance may be
 compromised.
To:     Eric Dumazet <edumazet@google.com>
Cc:     Eric Dumazet <eric.dumazet@gmail.com>,
        Jeff Kirsher <jeffrey.t.kirsher@intel.com>,
        intel-wired-lan@lists.osuosl.org, netdev <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>
 <eb730f01-0c6d-0589-36cc-7193d64c1ee8@molgen.mpg.de>
 <CANn89i+VvwMaHy2Br-0CcC3gPQ+PmG3Urpn4KpqL0P7XBykmcw@mail.gmail.com>
From:   Paul Menzel <pmenzel@molgen.mpg.de>
Message-ID: <f370d2c0-aeca-88cf-66e6-7767881d05c8@molgen.mpg.de>
Date:   Mon, 22 Jul 2019 18:04:06 +0200
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Dear Eric,


Sorry for the late reply.


On 5/29/19 6:00 PM, Eric Dumazet wrote:
> On Wed, May 29, 2019 at 7:49 AM Paul Menzel <pmenzel@molgen.mpg.de> wro=
te:

>> 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 Del=
l
>>>> OptiPlex 5040 MT.
>>>>
>>>>     TCP: net00: Driver has suspect GRO implementation, TCP performan=
ce 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? Downloa=
d
>>>> of big files?
>>>>
>>> Maybe the driver/NIC can receive frames bigger than MTU, although thi=
s would be strange.
>>>
>>> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
>>> index c61edd023b352123e2a77465782e0d32689e96b0..cb0194f66125bcba427e6=
e7e3cacf0c93040ef61 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, co=
nst struct sk_buff *skb,
>>>                 rcu_read_lock();
>>>                 dev =3D dev_get_by_index_rcu(sock_net(sk), skb->skb_i=
if);
>>>                 if (!dev || len >=3D dev->mtu)
>>> -                       pr_warn("%s: Driver has suspect GRO implement=
ation, TCP performance may be compromised.\n",
>>> -                               dev ? dev->name : "Unknown driver");
>>> +                       pr_warn("%s: Driver has suspect GRO implement=
ation, 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' o=
f
>> git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrl):
>>
>>      [ 5507.291769] TCP: net00: Driver has suspect GRO implementation,=
 TCP performance may be compromised. len 1856 mtu 1500
>=20
>=20
> The 'GRO' in the warning can be probably ignored, since this NIC does
> not implement its own GRO.
>=20
> You can confirm this with this debug patch:
>=20
> diff --git a/drivers/net/ethernet/intel/e1000e/netdev.c
> b/drivers/net/ethernet/intel/e1000e/netdev.c
> index 0e09bede42a2bd2c912366a68863a52a22def8ee..014a43ce77e09664bda0568=
dd118064b006acd67
> 100644
> --- a/drivers/net/ethernet/intel/e1000e/netdev.c
> +++ b/drivers/net/ethernet/intel/e1000e/netdev.c
> @@ -561,6 +561,9 @@ static void e1000_receive_skb(struct e1000_adapter =
*adapter,
>         if (staterr & E1000_RXD_STAT_VP)
>                 __vlan_hwaccel_put_tag(skb, htons(ETH_P_8021Q), tag);
>=20
> +       if (skb->len > netdev->mtu)
> +               pr_err_ratelimited("received packet bigger (%u) than
> MTU (%u)\n",
> +                                  skb->len, netdev->mtu);
>         napi_gro_receive(&adapter->napi, skb);
>  }

With this patch applied, I unfortunately could not trigger the condition
anymore. No idea why. Or is that expected?

(As a side note, plain Linux 5.2.2 still shows the warning.)


Kind regards,

Paul


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