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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , intel-wired-lan@lists.osuosl.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org References: <20240313090719.33627-2-e.velu@criteo.com> From: Brett Creeley In-Reply-To: <20240313090719.33627-2-e.velu@criteo.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BYAPR05CA0011.namprd05.prod.outlook.com (2603:10b6:a03:c0::24) To PH0PR12MB7982.namprd12.prod.outlook.com (2603:10b6:510:28d::5) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH0PR12MB7982:EE_|DS7PR12MB6359:EE_ X-MS-Office365-Filtering-Correlation-Id: b7918db6-425a-44a6-2997-08dc44413afb X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:PH0PR12MB7982.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230031)(376005)(1800799015)(7416005);DIR:OUT;SFP:1101; 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Use proper caution when opening attachments, clicking links, or responding. > > > Commit 6871a7de705 ("[intelxl] Use admin queue to set port MAC address > and maximum frame size") from iPXE project set the MFS to 0x600 = 1536. > See https://github.com/ipxe/ipxe/commit/6871a7de705 > > At boot time the i40e driver complains about it with > the following message but continues. > > MFS for port 1 has been set below the default: 600 > > If the MTU size is increased, the driver accepts it but large packets will > not be processed by the firmware generating tx_errors. The issue is pretty > silent for users. i.e doing TCP in such context will generates lots of > retransmissions until the proper window size (below 1500) will be used. > > To fix this case, it would have been ideal to increase the MFS, > via i40e_aqc_opc_set_mac_config, incoming patch will take care of it. > > At least, commit prevents setting up an MTU greater than the current MFS. > It will avoid being in the position of having an MTU set to 9000 on the > netdev with a firmware refusing packets larger than 1536. > > A typical trace looks like: > [ 377.548696] i40e 0000:5d:00.0 eno5: Error changing mtu to 9000, Max is 1500. MFS is too small. > > Signed-off-by: Erwan Velu > --- > drivers/net/ethernet/intel/i40e/i40e_main.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c b/drivers/net/ethernet/intel/i40e/i40e_main.c > index f86578857e8a..85ecf2f3de18 100644 > --- a/drivers/net/ethernet/intel/i40e/i40e_main.c > +++ b/drivers/net/ethernet/intel/i40e/i40e_main.c > @@ -2946,7 +2946,7 @@ static int i40e_change_mtu(struct net_device *netdev, int new_mtu) > struct i40e_netdev_priv *np = netdev_priv(netdev); > struct i40e_vsi *vsi = np->vsi; > struct i40e_pf *pf = vsi->back; > - int frame_size; > + int frame_size, mfs, max_mtu; > > frame_size = i40e_max_vsi_frame_size(vsi, vsi->xdp_prog); > if (new_mtu > frame_size - I40E_PACKET_HDR_PAD) { > @@ -2955,6 +2955,14 @@ static int i40e_change_mtu(struct net_device *netdev, int new_mtu) > return -EINVAL; > } > > + mfs = pf->hw.phy.link_info.max_frame_size; > + max_mtu = mfs - I40E_PACKET_HDR_PAD; If this is how the max_mtu is determined, does it make sense to set this before registering the netdev, i.e. netdev->max_mtu in i40e_config_netdev()? Thanks, Brett > + if (new_mtu > max_mtu) { > + netdev_err(netdev, "Error changing mtu to %d, Max is %d. MFS is too small.\n", > + new_mtu, max_mtu); > + return -EINVAL; > + } > + > netdev_dbg(netdev, "changing MTU from %d to %d\n", > netdev->mtu, new_mtu); > netdev->mtu = new_mtu; > -- > 2.44.0 > >