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Tue, 7 Apr 2026 22:50:35 +0000 Message-ID: <88c37486-70aa-4109-a5b1-ee74cce23bc5@intel.com> Date: Tue, 7 Apr 2026 15:50:32 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net] ice: fix VF queue configuration with low MTU values To: Jose Ignacio Tornos Martinez , CC: , Tony Nguyen , Przemek Kitszel , Andrew Lunn , "David S . Miller" , "Eric Dumazet" , Jakub Kicinski , Paolo Abeni , Aleksandr Loktionov , Michal Swiatkowski , Dave Ertman , Michal Kubiak , References: <20260406145641.1020623-1-jtornosm@redhat.com> From: Jacob Keller Content-Language: en-US In-Reply-To: <20260406145641.1020623-1-jtornosm@redhat.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW4PR04CA0324.namprd04.prod.outlook.com (2603:10b6:303:82::29) To DS0PR11MB7579.namprd11.prod.outlook.com (2603:10b6:8:14d::5) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS0PR11MB7579:EE_|DS4PPF1DFB73954:EE_ X-MS-Office365-Filtering-Correlation-Id: 193f1fac-0ca9-412f-4db1-08de94f81499 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|7416014|1800799024|22082099003|56012099003|18002099003; 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X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: +5x6F+hEIrql128Qrvk3dff8b7Ri+kr2YGWZotb7TW5dVVNUo8fSuiChm7wPWdF77ljJEWtdpzMHNFOo15/Xr/4H5CE9JON8TJY4vRGyVVc= X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS4PPF1DFB73954 X-OriginatorOrg: intel.com On 4/6/2026 7:56 AM, Jose Ignacio Tornos Martinez wrote: > The ice driver's VF queue configuration validation rejects > databuffer_size values below 1024 bytes, which prevents VFs from > using MTU values below 871 bytes. > > The iavf driver calculates databuffer_size based on the MTU using: > databuffer_size = ALIGN(MTU + LIBETH_RX_LL_LEN, 128) > > where LIBETH_RX_LL_LEN = 26 (ETH_HLEN + 2*VLAN_HLEN + ETH_FCS_LEN). > > For MTU values below 871: > MTU 870: 870 + 26 = 896, aligned to 128 = 896 (< 1024, rejected) > MTU 871: 871 + 26 = 897, aligned to 128 = 1024 (>= 1024, accepted) > > The 1024-byte minimum seems unnecessarily restrictive, because the hardware > supports databuffer_size as low as 128 bytes (the alignment boundary), > which should allow MTU values down to the standard minimum of 68 bytes. > > I haven't found the reason why the limit was configured in the commit > 9c7dd7566d18 ("ice: add validation in OP_CONFIG_VSI_QUEUES VF message"), so > with no more information and since it is working, change the minimum > databuffer_size validation from 1024 to 128 bytes to allow standard low > MTU values while still preventing invalid configurations. > I dug through some of our internal history and found that there was no justification on why 1024 was chosen. I agree with your assessment that the value of 128 makes the most sense as it is the actual hardware minimum. I wonder if we used to always use data buffer sizes of 1024 before the conversion to libeth. Either way, I think it makes sense to allow smaller buffers since the modern iAVF will request them. Reviewed-by: Jacob Keller > Fixes: 9c7dd7566d18 ("ice: add validation in OP_CONFIG_VSI_QUEUES VF message") > cc: stable@vger.kernel.org > Signed-off-by: Jose Ignacio Tornos Martinez > --- > drivers/net/ethernet/intel/ice/virt/queues.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/net/ethernet/intel/ice/virt/queues.c b/drivers/net/ethernet/intel/ice/virt/queues.c > index f73d5a3e83d4..31be2f76181c 100644 > --- a/drivers/net/ethernet/intel/ice/virt/queues.c > +++ b/drivers/net/ethernet/intel/ice/virt/queues.c > @@ -840,7 +840,7 @@ int ice_vc_cfg_qs_msg(struct ice_vf *vf, u8 *msg) > > if (qpi->rxq.databuffer_size != 0 && > (qpi->rxq.databuffer_size > ((16 * 1024) - 128) || > - qpi->rxq.databuffer_size < 1024)) > + qpi->rxq.databuffer_size < 128)) > goto error_param; > > ring->rx_buf_len = qpi->rxq.databuffer_size;