On Wed, 25 Mar 2026 10:36:56 +0100 Morten Brørup <[email protected]> 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. > > <brainstorming> > 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. > </brainstorming> > > 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.
