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Received: from AM8PR04MB7779.eurprd04.prod.outlook.com (2603:10a6:20b:24b::14) by AS8PR04MB9110.eurprd04.prod.outlook.com (2603:10a6:20b:449::10) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.7982.22; Fri, 20 Sep 2024 14:25:15 +0000 Received: from AM8PR04MB7779.eurprd04.prod.outlook.com ([fe80::7417:d17f:8d97:44d2]) by AM8PR04MB7779.eurprd04.prod.outlook.com ([fe80::7417:d17f:8d97:44d2%3]) with mapi id 15.20.7982.012; Fri, 20 Sep 2024 14:25:15 +0000 Date: Fri, 20 Sep 2024 17:25:11 +0300 From: Vladimir Oltean To: Wei Fang Cc: Maciej Fijalkowski , "davem@davemloft.net" , "edumazet@google.com" , "kuba@kernel.org" , "pabeni@redhat.com" , Claudiu Manoil , "ast@kernel.org" , "daniel@iogearbox.net" , "hawk@kernel.org" , "john.fastabend@gmail.com" , "linux-kernel@vger.kernel.org" , "netdev@vger.kernel.org" , "bpf@vger.kernel.org" , "stable@vger.kernel.org" , "imx@lists.linux.dev" Subject: Re: [PATCH net 3/3] net: enetc: reset xdp_tx_in_flight when updating bpf program Message-ID: <20240920142511.aph5wpmiczcsxfgr@skbuf> References: <20240919084104.661180-1-wei.fang@nxp.com> <20240919084104.661180-4-wei.fang@nxp.com> Content-Type: text/plain; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?m7Owzn9srrMDWruclAmQ8d9ycsBKfX3BWZplZvgDqpABFPNuIeDH6c9hZ7Zs?= =?us-ascii?Q?aUvhgutJE7DdI6Be52f2BITpPQXwF/U5rYUE0unYkh7t4F2/TLXfEfL9c1uh?= =?us-ascii?Q?7Uu9BtG4zQel0b5b4Ujd01A64jyEQ6GmGGgwurCKFq+wyD8xu1pdMakVb1zN?= =?us-ascii?Q?1W2zXN7vC7kHPn9gRn55iMxXwdfud+iME0DafC54+Y5B3aqXCmCrCpzFHryp?= =?us-ascii?Q?r6KpHoYfUTbO3RAaBurhrOggUw9tD6vfaeo6t4UChvHmGZIatzBIlflVxlcc?= =?us-ascii?Q?jApKHZY2Jfesu/KfCcWbOMRDQqEZfBV0buSINi8vNMDiZUraJO03PimzCJy+?= =?us-ascii?Q?JVmVbYd4KWTxbk45npG3kA9nlr0GOtLVgXwAhpEAIkw2ru7pJjlk6iWSYzWw?= =?us-ascii?Q?uuB9K6hLkXztP+odHbf9n5XUveoOr9v/5d5EH8YhmL3wL5j2+yBMWiJ4BVof?= =?us-ascii?Q?GL1jRW0TGJPN0uM5L+ceMGvkThEx7ZVHmlcwlXBB+7l/wzWP3l99Nb7vpnsp?= =?us-ascii?Q?duJYUw7hQGnqkojC0ba5PVObQ6F5VOA/UM5/aHl+Y6YxoLLVO2OfO0GkbuMT?= =?us-ascii?Q?WFU0PQhcfqGPO1eRclMzRpWr5tcdjN3LmWU31Utg2nbHER8+Yc6Me3iQGGpX?= =?us-ascii?Q?IxB9fkMbVgYkdjRbPOiceni/ZyXh04m+c4WMU6TKHLi8wv2KYqyA906E35bu?= =?us-ascii?Q?eBtBpP2rlU3zVLrDKzYVfntxwisIt7xpdn3W2h0qstpcLWQZLITFfcLaTO4C?= =?us-ascii?Q?eHDFie1a1wrL3ryO5mUU7t6tGVh+AHRXzmV2hrVcItZ/9RDhuqP8XRaWXwVs?= =?us-ascii?Q?nT3hoCfa9vwIX97mh5/Q1jQbawhIkroLUSaa7legEVRqB0ZHlEXapFAds9W0?= =?us-ascii?Q?VYisbYET+77fJrETmWA2hMV93k3F8J9m6HmDJmAO9BruqcWaJkvRJBJ4wtDa?= =?us-ascii?Q?u1stP9pIQqadb97yzHKXDiGiZ11VVUeOF2oRsoqqKutYvLyfshdG6LpmRAy2?= =?us-ascii?Q?PkI2Z+hkKs10jZXcaGT4gXplUAE6zoPPcsQstxy7wFxQikKiJg1bLiaLRTpA?= =?us-ascii?Q?pxScMIRj+wSORPV1qeDy0I91IdO3lTCjcf1PjjoHjvviLP90c6nlq8azbQsK?= =?us-ascii?Q?e/6ZpDlHNxjcVzZ21wcj9IMTmIeQOTp0iaXhkQNDSTMr88zZPgC6NoLWMDiX?= =?us-ascii?Q?4vsfdS8qnH1K72NuibFa9wtF7uvUeDa1/Ayp6sKK4tVPhCPfdoRNx0dGCBHM?= =?us-ascii?Q?lu25/X7MvGXaM8gvIBNGg5HXSO4oBexYeWN3msy1xGSTle9uWtgDCBruvJcB?= =?us-ascii?Q?UqaCigwnIFtia9bMP3U+G92GE5liFBbulqq1ub4t9KVNs97ewDOZRIgXV6J/?= =?us-ascii?Q?dZQeUZWC4wZpJpkmNTfcRIyP7nOYEadclpfcMR7i7Km7gzeX5Y81cEfycBb9?= =?us-ascii?Q?bwu9HnDb9SfhXE9OkVg51uABkcjStB96O+lxIZPfIyU/H0QeL8L1P3bjCUje?= =?us-ascii?Q?Rr1Vek4CAdROEQq7F6TqbYeosyWzSkBNPPacN7rQxUUP0w+2clanHMWHDG/f?= =?us-ascii?Q?oDQvwjonhqLDgOj9Ir243P7z8TItPkIsWSt5tdi0ua/Z14BS3QVNwbJe1oha?= =?us-ascii?Q?7Q=3D=3D?= X-OriginatorOrg: nxp.com X-MS-Exchange-CrossTenant-Network-Message-Id: e777a24a-b7f5-477c-5496-08dcd9800b20 X-MS-Exchange-CrossTenant-AuthSource: AM8PR04MB7779.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 20 Sep 2024 14:25:15.4040 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 686ea1d3-bc2b-4c6f-a92c-d99c5c301635 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: ova1rxVnF68gQkgypHF0edEfnpvzovM2W7slXzu25xfpVl7+pnSat8itt+qJEOh2msoj9LZec7/wz8pXPiNnEw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: AS8PR04MB9110 On Fri, Sep 20, 2024 at 05:05:14PM +0300, Wei Fang wrote: > > zero init is good but shouldn't you be draining these buffers when removing > > XDP resources at least? what happens with DMA mappings that are related to > > these cached buffers? > > > > All the buffers will be freed and DMA will be unmapped when XDP program is > installed. There is still a problem with the patch you proposed here, which is that enetc_reconfigure() has one more call site, from enetc_hwtstamp_set(). If enetc_free_rxtx_rings() is the one that gets rid of the stale buffers, it should also be the one that resets xdp_tx_in_flight, otherwise you will still leave the problem unsolved where XDP_TX can be interrupted by a change in hwtstamping state, and the software "in flight" counter gets out of sync with the ring state. Also, I suspect that the blamed commit is wrong. Also the normal netdev close path should be susceptible to this issue, not just enetc_reconfigure(). Maybe something like ff58fda09096 ("net: enetc: prioritize ability to go down over packet processing"). That's when we started rushing the NAPI poll routing to finish. I don't think it was possible, before that, to close the netdev while there were XDP_TX frames pending to be recycled. > I am thinking that another solution may be better, which is mentioned > in another thread replying to Vladimir, so that xdp_tx_in_flight will naturally drop > to 0, and the TX-related statistics will be more accurate. Please give me some more time to analyze the flow after just your patch 2/3. I have a draft reply, but I would still like to test some things.