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Wed, 13 Dec 2023 13:23:30 +0000 Date: Wed, 13 Dec 2023 14:23:19 +0100 From: Michal Kubiak To: Paul Menzel CC: Joshua Hay , , , , , , , , Przemek Kitszel Subject: Re: [Intel-wired-lan] [PATCH iwl-net] idpf: enable WB_ON_ITR Message-ID: References: <20231212145546.396273-1-michal.kubiak@intel.com> <78ecdb9f-25e9-4847-87ed-6e8b44a7c71d@molgen.mpg.de> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <78ecdb9f-25e9-4847-87ed-6e8b44a7c71d@molgen.mpg.de> X-ClientProxiedBy: DU2PR04CA0357.eurprd04.prod.outlook.com (2603:10a6:10:2b4::32) To PH0PR11MB5782.namprd11.prod.outlook.com (2603:10b6:510:147::11) 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: PH0PR11MB5782:EE_|PH7PR11MB5793:EE_ X-MS-Office365-Filtering-Correlation-Id: 6e9297f4-2576-4926-1d3c-08dbfbdeb2f4 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?BFWRJ6YFiS1+SkPqivBoxLhoGRQbziVKPRTccCOClfP/6/OpCGoKdHvcCUGl?= =?us-ascii?Q?IBDSXOEWVO6FIYN1zphRucUdW7TCxZ1J/wX6WQh6dYPYwR0QAMTRTTtGeNH0?= =?us-ascii?Q?jXhuzbR7nzqIaTjVwlgdSfbtLe+b0TK7VDDW3Bz65pKd5odWJSTKX6oe6iUI?= =?us-ascii?Q?lOpQj3iYrXW5iDLwqdAbFbEYueRqprnKwCbve8leu04Yohv4+zy/pcoUBc9j?= =?us-ascii?Q?VbyoRxJtwc/tGUcKmzHZoFYU63QkIZCum1oqpMoq496oYzkZgm0T6YvEKQ4s?= =?us-ascii?Q?xtRSfjLYpEE9eRnOCFDrpJ0JQNo8dspuq3fn7NcgrTi90eqBi+5EecEZPYkp?= =?us-ascii?Q?C0Px7fmMvuXtZHTS2jadwTws1bzQpqUi0Hie53QAYIjtPLLtyXzkUAs6PAm1?= =?us-ascii?Q?mkTQtH0/sZmC9HBE9qdUySlrA3LSQFg+q4oJLuz8ZbdZlhlRiHCLSZHhZnB0?= =?us-ascii?Q?B7oivqiI8UKPtVenshXbYyBXMR5kZUaNSEvoZIVa0t23jKWLPzMoSqoSZlQ4?= =?us-ascii?Q?aa7hDsUUAAEGlD3ktSx3j0xOWpMjVmqK6aCfoJ03pNR4rO+fxyCnIxyex97L?= =?us-ascii?Q?aikzA2oKRtaj203X2G7FAyffP5Fm8vAmbX30ra01DPrM4+rgY0Is9BZvH6Ju?= =?us-ascii?Q?oD7i4l3FNRrY8eIOinDCfdEu5+xio3Me8cq/W0vzdAaCLiVSp9l/Oq90NeL/?= =?us-ascii?Q?BEDpGr+f9E5UelWBEiy5Vp0239DjPIs439B3ce4rQZQeEFTM3VoDhpcZUziq?= =?us-ascii?Q?4wxsq7EwcwKevOnGYCHslh7ba095+eqv5BrToIAMlWMezyFWsfjuytsmYXUC?= =?us-ascii?Q?SZTm51QPUtWW6tt8RRCmAJBp7YCazAdMMqWPBxOdqsvYm2KoqxX7Q2oFA3uF?= =?us-ascii?Q?gldotDg4ZW49ojTOMyVqKm0+WWCqja+u0G5LL0hgk1lkrMdZ22gkMKTAA1MC?= =?us-ascii?Q?OAX9eLwre/Rxo9f+fZut1hwJ9u84yzZ5hQYtl9wIkEbTEgOGDKvctBy9PV8v?= =?us-ascii?Q?utneAfK2KZaCX2cRgeU+uJldeBs184N85k+r5vyM0JXIZN+VAREelMD3yVfE?= =?us-ascii?Q?O6Gl8NF13z3WQXGGrxhuuiEd91AlbhQsN6ucX7+RPyAFEqUJAJhwbypXVRTl?= =?us-ascii?Q?BVO6TpRzde1R2sZGR0VLKXffL4EOjk+ANB7IuveFd6223BEZqbMt1HyyerJZ?= =?us-ascii?Q?zFI+JIei/bMs9tpwb7j2ptCtM3ieIfNkevjbWXGN/kUFtxqJ2wekO2oL2GCU?= =?us-ascii?Q?48G4yUcy1AJ3XGh55Z2SltAs6ciMToQUrGjGG9ZPZVr2gx0OSTqoxVQ4B4lI?= =?us-ascii?Q?xZpvjC3ieazP2+AQFGlc01orM/DpvOM0/DmERVYtxMlTzcc+WeTd7JEgp/wu?= =?us-ascii?Q?laRC7OiY3DedvHrcvkYJfpf1iSo73HfuBh1rj3dYJuYsjAYZuA7AUU1MLknL?= =?us-ascii?Q?ozQeJCoxqrD4FGPhLszUfirGOkjdmvv0TLf/PQPhTdBYQZRQDI/kQWdZoNL2?= =?us-ascii?Q?g9BwCYkt4Xp1hqyjy++bXGftt4zpWT9+ynnQGyLH3tEpY0SjdTVr428c/0xx?= =?us-ascii?Q?SuPahTExTaN55D7VESPziThaetfJ3HNF5/pflCV7eiL+N7vniZd66tlU5ng1?= =?us-ascii?Q?Eg=3D=3D?= X-MS-Exchange-CrossTenant-Network-Message-Id: 6e9297f4-2576-4926-1d3c-08dbfbdeb2f4 X-MS-Exchange-CrossTenant-AuthSource: PH0PR11MB5782.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 13 Dec 2023 13:23:30.7876 (UTC) 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: GyGDH34C7JBZ9MT28oRnwCjIkP4JwWwLocxETMFoTc6BRKNh+Qm2X6AeMOn1UE+hFwAc4X2Uipip8AzGWlXkyQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR11MB5793 X-OriginatorOrg: intel.com On Tue, Dec 12, 2023 at 05:50:55PM +0100, Paul Menzel wrote: > Dear Michal, dear Joshua, > > > Thank you for your patch. > > On 12/12/23 15:55, Michal Kubiak wrote: > > From: Joshua Hay > > > > Tell hardware to writeback completed descriptors even when interrupts > > Should you resend, the verb is spelled with a space: write back. Sure, I will fix it. > > > are disabled. Otherwise, descriptors might not be written back until > > the hardware can flush a full cacheline of descriptors. This can cause > > unnecessary delays when traffic is light (or even trigger Tx queue > > timeout). > > How can the problem be reproduced and the patch be verified? > > > Kind regards, > > Paul > > Hi Paul, To be honest, I have noticed the problem during the implementation of AF_XDP feature for IDPF driver. In my scenario, I had 2 Tx queues: - regular LAN Tx queue - and XDP Tx queue added to the same q_vector attached to the same NAPI, so those 2 Tx queues were handled in the same NAPI poll loop. Then, when I started a huge Tx zero-copy trafic using AF_XDP (on the XDP queue), and, at the same time, tried to xmit a few packets using the second (non-XDP) queue (e.g. with scapy), I was getting the Tx timeout on that regular LAN Tx queue. That is why I decided to upstream this fix. With disabled writebacks, there is no chance to get the completion descriptor for the queue where the traffic is much lighter. I have never tried to reproduce the scenario described by Joshua in his original patch ("unnecessary delays when traffic is light"). Thanks, Michal