We started the discussion on the Linux-netdev mailing list about getting our patch to add multicast on UNIX sockets accepted, but, unfortunately, the feedback hasn’t been very good. So, since one of the premises from GENIVI is to get all the work we are doing accepted upstream, we have been thinking in the last few days about what else to use for, as stated in my previous post, fixing the main issue we have found in D-Bus performance, which is the number of context switches needed when getting all traffic on the bus through dbus-daemon. So, here’s a summary of the stuff we have been looking at:
- Use TIPC, a socket family already available in modern kernel versions and which is targeted at clustering environments, although it can be used for communications inside a single node.
- Use ZeroMQ, which is a library that, from a first look, provides the stuff we need for D-Bus, that is multicast on local sockets.
- Provide the multicast on UNIX sockets as a new socket family (AF_MCAST), although this wasn’t well received neither on the linux-netdev discussion. This will contain a trimmed down version of AF_UNIX with only the stuff needed for doing multicast.
- Extend the AF_DBUS work from Alban to include what we have learnt from the multicast AF_UNIX architecture. This would mean having a patch to the kernel that, as with the AF_MCAST solution, would have to be maintained by distributors, as the linux-netdev people didn’t like this solution neither.
- Use Netlink, which has all that we need for D-Bus, that is, multicast and unicast, plus it is an established IPC mechanism in the kernel (from kernel space to user space), and is even used for other services similar to D-Bus. We would create a new Netlink subfamily for D-Bus, that would contain code to do the routing, as Netlink, for security reasons, does not allow direct connection between user space apps.
- Use KBUS, which is a lightweight messaging system, provided as a kernel module.
Right now, we have working code for AF_MCAST, and are looking at Netlink, TIPC and KBUS, so will be blogging more details on what we find out in our experiments. But any feedback would be appreciated since, as stated before, we want to have all this work accepted upstream. So, comments, suggestions?