netdev - Re: [PATCH] i40e: Prevent setting MTU if greater than MFS

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Message-ID: <827d22da-fb32-1012-422d-d283b28ce5ec@intel.com>
Date: Mon, 4 Mar 2024 14:09:46 -0800
From: Tony Nguyen <anthony.l.nguyen@...el.com>
To: Erwan Velu <erwanaliasr1@...il.com>
CC: Erwan Velu <e.velu@...teo.com>, Jesse Brandeburg
	<jesse.brandeburg@...el.com>, "David S. Miller" <davem@...emloft.net>, "Eric
 Dumazet" <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, <intel-wired-lan@...ts.osuosl.org>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] i40e: Prevent setting MTU if greater than MFS

On 2/27/2024 11:27 AM, Erwan Velu wrote:
> Commit 6871a7de705b6f6a4046f0d19da9bcd689c3bc8e from iPXE project is
> setting the MFS to 0x600 = 1536.
> 
> 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 accept 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, but I didn't found a reliable way to do it.
> 
> At least, this 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 the following :
> [  377.548696] i40e 0000:5d:00.0 eno5: Error changing mtu to 9000 which is greater than the current mfs: 1536
> 
> Signed-off-by: Erwan Velu <e.velu@...teo.com>

The Author and Sign-off needs to be fixed; they don't match.

WARNING: From:/Signed-off-by: email address mismatch: 'From: Erwan Velu 
<erwanaliasr1@...il.com>' != 'Signed-off-by: Erwan Velu <e.velu@...teo.com>'

Thanks,
Tony