Having thought more about it, I think that a completely different architectural approach is required:
Many of the DPDK Ethernet PMDs implement a variety of RX and TX packet burst functions, each optimized for different CPU vector instruction sets. The availability of a DMA engine should be treated the same way. So I suggest that PMDs copying packet contents, e.g. memif, pcap, vmxnet3, should implement DMA optimized RX and TX packet burst functions. Similarly for the DPDK vhost library. In such an architecture, it would be the application's job to allocate DMA channels and assign them to the specific PMDs that should use them. But the actual use of the DMA channels would move down below the application and into the DPDK PMDs and libraries. Med venlig hilsen / Kind regards, -Morten Brørup From: Pai G, Sunil [mailto:sunil.pa...@intel.com] Sent: Monday, 28 March 2022 20.19 To: Stokes, Ian; Hu, Jiayu; Ferriter, Cian; Van Haaren, Harry; Ilya Maximets; Maxime Coquelin (maxime.coque...@redhat.com); ovs-...@openvswitch.org; dev@dpdk.org Cc: Mcnamara, John; O'Driscoll, Tim; Finn, Emma Subject: RE: OVS DPDK DMA-Dev library/Design Discussion Hi All, Please see below PDF which will be presented in the call. https://github.com/Sunil-Pai-G/OVS-DPDK-presentation-share/blob/main/OVS%20vhost%20async%20datapath%20design%202022%20session%202.pdf <https://github.com/Sunil-Pai-G/OVS-DPDK-presentation-share/blob/main/OVS%20vhost%20async%20datapath%20design%202022%20session%202.pdf> Thanks and Regards, Sunil -----Original Appointment----- From: Stokes, Ian <ian.sto...@intel.com> Sent: Thursday, March 24, 2022 9:07 PM To: Pai G, Sunil; Hu, Jiayu; Ferriter, Cian; Van Haaren, Harry; Ilya Maximets; Maxime Coquelin (maxime.coque...@redhat.com); ovs-...@openvswitch.org; dev@dpdk.org Cc: Mcnamara, John; O'Driscoll, Tim; Finn, Emma Subject: OVS DPDK DMA-Dev library/Design Discussion When: Tuesday, March 29, 2022 2:00 PM-3:00 PM (UTC+00:00) Dublin, Edinburgh, Lisbon, London. Where: Google Meet Hi All, This meeting is a follow up to the call earlier this week. This week Sunil presented 3 different approaches to integrating DMA-Dev with OVS along with the performance impacts. https://github.com/Sunil-Pai-G/OVS-DPDK-presentation-share/blob/main/OVS%20vhost%20async%20datapath%20design%202022.pdf <https://github.com/Sunil-Pai-G/OVS-DPDK-presentation-share/blob/main/OVS%20vhost%20async%20datapath%20design%202022.pdf> The approaches were as follows: · Defer work. · Tx completions from Rx context. · Tx completions from Rx context + lockless ring. The pros and cons of each approach were discussed but there was no clear solution reached. As such a follow up call was suggested to continue discussion and to reach a clear decision on the approach to take. Please see agenda as it stands below: Agenda · Opens · Continue discussion of 3x approaches from last week (Defer work, "V3", V4, links to patches in Sunil's slides above) · Design Feedback (please review solutions of above & slide-deck from last week before call to be informed) · Dynamic Allocation of DMA engine per queue · Code Availability (DPDK GitHub, OVS GitHub branches) Please feel free to respond with any other items to be added to the agenda. Google Meet: https://meet.google.com/hme-pygf-bfb <https://meet.google.com/hme-pygf-bfb> Regards Ian
