On Wed, Apr 17, 2019 at 10:09:53AM +0200, Eelco Chaudron wrote: > On 16 Apr 2019, at 21:55, Ben Pfaff wrote: > > AF_XDP is a faster way to access the existing kernel devices. If we > > take that point of view, then it would be ideal if AF_XDP were > > automatically used when it was available, instead of adding a new > > network device type. Is there a reason that this point of view is > > wrong? That is, when AF_XDP is available, is there a reason not to use > > it? > > This needs support by all the ingress and egress ports in the system, and > currently, there is no API to check this.
Do you mean for performance or for some other reason? I would suspect that, if AF_XDP was not available, then everything would still work OK via AF_PACKET, just slower. > There are also features like traffic shaping that will not work. Maybe it > will be worth adding the table for AF_XDP in > http://docs.openvswitch.org/en/latest/faq/releases/ AF_XDP is comparable to DPDK/userspace, not to the Linux kernel datapath. The table currently conflates the userspace datapath with the DPDK network device. I believe that the only entry there that depends on the DPDK network device is the one for policing. It could be replaced by a [*] with a note like this: YES - for DPDK network devices. NO - for system or AF_XDP network devices. > > You said that your goal for the next version is to improve performance > > and add optimizations. Do you think that is important before we merge > > the series? We can continue to improve performance after it is merged. > > The previous patch was rather unstable and I could not get it running with > the PVP test without crashing. I think this patchset should get some proper > testing and reviews by others. Especially for all the features being marked > as supported in the above-mentioned table. If it's unstable, we should fix that before adding it in. However, the bar is lower for new features that don't break existing features, especially optional ones and ones that can be easily be removed if they don't work out in the end. DPDK support was considered "experimental" for a long time, it's possible that AF_XDP would be in the same boat for a while. > > If we set performance aside, do you have a reason to want to wait to > > merge this? (I wasn't able to easily apply this series to current > > master, so it'll need at least a rebase before we apply it. And I have > > only skimmed it, not fully reviewed it.) > > Other than the items above, do we really need another datapath? It's less than a new datapath. It's a new network device implementation. > With this, we use two or more cores for processing packets. If we poll > two physical ports it could be 300%, which is a typical use case with > bonding. What about multiple queue support, does it work? Both in > kernel and DPDK mode we use multiple queues to distribute the load, > with this scenario does it double the number of CPUs used? Can we use > the poll() mode as explained here, > https://linuxplumbersconf.org/event/2/contributions/99/, and how will > it work with multiple queues/pmd threads? What about any latency > tests, is it worse or better than kernel/dpdk? Also with the AF_XDP > datapath, there is no to leverage hardware offload, like DPDK and > TC. And then there is the part that it only works on the most recent > kernels. These are good questions. William will have some of the answers. > To me looking at this I would say it’s far from being ready to be merged > into OVS. However, if others decide to go ahead I think it should be > disabled, not compiled in by default. Yes, that seems reasonable to me. _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
