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X-MS-Exchange-CrossTenant-AuthSource: DS0PR11MB7309.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 Mar 2026 16:22:50.8863 (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: 7JsV2E8IxHM+QxcsKBvXb5HiXUuectbYJflnTgx0co+LaxzHNffhhyInC8UM5xCByTE8dEya8AX3ieZMDjuxr/XeGe7BWNaUs0nlfGma/xM= X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR11MB5125 X-OriginatorOrg: intel.com X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org On Wed, Mar 25, 2026 at 09:19:21AM -0700, Stephen Hemminger wrote: > On Wed, 25 Mar 2026 10:36:56 +0100 > Morten Brørup wrote: > > > If an application clones packets instead of copying them, it is probably for performance reasons. > > If the drivers start copying those clones, it may defeat the performance purpose. > > > > > > Maybe segmentation can be used instead of copying the full packet: > > Make the "copy" packet of two (or more) segments, where the header is copied into a new mbuf (where the VLAN tag is added), and the remaining part of the packet uses an indirect mbuf referring to the "original" packet at the offset after the header. > > > > > > Furthermore... > > If drivers start copying packets in the Tx function, the Tx queue should have its own mbuf pool to allocate these mbufs from. > > Drivers should not steal mbufs from the pools used by the packets being transmitted. > > E.g. if a segmented packet has a small mbuf for the first few bytes, followed by a large mbuf (from another pool) for the remaining bytes. > > Or if the "original" mbuf comes from a mempool allocated on different CPU socket, the "copy" would too. > > > The problem with the Tx function is how backpressure gets handled. > Not sure that it is documented well enough that if a packet is not sent > due to backpressure, the mbuf in the array may still have been replaced. Most drivers should be able to check for space in a Tx ring, or whatever other backpressure mechanism is being used, before modifying a buffer. /Bruce