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Fri, 15 Dec 2023 17:32:09 +0000 Date: Fri, 15 Dec 2023 18:32:02 +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="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-ClientProxiedBy: DB7PR05CA0009.eurprd05.prod.outlook.com (2603:10a6:10:36::22) 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_|PH8PR11MB7072:EE_ X-MS-Office365-Filtering-Correlation-Id: edb8674d-5c37-42d2-5040-08dbfd93c3e8 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:PH0PR11MB5782.namprd11.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230031)(376002)(136003)(39860400002)(396003)(346002)(366004)(230922051799003)(64100799003)(451199024)(1800799012)(186009)(6916009)(2906002)(316002)(26005)(66946007)(4326008)(107886003)(8676002)(8936002)(6666004)(53546011)(5660300002)(6506007)(6512007)(9686003)(82960400001)(6486002)(83380400001)(54906003)(66476007)(41300700001)(38100700002)(66556008)(44832011)(478600001)(86362001);DIR:OUT;SFP:1102; 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Will be fixed in v2. > > > > > 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? > > […] > > > 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"). > > Understood. Maybe you could add a summary of the above to the commit message > or just copy and paste. I guess, it’s better than nothing. And thank you for > upstreaming this. > > > Kind regards, > > Paul Right. I have to add some kdocs, so I will also extend that commit message in v2. Thanks, Michal