Hi Damjan, When it comes to performance, the contiguity prevents DMA transaction coalescing which is required to reach line rate for 64 byte packets at 25Gbps and above.
On a PCI gen 3 x8 lanes slot, you have 50Gbps and roughly 35M DMA transactions per second. This allows reaching 47% of 64 byte line rate of a 50Gbps network adapter. This is also true for PCIx16 for 100Gbps card. With hardware that can handle those DMA coalescing, you need bounce buffers and the cost of packet copy to approach line rate. Allowing non contiguous packet and meta data is a way to keep zero-copy solution. Packet copy is awfully bad to conduct L3F with 1M route on an internet router, way worse than independent reads.... Of course, you could say use PCIx16 for 50Gbps cards but that is also reduces the number of ports that can be installed on a system, should we find systems with enough x16 slots. So even if the rework is significant, does the end goal is worth the cost? -FF On 5 October 2017 at 11:42, Damjan Marion <dmarion.li...@gmail.com> wrote: > Francois, > > Almost every VPP feature assumes that data is adjacent to vlib_buffer_t. > > It will be huge rework to make this happen, and it will slow down performance > as > it will introduce dependent read at many places in the code... > > So to answer your question, we don’t have such plans. > > Thanks, > > Damjan > >> On 4 Oct 2017, at 17:17, Francois Ozog <francois.o...@linaro.org> wrote: >> >> Hi, >> >> Hardware that is capable of 50Gbps and above (at 64 byte line rate) >> place packets next to each other in large memory zones rather than in >> individual memory buffers. >> >> To handle packets without copy would require vlib_buffer_t to allow >> packet data to be NOT consecutive to it. >> >> Are there plans or have there been discussions on this topic before ? >> (I checked the archive and did not found any reference). >> >> -FF >> _______________________________________________ >> vpp-dev mailing list >> vpp-dev@lists.fd.io >> https://lists.fd.io/mailman/listinfo/vpp-dev > -- François-Frédéric Ozog | Director Linaro Networking Group T: +33.67221.6485 francois.o...@linaro.org | Skype: ffozog _______________________________________________ vpp-dev mailing list vpp-dev@lists.fd.io https://lists.fd.io/mailman/listinfo/vpp-dev
